Chapter ndash V
155
Synthesis Characterization and Applications of CeO2 Nanoparticles
51 Introduction
Ceria (CeO2) is an oxide with important applications in areas of catalysis
electrochemistry photochemistry and materials science [1-5] Also it is highly
efficient ultraviolet (UV) absorber to protect light-sensitive materials as a coating
material for protection of corrosion of metals as an oxidation catalyst and as a
counter electrode for electrochemical devices [6-9] The physical properties of
CeO2 are represented in Table 51 Cerium oxide has outstanding physical and
chemical properties therefore it is used as LPG sensor as well as electrolyte
materials for solid fuel cells [10-13] Recently Zhang et al has reported the CeO2
nanocrystal microsphers as a novel adsorbent for the removal of Cr (VI) from
waste water [4] In its most stable phase bulk CeO2 adopts a fluorite-type crystal
structure in which each metal cation is surrounded by eight oxygen atoms The
band gap of pure ceria is 5 eV but crystal defects or impurities can transform the
material in a good n-type semiconductor [14] Experimental and theoretical studies
indicate that bulk CeO2 is not a fully ionic oxide [15] Experiments of
photoelectron spectroscopies and optical reflectivity measurements show a strong
hybridization of the metal and oxygen orbitals and the valence band although
dominated by O 2p character still contains a significant amount of metal character
[16] Thus the charge on the metal cations is probably much smaller than the
formal value of +4 frequently assigned and CeO2 is best described as an
ionocovalent compound or covalent insulator One of the most interesting
properties of ceria is its ability to undergo a facile conversion between +4 and +3
formal oxidation states Because of this ceria is a key component in the so-called
three-way catalysts (TWC) commonly used to reduce the emissions of CO NOx
and hydrocarbons from automobile exhaust or is used as a base material of
electrolytes and electrodes in solid oxide fuel cells [17-20] Ceria-supported noble
metal catalysts are capable of storing oxygen under oxidizing conditions and
Chapter ndash V
156
releasing oxygen under reducing conditions through a transformation between
Ce4+
and Ce3+
oxidation states [21-23]
Table 51 Properties of CeO2
Molecular formula CeO2
Molar mass 172115 gmol
Appearance white or pale yellow solid
slightly hygroscopic
Density 765 gcm3 solid
7215 gcm3 fluorite phase
Melting point 2400degC
Boiling point 3500degC
Solubility in water Insoluble
In the area of catalysis nanoparticles of ceria have been studied since the
early 1970s but they were poorly characterized In recent years substantial
progress has been made thanks the use of better synthetic methods and
sophisticated techniques for characterizing structural and electronic properties
Only for the largest nanoparticles was the fluorite structure clearly observed
Small nanoparticles exhibited a nearly amorphous structure [24-29] In general
the energy required to reduce the CenO2n systems increased with particle size but
large fluctuations were also observed The reduction of the ceria nanoparticles was
structure sensitive being easier in systems that had a low degree of crystallinity
Several of these theoretical predictions have been verified by subsequent
experimental studies as we will see bellow
Chapter ndash V
157
It is not easy to find synthetic methods that allow the preparation of ceria
nanoparticles that are small and have a narrow distribution of sizes This makes
difficult a direct comparison between experiment and theory [30] But
experimentally it is known that very small particles of ceria may deviate from the
fluorite structure of the bulk oxide For particles that are a little bit larger
measurements of XAS Raman and XRD would suggest the existence of local
distortions on the cubic fluorite structure as a consequence of defects in the oxide
lattice [31-34] Depending on the method of preparation and particularly of the
Ce oxidation state of the precursor salt the content of O vacancies and
concomitant presence of Ce3+
in a ceria nanoparticle can change this has been
shown by using Raman and XRD Since Ce3+
is significantly bigger than Ce4+
(atomic sizes 114 and 097 Aring respectively) the presence of O vacancies increases
the size of the unit cell and can distort it In addition to O vacancies other
structural imperfections as well as surface effects can be present in a ceria
nanoparticle introducing strain in the lattice The O vacancies and defects present
in ceria nanoparticles can lead to special electronic properties introducing
electronic states within the band gap of the oxide [35-39] Ceria particles with
diameters of less than 10 nm have a substantially higher electronic conductivity
than bulk ceria [40-43]
Bulk ceria is able to absorb and store hydrogen Ceria nanoparticles have
the same property The absorption of hydrogen causes an expansion in the lattice
constant of the oxide detected by using XRD [44] Theoretical calculations
indicate that the H atoms do not remain at a high symmetry position in the center
of the cavities of the ceria lattice but instead move toward the O sites forming
hydroxyl species [45-49] These species can be seen as the precursors for the
removal of oxygen during a reduction process Results of temperature
programmed reduction and time-resolved XRD indicate that ceria nanoparticles
are reduced at temperatures that are lower than those seen for the reduction of bulk
ceria This is consistent with the prediction of theoretical studies During the
Chapter ndash V
158
reduction process before the appearance of Ce2O3 there is a substantial expansion
in the unit cell of the CeO2 nanoparticles as a consequence of the embedding of
hydrogen and the formation of O vacancies [50]
The fine powder of CeO2 has been prepared by many methods including
forced hydrolysis sol-gel hydrothermal coprecipitation surfactant templating
method and spray pyrolysis [51-57] However microwave synthesis is very
beneficial to find a fast simple and energy efficient approach to produce fine
CeO2 nanoparticles [20 58-63] It is relatively new method to produce inorganic
compounds for materials processing to enhance the material properties as well as
economic advantages through energy saving and acceleration of product
development [64-65]
In the present work we have studied the structural optical and electrical
properties of CeO2 nanoparticles This material was characterized by using
UV-Visible FTIR XRD SEM EDAX TEM TGA-DTA and electrical
conductivity The CeO2 nanoparticles have been investigated for gas sensing
properties for LPG gas catalytic activity for the oxidative regeneration of ketones
and novel adsorbents for wastewater treatment
52 Materials and Methods
All the chemicals used for the preparation were of analytical grade It
includes Cerium nitrate (Ce (NO3)3 6H2O) propylene glycol and ammonia All the
solutions were prepared in millipore water obtained from ultra pure water system
Monodispersed nanocrystalline CeO2 powder was prepared by controlled addition
of aqueous ammonia to a mixture of 01M aqueous solution of cerium nitrate and
propylene glycol until the solution reached pH = 10 The ratio of concentration of
propylene glycol to cerium nitrate solution was kept 11 The special arrangement
was made to add drop wise aqueous ammonia into the solution with constant
stirring After complete precipitation the precipitated hydroxide was washed with
distilled water Then pure hydroxide in a glass beaker was placed in a microwave
Chapter ndash V
159
oven (in put power 600W) about 30 minutes with on-off cycle The Phase purity
and the degree of crystallinity of the resulting CeO2 sample were monitored by
XRD analysis The schematic flow chart of preparation of nanocrystalline CeO2 is
represented in Fig51
Aqueous ammonia
darr
Ce(NO3)3 6H2O + Propylene glycol
darr Centrifugation and washing
Microwave treatment
darr
CeO2 nanocrystalline particles
Fig51 Schematic Flow Chart for the preparation of nanocrystalline CeO2
The powder Xndashray diffraction patterns were recorded on Philips PW-1710
X-ray diffractometer by using Cr Kα radiation The lattice parameters were
calculated using high angle reflection of XRD by using the following formula
--- 51
Crystallite size was calculated by using the Scherrerrsquos formula having
wavelength of X-ray (Cr Kα line 228 Aring)
The UV-Visible Spectra were recorded on UV-Visible-NIR
Spectrophotometer (UV-3600 Shimadzu Japan)
Chapter ndash V
160
FTIR spectrum was recorded with a Perkin Elmer-USA in the range of
wavenumber from 4000-400 cm-1
The SEM micrographs of the samples were obtained using the scanning
electron microscope (Model JEOL-JSM 6360) Elemental analysis was carried
out by using the energy dispersive X-ray spectroscopy equipped with Scanning
electron microscopy
TEM study of the powder sample was carried out by using model Philips
CM 12 transmission electron microscope with Energy Dispersive Spectroscopy
(EDS) detector for microanalysis (IIT-Madras)
The thermal behavior of the nanocrystalline CeO2 powder is studied upto 10
to1000degC in nitrogen using SDT Q600 V209 Build 20 Instrument
The oxidation of oxime was carried out at 353 K in presence of cerium
oxide as catalyst ethyl acetate as a solvent and H2O2 as the oxidant [19] The
liquid phase reaction was carried out in 25 ml round bottom flask equipped with a
reflux condenser In catalytic oxidation reaction oxime (10 mmol) H2O2
(20 mmol) along with catalyst (1 by wt of the substrate) and the content were
heated in pre-heated oil bath at 353 K
NOH
R
O
R
H2O
2
CeO2
Oxime Ketone
Where R = CH3 C6H5
One hundred milligrams of CeO2 nanocrystal microspheres was suspended
in 100 mL of rhodamine B aqueous solution with a concentration of 20 mg L-1
in a
flask under stirring The flask was covered with carbon paper to prevent the
Chapter ndash V
161
photodegradation of Rh B At different intervals 5mL of the suspensions was
collected filtered through a 045μm membrane and finally analyzed by a
UV-visible spectrophotometer immediately [22]
53 Results and Discussion
531 UV-Visible Spectroscopic Analysis
The absorption spectra of CeO2 nanoparticles dispersed in ethanol solution
is shown in Fig52 The absorption edge of the CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC occurs at
around 400 nm and its band gap energy is estimated to be 31 eV A sharp band is
an indicative of narrow distribution of particles within the matrix The accurate
band gap of material was 31 eV as obtained by plotting (αhυ)2
against hυ shown
in Fig53
Fig 52 UV-Visible absorption spectrum of CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC
Chapter ndash V
162
In semiconductors the band gap will be increased as particle size is
decreased As particles shrink in size there is a dramatic change in valence band
and conduction bands as the continuous density of states in bulk is replaced with a
set of discrete energy levels This leads to interesting optical properties In the
visible region colour can changes with size Since with increase in size energy
decreases the nanoparticles which have size less than the bulk compound shows
blue shift in the UV-Visible spectra of nanoparticles This blue shift may be
considered as one of the confirmatory test for the existence of nanoparticles
Fig53 Variation of (αhυ) 2
vs Photon Energy (eV) of CeO2 nanoparticle synthesized
a) by microwave (without annealed) annealed at b)200degC and c) 300degC
532 FTIR Analysis
The FT-IR spectrum of the obtained ceria nanoparticles is shown in
Fig 54 Three strong absorption peaks were observed at 3381 1558 and
1372 cm-1
The former was attributed to the stretching band of hydroxyl group and
the others were attributed to the antisymmetric and symmetric stretching band of
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
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[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
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[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
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[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
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[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
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[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
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[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
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[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
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[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
156
releasing oxygen under reducing conditions through a transformation between
Ce4+
and Ce3+
oxidation states [21-23]
Table 51 Properties of CeO2
Molecular formula CeO2
Molar mass 172115 gmol
Appearance white or pale yellow solid
slightly hygroscopic
Density 765 gcm3 solid
7215 gcm3 fluorite phase
Melting point 2400degC
Boiling point 3500degC
Solubility in water Insoluble
In the area of catalysis nanoparticles of ceria have been studied since the
early 1970s but they were poorly characterized In recent years substantial
progress has been made thanks the use of better synthetic methods and
sophisticated techniques for characterizing structural and electronic properties
Only for the largest nanoparticles was the fluorite structure clearly observed
Small nanoparticles exhibited a nearly amorphous structure [24-29] In general
the energy required to reduce the CenO2n systems increased with particle size but
large fluctuations were also observed The reduction of the ceria nanoparticles was
structure sensitive being easier in systems that had a low degree of crystallinity
Several of these theoretical predictions have been verified by subsequent
experimental studies as we will see bellow
Chapter ndash V
157
It is not easy to find synthetic methods that allow the preparation of ceria
nanoparticles that are small and have a narrow distribution of sizes This makes
difficult a direct comparison between experiment and theory [30] But
experimentally it is known that very small particles of ceria may deviate from the
fluorite structure of the bulk oxide For particles that are a little bit larger
measurements of XAS Raman and XRD would suggest the existence of local
distortions on the cubic fluorite structure as a consequence of defects in the oxide
lattice [31-34] Depending on the method of preparation and particularly of the
Ce oxidation state of the precursor salt the content of O vacancies and
concomitant presence of Ce3+
in a ceria nanoparticle can change this has been
shown by using Raman and XRD Since Ce3+
is significantly bigger than Ce4+
(atomic sizes 114 and 097 Aring respectively) the presence of O vacancies increases
the size of the unit cell and can distort it In addition to O vacancies other
structural imperfections as well as surface effects can be present in a ceria
nanoparticle introducing strain in the lattice The O vacancies and defects present
in ceria nanoparticles can lead to special electronic properties introducing
electronic states within the band gap of the oxide [35-39] Ceria particles with
diameters of less than 10 nm have a substantially higher electronic conductivity
than bulk ceria [40-43]
Bulk ceria is able to absorb and store hydrogen Ceria nanoparticles have
the same property The absorption of hydrogen causes an expansion in the lattice
constant of the oxide detected by using XRD [44] Theoretical calculations
indicate that the H atoms do not remain at a high symmetry position in the center
of the cavities of the ceria lattice but instead move toward the O sites forming
hydroxyl species [45-49] These species can be seen as the precursors for the
removal of oxygen during a reduction process Results of temperature
programmed reduction and time-resolved XRD indicate that ceria nanoparticles
are reduced at temperatures that are lower than those seen for the reduction of bulk
ceria This is consistent with the prediction of theoretical studies During the
Chapter ndash V
158
reduction process before the appearance of Ce2O3 there is a substantial expansion
in the unit cell of the CeO2 nanoparticles as a consequence of the embedding of
hydrogen and the formation of O vacancies [50]
The fine powder of CeO2 has been prepared by many methods including
forced hydrolysis sol-gel hydrothermal coprecipitation surfactant templating
method and spray pyrolysis [51-57] However microwave synthesis is very
beneficial to find a fast simple and energy efficient approach to produce fine
CeO2 nanoparticles [20 58-63] It is relatively new method to produce inorganic
compounds for materials processing to enhance the material properties as well as
economic advantages through energy saving and acceleration of product
development [64-65]
In the present work we have studied the structural optical and electrical
properties of CeO2 nanoparticles This material was characterized by using
UV-Visible FTIR XRD SEM EDAX TEM TGA-DTA and electrical
conductivity The CeO2 nanoparticles have been investigated for gas sensing
properties for LPG gas catalytic activity for the oxidative regeneration of ketones
and novel adsorbents for wastewater treatment
52 Materials and Methods
All the chemicals used for the preparation were of analytical grade It
includes Cerium nitrate (Ce (NO3)3 6H2O) propylene glycol and ammonia All the
solutions were prepared in millipore water obtained from ultra pure water system
Monodispersed nanocrystalline CeO2 powder was prepared by controlled addition
of aqueous ammonia to a mixture of 01M aqueous solution of cerium nitrate and
propylene glycol until the solution reached pH = 10 The ratio of concentration of
propylene glycol to cerium nitrate solution was kept 11 The special arrangement
was made to add drop wise aqueous ammonia into the solution with constant
stirring After complete precipitation the precipitated hydroxide was washed with
distilled water Then pure hydroxide in a glass beaker was placed in a microwave
Chapter ndash V
159
oven (in put power 600W) about 30 minutes with on-off cycle The Phase purity
and the degree of crystallinity of the resulting CeO2 sample were monitored by
XRD analysis The schematic flow chart of preparation of nanocrystalline CeO2 is
represented in Fig51
Aqueous ammonia
darr
Ce(NO3)3 6H2O + Propylene glycol
darr Centrifugation and washing
Microwave treatment
darr
CeO2 nanocrystalline particles
Fig51 Schematic Flow Chart for the preparation of nanocrystalline CeO2
The powder Xndashray diffraction patterns were recorded on Philips PW-1710
X-ray diffractometer by using Cr Kα radiation The lattice parameters were
calculated using high angle reflection of XRD by using the following formula
--- 51
Crystallite size was calculated by using the Scherrerrsquos formula having
wavelength of X-ray (Cr Kα line 228 Aring)
The UV-Visible Spectra were recorded on UV-Visible-NIR
Spectrophotometer (UV-3600 Shimadzu Japan)
Chapter ndash V
160
FTIR spectrum was recorded with a Perkin Elmer-USA in the range of
wavenumber from 4000-400 cm-1
The SEM micrographs of the samples were obtained using the scanning
electron microscope (Model JEOL-JSM 6360) Elemental analysis was carried
out by using the energy dispersive X-ray spectroscopy equipped with Scanning
electron microscopy
TEM study of the powder sample was carried out by using model Philips
CM 12 transmission electron microscope with Energy Dispersive Spectroscopy
(EDS) detector for microanalysis (IIT-Madras)
The thermal behavior of the nanocrystalline CeO2 powder is studied upto 10
to1000degC in nitrogen using SDT Q600 V209 Build 20 Instrument
The oxidation of oxime was carried out at 353 K in presence of cerium
oxide as catalyst ethyl acetate as a solvent and H2O2 as the oxidant [19] The
liquid phase reaction was carried out in 25 ml round bottom flask equipped with a
reflux condenser In catalytic oxidation reaction oxime (10 mmol) H2O2
(20 mmol) along with catalyst (1 by wt of the substrate) and the content were
heated in pre-heated oil bath at 353 K
NOH
R
O
R
H2O
2
CeO2
Oxime Ketone
Where R = CH3 C6H5
One hundred milligrams of CeO2 nanocrystal microspheres was suspended
in 100 mL of rhodamine B aqueous solution with a concentration of 20 mg L-1
in a
flask under stirring The flask was covered with carbon paper to prevent the
Chapter ndash V
161
photodegradation of Rh B At different intervals 5mL of the suspensions was
collected filtered through a 045μm membrane and finally analyzed by a
UV-visible spectrophotometer immediately [22]
53 Results and Discussion
531 UV-Visible Spectroscopic Analysis
The absorption spectra of CeO2 nanoparticles dispersed in ethanol solution
is shown in Fig52 The absorption edge of the CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC occurs at
around 400 nm and its band gap energy is estimated to be 31 eV A sharp band is
an indicative of narrow distribution of particles within the matrix The accurate
band gap of material was 31 eV as obtained by plotting (αhυ)2
against hυ shown
in Fig53
Fig 52 UV-Visible absorption spectrum of CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC
Chapter ndash V
162
In semiconductors the band gap will be increased as particle size is
decreased As particles shrink in size there is a dramatic change in valence band
and conduction bands as the continuous density of states in bulk is replaced with a
set of discrete energy levels This leads to interesting optical properties In the
visible region colour can changes with size Since with increase in size energy
decreases the nanoparticles which have size less than the bulk compound shows
blue shift in the UV-Visible spectra of nanoparticles This blue shift may be
considered as one of the confirmatory test for the existence of nanoparticles
Fig53 Variation of (αhυ) 2
vs Photon Energy (eV) of CeO2 nanoparticle synthesized
a) by microwave (without annealed) annealed at b)200degC and c) 300degC
532 FTIR Analysis
The FT-IR spectrum of the obtained ceria nanoparticles is shown in
Fig 54 Three strong absorption peaks were observed at 3381 1558 and
1372 cm-1
The former was attributed to the stretching band of hydroxyl group and
the others were attributed to the antisymmetric and symmetric stretching band of
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
157
It is not easy to find synthetic methods that allow the preparation of ceria
nanoparticles that are small and have a narrow distribution of sizes This makes
difficult a direct comparison between experiment and theory [30] But
experimentally it is known that very small particles of ceria may deviate from the
fluorite structure of the bulk oxide For particles that are a little bit larger
measurements of XAS Raman and XRD would suggest the existence of local
distortions on the cubic fluorite structure as a consequence of defects in the oxide
lattice [31-34] Depending on the method of preparation and particularly of the
Ce oxidation state of the precursor salt the content of O vacancies and
concomitant presence of Ce3+
in a ceria nanoparticle can change this has been
shown by using Raman and XRD Since Ce3+
is significantly bigger than Ce4+
(atomic sizes 114 and 097 Aring respectively) the presence of O vacancies increases
the size of the unit cell and can distort it In addition to O vacancies other
structural imperfections as well as surface effects can be present in a ceria
nanoparticle introducing strain in the lattice The O vacancies and defects present
in ceria nanoparticles can lead to special electronic properties introducing
electronic states within the band gap of the oxide [35-39] Ceria particles with
diameters of less than 10 nm have a substantially higher electronic conductivity
than bulk ceria [40-43]
Bulk ceria is able to absorb and store hydrogen Ceria nanoparticles have
the same property The absorption of hydrogen causes an expansion in the lattice
constant of the oxide detected by using XRD [44] Theoretical calculations
indicate that the H atoms do not remain at a high symmetry position in the center
of the cavities of the ceria lattice but instead move toward the O sites forming
hydroxyl species [45-49] These species can be seen as the precursors for the
removal of oxygen during a reduction process Results of temperature
programmed reduction and time-resolved XRD indicate that ceria nanoparticles
are reduced at temperatures that are lower than those seen for the reduction of bulk
ceria This is consistent with the prediction of theoretical studies During the
Chapter ndash V
158
reduction process before the appearance of Ce2O3 there is a substantial expansion
in the unit cell of the CeO2 nanoparticles as a consequence of the embedding of
hydrogen and the formation of O vacancies [50]
The fine powder of CeO2 has been prepared by many methods including
forced hydrolysis sol-gel hydrothermal coprecipitation surfactant templating
method and spray pyrolysis [51-57] However microwave synthesis is very
beneficial to find a fast simple and energy efficient approach to produce fine
CeO2 nanoparticles [20 58-63] It is relatively new method to produce inorganic
compounds for materials processing to enhance the material properties as well as
economic advantages through energy saving and acceleration of product
development [64-65]
In the present work we have studied the structural optical and electrical
properties of CeO2 nanoparticles This material was characterized by using
UV-Visible FTIR XRD SEM EDAX TEM TGA-DTA and electrical
conductivity The CeO2 nanoparticles have been investigated for gas sensing
properties for LPG gas catalytic activity for the oxidative regeneration of ketones
and novel adsorbents for wastewater treatment
52 Materials and Methods
All the chemicals used for the preparation were of analytical grade It
includes Cerium nitrate (Ce (NO3)3 6H2O) propylene glycol and ammonia All the
solutions were prepared in millipore water obtained from ultra pure water system
Monodispersed nanocrystalline CeO2 powder was prepared by controlled addition
of aqueous ammonia to a mixture of 01M aqueous solution of cerium nitrate and
propylene glycol until the solution reached pH = 10 The ratio of concentration of
propylene glycol to cerium nitrate solution was kept 11 The special arrangement
was made to add drop wise aqueous ammonia into the solution with constant
stirring After complete precipitation the precipitated hydroxide was washed with
distilled water Then pure hydroxide in a glass beaker was placed in a microwave
Chapter ndash V
159
oven (in put power 600W) about 30 minutes with on-off cycle The Phase purity
and the degree of crystallinity of the resulting CeO2 sample were monitored by
XRD analysis The schematic flow chart of preparation of nanocrystalline CeO2 is
represented in Fig51
Aqueous ammonia
darr
Ce(NO3)3 6H2O + Propylene glycol
darr Centrifugation and washing
Microwave treatment
darr
CeO2 nanocrystalline particles
Fig51 Schematic Flow Chart for the preparation of nanocrystalline CeO2
The powder Xndashray diffraction patterns were recorded on Philips PW-1710
X-ray diffractometer by using Cr Kα radiation The lattice parameters were
calculated using high angle reflection of XRD by using the following formula
--- 51
Crystallite size was calculated by using the Scherrerrsquos formula having
wavelength of X-ray (Cr Kα line 228 Aring)
The UV-Visible Spectra were recorded on UV-Visible-NIR
Spectrophotometer (UV-3600 Shimadzu Japan)
Chapter ndash V
160
FTIR spectrum was recorded with a Perkin Elmer-USA in the range of
wavenumber from 4000-400 cm-1
The SEM micrographs of the samples were obtained using the scanning
electron microscope (Model JEOL-JSM 6360) Elemental analysis was carried
out by using the energy dispersive X-ray spectroscopy equipped with Scanning
electron microscopy
TEM study of the powder sample was carried out by using model Philips
CM 12 transmission electron microscope with Energy Dispersive Spectroscopy
(EDS) detector for microanalysis (IIT-Madras)
The thermal behavior of the nanocrystalline CeO2 powder is studied upto 10
to1000degC in nitrogen using SDT Q600 V209 Build 20 Instrument
The oxidation of oxime was carried out at 353 K in presence of cerium
oxide as catalyst ethyl acetate as a solvent and H2O2 as the oxidant [19] The
liquid phase reaction was carried out in 25 ml round bottom flask equipped with a
reflux condenser In catalytic oxidation reaction oxime (10 mmol) H2O2
(20 mmol) along with catalyst (1 by wt of the substrate) and the content were
heated in pre-heated oil bath at 353 K
NOH
R
O
R
H2O
2
CeO2
Oxime Ketone
Where R = CH3 C6H5
One hundred milligrams of CeO2 nanocrystal microspheres was suspended
in 100 mL of rhodamine B aqueous solution with a concentration of 20 mg L-1
in a
flask under stirring The flask was covered with carbon paper to prevent the
Chapter ndash V
161
photodegradation of Rh B At different intervals 5mL of the suspensions was
collected filtered through a 045μm membrane and finally analyzed by a
UV-visible spectrophotometer immediately [22]
53 Results and Discussion
531 UV-Visible Spectroscopic Analysis
The absorption spectra of CeO2 nanoparticles dispersed in ethanol solution
is shown in Fig52 The absorption edge of the CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC occurs at
around 400 nm and its band gap energy is estimated to be 31 eV A sharp band is
an indicative of narrow distribution of particles within the matrix The accurate
band gap of material was 31 eV as obtained by plotting (αhυ)2
against hυ shown
in Fig53
Fig 52 UV-Visible absorption spectrum of CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC
Chapter ndash V
162
In semiconductors the band gap will be increased as particle size is
decreased As particles shrink in size there is a dramatic change in valence band
and conduction bands as the continuous density of states in bulk is replaced with a
set of discrete energy levels This leads to interesting optical properties In the
visible region colour can changes with size Since with increase in size energy
decreases the nanoparticles which have size less than the bulk compound shows
blue shift in the UV-Visible spectra of nanoparticles This blue shift may be
considered as one of the confirmatory test for the existence of nanoparticles
Fig53 Variation of (αhυ) 2
vs Photon Energy (eV) of CeO2 nanoparticle synthesized
a) by microwave (without annealed) annealed at b)200degC and c) 300degC
532 FTIR Analysis
The FT-IR spectrum of the obtained ceria nanoparticles is shown in
Fig 54 Three strong absorption peaks were observed at 3381 1558 and
1372 cm-1
The former was attributed to the stretching band of hydroxyl group and
the others were attributed to the antisymmetric and symmetric stretching band of
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
158
reduction process before the appearance of Ce2O3 there is a substantial expansion
in the unit cell of the CeO2 nanoparticles as a consequence of the embedding of
hydrogen and the formation of O vacancies [50]
The fine powder of CeO2 has been prepared by many methods including
forced hydrolysis sol-gel hydrothermal coprecipitation surfactant templating
method and spray pyrolysis [51-57] However microwave synthesis is very
beneficial to find a fast simple and energy efficient approach to produce fine
CeO2 nanoparticles [20 58-63] It is relatively new method to produce inorganic
compounds for materials processing to enhance the material properties as well as
economic advantages through energy saving and acceleration of product
development [64-65]
In the present work we have studied the structural optical and electrical
properties of CeO2 nanoparticles This material was characterized by using
UV-Visible FTIR XRD SEM EDAX TEM TGA-DTA and electrical
conductivity The CeO2 nanoparticles have been investigated for gas sensing
properties for LPG gas catalytic activity for the oxidative regeneration of ketones
and novel adsorbents for wastewater treatment
52 Materials and Methods
All the chemicals used for the preparation were of analytical grade It
includes Cerium nitrate (Ce (NO3)3 6H2O) propylene glycol and ammonia All the
solutions were prepared in millipore water obtained from ultra pure water system
Monodispersed nanocrystalline CeO2 powder was prepared by controlled addition
of aqueous ammonia to a mixture of 01M aqueous solution of cerium nitrate and
propylene glycol until the solution reached pH = 10 The ratio of concentration of
propylene glycol to cerium nitrate solution was kept 11 The special arrangement
was made to add drop wise aqueous ammonia into the solution with constant
stirring After complete precipitation the precipitated hydroxide was washed with
distilled water Then pure hydroxide in a glass beaker was placed in a microwave
Chapter ndash V
159
oven (in put power 600W) about 30 minutes with on-off cycle The Phase purity
and the degree of crystallinity of the resulting CeO2 sample were monitored by
XRD analysis The schematic flow chart of preparation of nanocrystalline CeO2 is
represented in Fig51
Aqueous ammonia
darr
Ce(NO3)3 6H2O + Propylene glycol
darr Centrifugation and washing
Microwave treatment
darr
CeO2 nanocrystalline particles
Fig51 Schematic Flow Chart for the preparation of nanocrystalline CeO2
The powder Xndashray diffraction patterns were recorded on Philips PW-1710
X-ray diffractometer by using Cr Kα radiation The lattice parameters were
calculated using high angle reflection of XRD by using the following formula
--- 51
Crystallite size was calculated by using the Scherrerrsquos formula having
wavelength of X-ray (Cr Kα line 228 Aring)
The UV-Visible Spectra were recorded on UV-Visible-NIR
Spectrophotometer (UV-3600 Shimadzu Japan)
Chapter ndash V
160
FTIR spectrum was recorded with a Perkin Elmer-USA in the range of
wavenumber from 4000-400 cm-1
The SEM micrographs of the samples were obtained using the scanning
electron microscope (Model JEOL-JSM 6360) Elemental analysis was carried
out by using the energy dispersive X-ray spectroscopy equipped with Scanning
electron microscopy
TEM study of the powder sample was carried out by using model Philips
CM 12 transmission electron microscope with Energy Dispersive Spectroscopy
(EDS) detector for microanalysis (IIT-Madras)
The thermal behavior of the nanocrystalline CeO2 powder is studied upto 10
to1000degC in nitrogen using SDT Q600 V209 Build 20 Instrument
The oxidation of oxime was carried out at 353 K in presence of cerium
oxide as catalyst ethyl acetate as a solvent and H2O2 as the oxidant [19] The
liquid phase reaction was carried out in 25 ml round bottom flask equipped with a
reflux condenser In catalytic oxidation reaction oxime (10 mmol) H2O2
(20 mmol) along with catalyst (1 by wt of the substrate) and the content were
heated in pre-heated oil bath at 353 K
NOH
R
O
R
H2O
2
CeO2
Oxime Ketone
Where R = CH3 C6H5
One hundred milligrams of CeO2 nanocrystal microspheres was suspended
in 100 mL of rhodamine B aqueous solution with a concentration of 20 mg L-1
in a
flask under stirring The flask was covered with carbon paper to prevent the
Chapter ndash V
161
photodegradation of Rh B At different intervals 5mL of the suspensions was
collected filtered through a 045μm membrane and finally analyzed by a
UV-visible spectrophotometer immediately [22]
53 Results and Discussion
531 UV-Visible Spectroscopic Analysis
The absorption spectra of CeO2 nanoparticles dispersed in ethanol solution
is shown in Fig52 The absorption edge of the CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC occurs at
around 400 nm and its band gap energy is estimated to be 31 eV A sharp band is
an indicative of narrow distribution of particles within the matrix The accurate
band gap of material was 31 eV as obtained by plotting (αhυ)2
against hυ shown
in Fig53
Fig 52 UV-Visible absorption spectrum of CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC
Chapter ndash V
162
In semiconductors the band gap will be increased as particle size is
decreased As particles shrink in size there is a dramatic change in valence band
and conduction bands as the continuous density of states in bulk is replaced with a
set of discrete energy levels This leads to interesting optical properties In the
visible region colour can changes with size Since with increase in size energy
decreases the nanoparticles which have size less than the bulk compound shows
blue shift in the UV-Visible spectra of nanoparticles This blue shift may be
considered as one of the confirmatory test for the existence of nanoparticles
Fig53 Variation of (αhυ) 2
vs Photon Energy (eV) of CeO2 nanoparticle synthesized
a) by microwave (without annealed) annealed at b)200degC and c) 300degC
532 FTIR Analysis
The FT-IR spectrum of the obtained ceria nanoparticles is shown in
Fig 54 Three strong absorption peaks were observed at 3381 1558 and
1372 cm-1
The former was attributed to the stretching band of hydroxyl group and
the others were attributed to the antisymmetric and symmetric stretching band of
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
159
oven (in put power 600W) about 30 minutes with on-off cycle The Phase purity
and the degree of crystallinity of the resulting CeO2 sample were monitored by
XRD analysis The schematic flow chart of preparation of nanocrystalline CeO2 is
represented in Fig51
Aqueous ammonia
darr
Ce(NO3)3 6H2O + Propylene glycol
darr Centrifugation and washing
Microwave treatment
darr
CeO2 nanocrystalline particles
Fig51 Schematic Flow Chart for the preparation of nanocrystalline CeO2
The powder Xndashray diffraction patterns were recorded on Philips PW-1710
X-ray diffractometer by using Cr Kα radiation The lattice parameters were
calculated using high angle reflection of XRD by using the following formula
--- 51
Crystallite size was calculated by using the Scherrerrsquos formula having
wavelength of X-ray (Cr Kα line 228 Aring)
The UV-Visible Spectra were recorded on UV-Visible-NIR
Spectrophotometer (UV-3600 Shimadzu Japan)
Chapter ndash V
160
FTIR spectrum was recorded with a Perkin Elmer-USA in the range of
wavenumber from 4000-400 cm-1
The SEM micrographs of the samples were obtained using the scanning
electron microscope (Model JEOL-JSM 6360) Elemental analysis was carried
out by using the energy dispersive X-ray spectroscopy equipped with Scanning
electron microscopy
TEM study of the powder sample was carried out by using model Philips
CM 12 transmission electron microscope with Energy Dispersive Spectroscopy
(EDS) detector for microanalysis (IIT-Madras)
The thermal behavior of the nanocrystalline CeO2 powder is studied upto 10
to1000degC in nitrogen using SDT Q600 V209 Build 20 Instrument
The oxidation of oxime was carried out at 353 K in presence of cerium
oxide as catalyst ethyl acetate as a solvent and H2O2 as the oxidant [19] The
liquid phase reaction was carried out in 25 ml round bottom flask equipped with a
reflux condenser In catalytic oxidation reaction oxime (10 mmol) H2O2
(20 mmol) along with catalyst (1 by wt of the substrate) and the content were
heated in pre-heated oil bath at 353 K
NOH
R
O
R
H2O
2
CeO2
Oxime Ketone
Where R = CH3 C6H5
One hundred milligrams of CeO2 nanocrystal microspheres was suspended
in 100 mL of rhodamine B aqueous solution with a concentration of 20 mg L-1
in a
flask under stirring The flask was covered with carbon paper to prevent the
Chapter ndash V
161
photodegradation of Rh B At different intervals 5mL of the suspensions was
collected filtered through a 045μm membrane and finally analyzed by a
UV-visible spectrophotometer immediately [22]
53 Results and Discussion
531 UV-Visible Spectroscopic Analysis
The absorption spectra of CeO2 nanoparticles dispersed in ethanol solution
is shown in Fig52 The absorption edge of the CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC occurs at
around 400 nm and its band gap energy is estimated to be 31 eV A sharp band is
an indicative of narrow distribution of particles within the matrix The accurate
band gap of material was 31 eV as obtained by plotting (αhυ)2
against hυ shown
in Fig53
Fig 52 UV-Visible absorption spectrum of CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC
Chapter ndash V
162
In semiconductors the band gap will be increased as particle size is
decreased As particles shrink in size there is a dramatic change in valence band
and conduction bands as the continuous density of states in bulk is replaced with a
set of discrete energy levels This leads to interesting optical properties In the
visible region colour can changes with size Since with increase in size energy
decreases the nanoparticles which have size less than the bulk compound shows
blue shift in the UV-Visible spectra of nanoparticles This blue shift may be
considered as one of the confirmatory test for the existence of nanoparticles
Fig53 Variation of (αhυ) 2
vs Photon Energy (eV) of CeO2 nanoparticle synthesized
a) by microwave (without annealed) annealed at b)200degC and c) 300degC
532 FTIR Analysis
The FT-IR spectrum of the obtained ceria nanoparticles is shown in
Fig 54 Three strong absorption peaks were observed at 3381 1558 and
1372 cm-1
The former was attributed to the stretching band of hydroxyl group and
the others were attributed to the antisymmetric and symmetric stretching band of
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
160
FTIR spectrum was recorded with a Perkin Elmer-USA in the range of
wavenumber from 4000-400 cm-1
The SEM micrographs of the samples were obtained using the scanning
electron microscope (Model JEOL-JSM 6360) Elemental analysis was carried
out by using the energy dispersive X-ray spectroscopy equipped with Scanning
electron microscopy
TEM study of the powder sample was carried out by using model Philips
CM 12 transmission electron microscope with Energy Dispersive Spectroscopy
(EDS) detector for microanalysis (IIT-Madras)
The thermal behavior of the nanocrystalline CeO2 powder is studied upto 10
to1000degC in nitrogen using SDT Q600 V209 Build 20 Instrument
The oxidation of oxime was carried out at 353 K in presence of cerium
oxide as catalyst ethyl acetate as a solvent and H2O2 as the oxidant [19] The
liquid phase reaction was carried out in 25 ml round bottom flask equipped with a
reflux condenser In catalytic oxidation reaction oxime (10 mmol) H2O2
(20 mmol) along with catalyst (1 by wt of the substrate) and the content were
heated in pre-heated oil bath at 353 K
NOH
R
O
R
H2O
2
CeO2
Oxime Ketone
Where R = CH3 C6H5
One hundred milligrams of CeO2 nanocrystal microspheres was suspended
in 100 mL of rhodamine B aqueous solution with a concentration of 20 mg L-1
in a
flask under stirring The flask was covered with carbon paper to prevent the
Chapter ndash V
161
photodegradation of Rh B At different intervals 5mL of the suspensions was
collected filtered through a 045μm membrane and finally analyzed by a
UV-visible spectrophotometer immediately [22]
53 Results and Discussion
531 UV-Visible Spectroscopic Analysis
The absorption spectra of CeO2 nanoparticles dispersed in ethanol solution
is shown in Fig52 The absorption edge of the CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC occurs at
around 400 nm and its band gap energy is estimated to be 31 eV A sharp band is
an indicative of narrow distribution of particles within the matrix The accurate
band gap of material was 31 eV as obtained by plotting (αhυ)2
against hυ shown
in Fig53
Fig 52 UV-Visible absorption spectrum of CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC
Chapter ndash V
162
In semiconductors the band gap will be increased as particle size is
decreased As particles shrink in size there is a dramatic change in valence band
and conduction bands as the continuous density of states in bulk is replaced with a
set of discrete energy levels This leads to interesting optical properties In the
visible region colour can changes with size Since with increase in size energy
decreases the nanoparticles which have size less than the bulk compound shows
blue shift in the UV-Visible spectra of nanoparticles This blue shift may be
considered as one of the confirmatory test for the existence of nanoparticles
Fig53 Variation of (αhυ) 2
vs Photon Energy (eV) of CeO2 nanoparticle synthesized
a) by microwave (without annealed) annealed at b)200degC and c) 300degC
532 FTIR Analysis
The FT-IR spectrum of the obtained ceria nanoparticles is shown in
Fig 54 Three strong absorption peaks were observed at 3381 1558 and
1372 cm-1
The former was attributed to the stretching band of hydroxyl group and
the others were attributed to the antisymmetric and symmetric stretching band of
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
161
photodegradation of Rh B At different intervals 5mL of the suspensions was
collected filtered through a 045μm membrane and finally analyzed by a
UV-visible spectrophotometer immediately [22]
53 Results and Discussion
531 UV-Visible Spectroscopic Analysis
The absorption spectra of CeO2 nanoparticles dispersed in ethanol solution
is shown in Fig52 The absorption edge of the CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC occurs at
around 400 nm and its band gap energy is estimated to be 31 eV A sharp band is
an indicative of narrow distribution of particles within the matrix The accurate
band gap of material was 31 eV as obtained by plotting (αhυ)2
against hυ shown
in Fig53
Fig 52 UV-Visible absorption spectrum of CeO2 nanoparticles synthesized
a) by microwave (without annealed) annealed at b) 200degC and c) 300degC
Chapter ndash V
162
In semiconductors the band gap will be increased as particle size is
decreased As particles shrink in size there is a dramatic change in valence band
and conduction bands as the continuous density of states in bulk is replaced with a
set of discrete energy levels This leads to interesting optical properties In the
visible region colour can changes with size Since with increase in size energy
decreases the nanoparticles which have size less than the bulk compound shows
blue shift in the UV-Visible spectra of nanoparticles This blue shift may be
considered as one of the confirmatory test for the existence of nanoparticles
Fig53 Variation of (αhυ) 2
vs Photon Energy (eV) of CeO2 nanoparticle synthesized
a) by microwave (without annealed) annealed at b)200degC and c) 300degC
532 FTIR Analysis
The FT-IR spectrum of the obtained ceria nanoparticles is shown in
Fig 54 Three strong absorption peaks were observed at 3381 1558 and
1372 cm-1
The former was attributed to the stretching band of hydroxyl group and
the others were attributed to the antisymmetric and symmetric stretching band of
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
162
In semiconductors the band gap will be increased as particle size is
decreased As particles shrink in size there is a dramatic change in valence band
and conduction bands as the continuous density of states in bulk is replaced with a
set of discrete energy levels This leads to interesting optical properties In the
visible region colour can changes with size Since with increase in size energy
decreases the nanoparticles which have size less than the bulk compound shows
blue shift in the UV-Visible spectra of nanoparticles This blue shift may be
considered as one of the confirmatory test for the existence of nanoparticles
Fig53 Variation of (αhυ) 2
vs Photon Energy (eV) of CeO2 nanoparticle synthesized
a) by microwave (without annealed) annealed at b)200degC and c) 300degC
532 FTIR Analysis
The FT-IR spectrum of the obtained ceria nanoparticles is shown in
Fig 54 Three strong absorption peaks were observed at 3381 1558 and
1372 cm-1
The former was attributed to the stretching band of hydroxyl group and
the others were attributed to the antisymmetric and symmetric stretching band of
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
163
the glycol group respectively In the present synthesis propylene glycol works as
a protective agent against particle growth and since the stretching band of the
carbonyl around 1700 cm-1
was not observed in the FT-IR spectrum it could be
that the surface of the ceria nanoparticles was covered with glycol species In
addition it has also been reported that non-stoichiometric cerium oxide
synthesized by an inert gas condensation process was brownish yellow
Fig54 FTIR spectrum of CeO2 nanoparticles
533 The XRD Analysis
Fig55 shows the X-ray diffractograms of the as prepared powder of CeO2
nanoparticles a) by microwave (without annealed) annealed at b)200degC and
c) 300degC The CeO2 nanoparticles are crystalline in nature with d values 313
270 191 and 163 Aring The synthesized samples by microwave confirmed the
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
164
formation of face centered cubic structure (FCC) of CeO2 nanoparticles The
determined characteristics 2θ values and [hkl] planes are 4287deg [111] 5017deg
[200] 7386deg [220] and 89deg [311] respectively (JCPDS card No 81-0792) and
lattice parameter is 542 Aring The average particle size of CeO2 nanoparticles was
found to about 10 nm The particle size of CeO2 nanoparticles obtained by
microwave is less than that of annealed at 200degC and 300degC However the lattice
parameter is found to increase with reduction temperature indicating an expansion
in the FCC lattice
Fig 55 XRD patterns of the CeO2 nanoparticles synthesized a) by microwave
(without annealed) annealed at b) 200degC and c) 300degC
To know the correct structure in cubic the indexing pattern of cubic crystal
was studied in detail A cubic crystal gives diffraction lines whose sin2θ values
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
165
satisfy the equation obtained by combining the Braggrsquos law with the plane-spacing
equation for the cubic system as
sin2θ (h
2+k
2+l
2) = sin
2θ s = λ
2 4 a
2 --- 52
Since the sum (s) =
(h
2+k
2+l
2) is always integral and λ
2 4a
2 is a constant for any
one pattern of a cubic substance is one of finding a set of integers (s) which will
yield a constant quotient when divided one by one into the observed sin2θ values
Once the proper integers (s) are found the indices (hkl) of each line can be written
down by inspection The proper set of integers (s) is not hard to find because there
are only a few possible sets [30] Each of the four common cubic lattice types has
a characteristic sequence of diffraction lines described by their sequential values
Simple cubic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 -------
Body-centered cubic 2 4 6 8 10 12 14 16 -------
Face-centered cubic 3 4 8 11 12 16 --------
In our case the crystal system was found to be face centered cubic (FCC) because
the integers(s) 3 4 8 11 which matches the FCC diffractions lines
Fig 56 Fluorite structure of CeO2
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
166
The unit cell of ceria is shown in Fig56 In the face centered cubic (FCC)
structure of ceria Ce4+
ions form a cubic close packing arrangement and all the
tetrahedral sites are occupied by the oxide ions whereas the octahedral sites remain
vacant The unit cell of ceria can be considered as a simple cube in which the face
center positions and corners are occupied by Ce4+
ions The tetrahedral sites can be
visualized by dividing the cube into eight smaller cubes The body center positions
of all the small cubes are occupied by oxide ions and the alternate corners are
occupied by Ce4+
ions [31]
Fig57 βcos θ λ vs sin θ λ for CeO2 nanocrystals
The particle size of CeO2 nanoparticles was calculated by using Scherrerrsquos
formula The lattice strain and crystalline size was calculated from the following
equation [18]
β cos θ λ = (1 ε) + (τ sin θ λ) --- 53
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
167
where β is the measured FWHM (Full Width at Half Maximum) in radian θ is the
Bragg angle of the peak λ is wavelength of X-ray (Cr Kα line 228 Aring) ε is the
effective particle size and τ is the effective strain The average particle size can be
estimated from the extrapolation of the Williamson-Hall plot shown in Fig 57
and the particle size was obtained 9 nm based on the intercept inverse
ie 1 ε = 0011 X 108
which yields ε = 909 X 10-9
m or 9 nm
534 Energy Dispersive Analysis of X-Rays (EDAX)
The cerium oxide nanoparticles were characterized by energy dispersive
X- ray analysis (EDAX) which is attachment of SEM The sample for EDAX was
prepared by depositing a very thin layer of cerium oxide nanoparticles on glass
slide The dispersive X ndash ray analysis was conducted by focusing an electron beam
on several different sectioned regions of copper nanoparticles
Fig58 EDAX spectrum of CeO2 nanoparticles
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
168
The EDAX spectrum of cerium oxide nano particles synthesized by
microwave assisted sol-gel method is shown in Fig58 the composition of sample
shows the presense of cerium and oxygen elements The spectrum peak reveals the
presence of Ce and O at 4837 and 0525 keV respectively The atomic of Ce
and O is 3597 and 6403 respectively which confirms the presence of Ce and O in
the powder The present composition of Ce and O reveals that the formation of
non-stoichometric CeO2 which is superior for adsorption of toxic ions from
wastewater
535 Scanning Electron Microscopic (SEM) Analysis
The model JEOL JSM-6360 was used for the determination of morphology
of nanoparticle The cerium oxide nanoparticles were dispersed in isopropyl
alcohol and sonicated for frac12 hour One or two drop of sonicated solution was kept
on 1x1 cm glass plate dried naturally and coated the platinum The SEM images
are formed by scanning narrow beam of electrons across the surface of specimen
Fig59 (a) SEM micrograph of CeO2 nanoparticles by microwave
(without annealed)
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
169
Collecting and processing emitting electron and displaying them on cathode ray
tubecomputer monitor Using a visual raster which is synchronized with the
beams scanned The dried thin films samples of cerium oxide nanoparticles were
scanned by SEM The SEM images of cerium oxide synthesized by microwave
(without annealed) and annealed at 300degC are shown in Figs59 (a) and (b) From
SEM images revealed that there were various sizes of particles in the as-prepared
sample The large particles are composed of small crystallites and show particle
aggregates of irregular shapes The particles are spherical in shapes which are
good agreement with XRD results of particles size These observations were
consistent with similar observations reported in the literature [42ndash44]
Fig59 (b) SEM micrograph of CeO2 nanoparticles annealed at 300degC
536 Transmission Electron Microscopic (TEM) Analysis
In case of cerium oxide the transmission electron micrograph was obtained
by employing Philips microscopy IIT Madras TEM is analogous to the optical
microscope It provides very high resolution which can reach approximately
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
170
01 nm in the case of lattice images Consequently very high magnification can be
obtained TEM is used to examine very thin section through materials of the
surface A transmission electron microscope Philips 120 kV is equipped with CCD
camera This instrument has the resolution of 036 nm with 42 to 120 kV operating
voltage and magnifies object upto 6 lakhs times in high resolution mode Samples
for TEM examinations were prepared by placing a drop of sample suspension on a
copper grade coated with carbon film and were allowed to dry in air A typical
TEM image of CeO2 powders synthesized by cerium nitrate salts by microwave
assisted sol-gel method (without calcination) is presented in Fig 510 The mean
diameter of the particles as measured is about 10 nm These results are in good
agreement with that of estimated by X-ray line broadening Also the synthesized
Fig510 TEM image of the CeO2 nanoparticles
nanopowder is well crystallized without defects non-agglomerated with narrow
size distributions The selected area electron diffraction (SAED) pattern shown in
the Fig511 it also supports the d values obtained from XRD with rings which
can be assigned [111] [200] [220] and [311] diffractions of CeO2 structure
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
171
Fig511 SAED image of the CeO2 nanoparticles
537 Thermo-Gravimetric and Differential Thermal Analysis
Fig512 shows the TG-DTA curves for the dried ceria precursor prepared
by the Ce(IV) methods The dried samples may consist of three portions of
materials (A) crystalline ceria CeO2 (B) crystalline ceria with structural water
CeO22H2O and (C) amorphous cerium hydroxide Ce(OH)4 The endothermic
peaks in 64degC could be due to crystallization of the amorphous portion in the
sample Ce(OH)4 to crystalline CeO2 The larger endothermic peak for the sample
indicates that the former contains more amorphous phase than the latter The total
weight loss up to 800 degC for the sample is about 1685 (or 194 for n which is
the number of water molecules per mole of cerium in the dried sample) This is
consistent with the change of [Ce (OH)4 + CeO22H2O] to [CeO2] The two
endothermic peaks at about 313 and 436degC in figure can be attributed to the loss of
the structural water molecules The less obvious endothermic peaks for the
structural water loss for this sample also agree with the weight loss data These
results suggest that the Ce(IV) derived sample contains primarily Ce(OH)4 and
CeO22H2O
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
172
Fig 512 Weight loss of CeO2 nanoparticles as a function of temperature
538 Electrical Conductivity of Semiconductors CeO2
Semiconductors find wide appilication particularly in electronics Their
application is based on certain properties that will be an electrical conductivity of
semiconductors When the temperature is not very low the semiconductor will
conduct electricity due to the movement of the electrons in the conduction band
and that of holes in the valence band The conductivity of nano CeO2 thick film is
represented in Fig513 From the figure the almost linear relationship was found
in the measured temperature range of 200-500oC If it assumed that conduction in
crystalline ceria is essentially an n-type electronic process then using a simple
model we can express the conductivity-temperature relation by the equation
σ = σo e-Ea kT
where σo is a constant Ea is thermal activation energy T is the
Kelvin temperature and k is Boltzmanns constant Thus an Arrhenius plot of
conductivity and temperature should be linear over certain temperature range
Although the results in Fig513 are curved a linear section can be drawn above
280oC which gives activation energy of 236 eV
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
173
Fig513 Electrical conductivity of CeO2 nanoparticles as a function of temperature
539 Gas Sensing Performance
5391 LPG Gas Sensing
Fig514 shows the variation of response of CeO2 fired at various
temperature The gas response increases with temperature from 50 to 150degC and
then decreases with a further increase in temperature In present work every time
prior to exposing the CeO2 film to LPG it was allowed to stabilize at an operating
temperature for 10 min and the stabilized resistance was taken as Ra After
exposing the film to the LPG gas the changed resistance was taken as Rg LPG
reacts with surface oxygen ions of the film Oxidation of film decreases the
number of free carriers Therefore resistance of the film increases with gas The
result of reaction of LPG with polycrystalline CeO2 is adsorbed CO2 and H2O on
the surface of the oxide The Ce harrLPG interactions on CeO2 are strong and Ce
sites probably get oxidized
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
174
Fig 514 Variation of gas responses with operating temperature for LPG gas
5393 Effect of Gas Concentration (active region)
The variation of sensor response of CeO2 thick film sample with LPG gas
concentration at operating temperature 150degC is represented in Fig 515
Fig 515 Variation in sensor response with LPG gas concentration
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
175
It is clear from the figure that the gas response goes on increasing with gas
concentration upto 600 ppm The rate of increase in response was relatively large
upto 1000 ppm and saturated beyond 600 ppm The monolayer of the gas
molecules formed on the surface covers the whole surface of the film The gas
molecules from that layer would reach the surface active sites of the film The
excess gas molecules remain idle and would not reach the surface active sites of
the sensor Thus the active region of the sensor would be up to 600 ppm
5394 Response and Recovery Time
The response of CeO2 thick film sensor was found to be quick (~ 28 s) to
600 ppm of while the recovery was fast (~ 10 s) (Fig 516) The fast response
may be attributed to faster oxidation of the gas The negligible quantity of the
surface reaction product and its high volatility explains its fast response and quick
recovery to its initial chemical status
Fig 516 Response and recovery time
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
176
5395 Oxygen Adsorption-Desorption Mechanism
O2 (air) + 2e- 2O
-(film surface) --- 56
At higher temperature the atmospheric oxygen O2 adsorbs on the surface of the
thick film It captures the electrons (Fig517) from conduction band It would
result in decreasing conductivity of the film When LPG reacts with the adsorbed
oxygen on the surface of the film it gets oxidized to CO2 and H2O by following
series of intermediate stages This liberates free electrons in the conduction band
The final reaction takes place as
C4H10(gas) + 13Ominus
(filmsurface) rarr 4CO2(gas) + 5H2O(gas) + 13eminus
(condband) --- 57
Fig 517 Sensing mechanism on the surface of the film
This shows n-type conduction mechanism Thus generated electrons
contribute to a sudden increase in conductance of the thick film The mass of
Ce and O in sample was not as per the stoichiometric proportion and sample was
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
177
observed to be the oxygen deficient This deficiency gets reduced due to
adsorption of atmosphericmolecular oxygen This helps in decreasing electronic
conductivity of the film Upon exposure LPG molecules got oxidized with the
adsorbed oxygen ions by following the series of intermediate stages producing
CO2 and H2O This results in evolving oxygen as electrically neutral atoms
trapping behind the negative charges (electrons) Upon exposure the energy
released in decomposition of LPG molecules would be sufficient for trapped
electrons to jump into the conduction band of activated CeO2 resulting in increase
in the conductivity of the film The drastic increase in conductivity of the sensor
could be attributed to the adsorptionndashdesorption mechanism resulted from the
electronic defects [26]
5310 Catalytic Activity
The utility of this catalytic system deprotection of several oximes were
studied (Table 52) The catalyst was also tested for reusability and it was found
that it could be reused without loss of initial activity for at least four cycles [19]
TLC analysis indicated the formation of only one product of corresponding
carbonyls FT-IR and NMR analysis showed that the oximes were converted into
carbonyls For checking the reusability (after each run) the catalyst was recovered
by simple filtration and washed several times with acetone and then dried at
373 K The catalyst thus obtained was used for the subsequent runs without any
further modification both activated and deactivated oximes were oxidized in better
yield more than ZrO2 catalyst as shown in Table 52
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
178
Table 52 Oxidative Deoximation of Carbonyls on CeO2
Entry
Substrate
Product
Time
(h)
Yield
()
1
NOH
O
15
62
2
NOH
Cl
O
Cl
15
58
3
NOH
O
25
73
4
NOHCl
OCl
40
57
5
NOH
Cl
O
Cl
30
59
Solvent- Ethyl acetate Catalyst- ZrO2 Temperature- 353 K
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
179
5311 Adsorption of Rhodamine B (Rh B)
The removal of dye pollutants are also of great importance for wastewater
treatment Rhodamine B a common cationic dye used in textile industry is one of
the most notorious contaminants in aquatic environments because of it huge
amounts slow biodegradation and toxicity In this study synthesized CeO2
nanocrystals are further used to remove Rh B The absorption spectrum of Rh B
solution was characterized by its characteristic absorption at 555 nm which was
attributed to the chromophore containing azo linkage of the dye molecules [22]
Fig 518 Absorption spectra of aqueous solution of Rh B in the presence of CeO2
nanocrystals at different times
UV-Visible absorption spectra represented in Fig518 confirms that over 93 of
Rh B in 100 mL of 20 mg L-1
Rh B aqueous solution could be removed with 100
mg of the as-prepared CeO2 nanocrystalline within 60 min The reasons may
account for the efficient removal of Rh B with CeO2 nanocrystals The first reason
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
180
should be their to facilitate the adsorption of Rh B The second one is attributed to
the oxygen vacancies on the surface of CeO2 nanocrystals These abundant surface
oxygen vacancies could produce strong electrostatic attraction with the cationic
groups of Rh B as well as hydrogen bonding with the nitrogen atoms of Rh B
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
181
Conclusions
Microwave synthesis is very beneficial to find a fast simple and energy
efficient approach to produce fine CeO2 nanoparticles It is relatively new method
to produce inorganic compounds for materials processing to enhance the material
properties as well as economic advantages through energy saving and acceleration
of product development Cerium oxide has outstanding physical and chemical
properties therefore it is used as LPG sensor In the area of catalysis nanoparticles
of ceria have been studied Also it is concluded as
1] The CeO2 nanoparticles were prepared by simple microwave assisted sol-gel
method
2] The well spherical and narrow size distribution with 10 nm size particles were
obtained by this method
3] It is very simple time as well as energy saving technique
4] The XRD pattern shows the CeO2 nanoparticles exists in face centered cubic
5] Scanning electron micrographs indicates that grains are uniformaly distributed
6] Transmission electron micrographs indicates that the mean diameter of the
particles as measured is about 10 nm
7] The conductivity of nano CeO2 thick film is represents the almost linear
relationship was found in the measured temperature range of 200-5000C It is
clear that the conduction in crystalline ceria is essentially an n-type electronic
process
8] The CeO2 nanoparticles in the thick film form prepared by screen printing
technique showed better response to LPG gas at 250degC temperature at 600 ppm
concentration of LPG gas
9] Catalyst can be prepared from inexpensive precursors using the microwave
assisted sol-gel technique is promising for the oxidative regeneration of ketones
10] This study reveals that these CeO2 nanocrystals are novel adsorbents for
wastewater treatment
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
182
References
[1] A Ramesh H Hasegawa T Maki KUeda Sep Purif Tech
56 (2007) 90
[2] C Lettmann K Hildenbrand H Kisch W Macyk W F Maier
Appl Catal B 32 (2001) 215
[3] X Zhang Z H Ai F L Jia L Z Zhang J Phys Chem C 112 (2008) 747
[4] N Du H Zhang BD Chen X Y Ma D RYang J Phys ChemC
111 (2007) 12677
[5] F Zhang S Yang H Chen X Yu Cera Intern 30 (2004) 997
[6] F Gu SF Wang MK Lu GJ Zhou D Xu DR Langmuir J SciIR Iran
20 (2004) 3528
[7] H Xiao Z Ai L Zhang JPhys Chem 113 (2009) 16625
[8] L Combemale G Caboche D Stuerga D Chaumont MicroRese
Bull 40 (2005) 529
[9] M Zawadzki Jof Alloys and Comp 454 (2008) 347
[10] A V Patil C G Dighavkar S K Sonawane S J Patil R Y Borse
Sens and Transducers 108 (2009) 189
[11] AV Patil CG Dighavkar RY Borse Sens and Transducers
101 (2009) 96
[12] AV Patil CG Dighavkar SK Sonawane S J Patil RY Borse Sensand
Transducers 9 (2010) 11
[13] DR Patil LA Patil Talanta 77 (2009)1409
[14] R S Blackburn Environ Sci Tech 38 (2004) 4905
[15] GNaja CMustin JBerthelin BVolesky J Colloide Inter Sci
292 (2005) 537
[16] VKGupta IAli Environ Sci Tech 42 (2008) 766
[17] A Mittal VK Gupta A Malviya and JMittal J Hazard Mater
151 (2008) 821
[18] VKGupta IAli VKSaini J Colloid Interface Sci 315(2007) 87
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
183
[19] S S Deshpande S U Sonavane R V Jayaram Cat Com 9 (2008) 639
[20] KM Garadkar BS Shirke YB Patil D R Patil Sens and Transducers
110 (2009) 17
[21] VKGupta AMittal VGajbe JMittal J Colloid Inter Sci
319 (2008) 30
[22] T A Khan I Ali V V Singh S Sharma J Envir Protec Sci 3 (2009)11
[23] A Hosseinnia M Keyanpour-Rad M Pazouki World Applied Sci J
8 (2010) 1327
[24] MI Baraton L Merhari J Am Ceram Soc 75 (2004) 1587
[25] CWang B Xu XWang J Zhao J Solid State Chem 178 (2005) 3500
[26] H Xiao Z Ai L Zhang J Phys Chem C doi 10 1021 JP9050269 (2009)
[27] A M Thompson Oxides of the Rare Earths Wiley New York (1978)
[28] H Noumlremberg G A D Briggs Phys Rev Lett 79 (1997) 4222
[29] A Hosseinnia M Keyanpour-Rad M Pazouki World Appl Sci J
8 (2010) 1327
[30] BD Cullity SR Stock Elements of X-Ray Diffraction 3rd edn
(Prentice Hall Upper Saddle River NJ) (2001) 07458
[31] G Ranga Rao B Gopal Mishra Bul Cat Soc of Ind 2 (2003)122
[32] A K Bhattacharyal T K Naiya S N Mondal S K Das Chem Eng J
137 (2008) 529
[33] G Liu J A Rodriguez Z Chang J Hrbek C H F Peden
J Phys Chem B 108 (2004) 2931
[34] P F Ji J L Zhang F Chen M Anpo J Phys Chem C 112 (2008) 17809
[35] A Trovarelli Catal Rev SciEng 38 (1996) 439
[36] B Li D M Pan J S Zheng Y J Cheng X Y Ma F Huang L Zhang
Langmuir 24 (2008) 9630
[37] M Fernaacutendez-Garcıacutea A A B Martıacutenez-Arias A Hungrıacutea Iglesias-Juez
J C Conesa J Soria J Phys Chem Chem Phys 4 (2002) 2473
[38] H M Chen J H He J Phys Chem C 112 (2008) 17540
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
184
[39] F Zhang S Chan W Spanier J E Apak E Jin Q Robinson
R D Herman I P Appl Phys Lett 80 (2002) 127
[40] G Adachi TMasui In Catalysis by Ceria and Related Materials
ATrovarelli Ed Imperial College Press London (2002)
[41] J A Rodriguez X Wang J C Hanson G Liu A Iglesias-Juez
MFernaacutendez-Garcıacutea J Chem Phys 119 (2003) 5659
[42] S Eck C Castellarin-Cudia S Surnev M G Ramsey F PNetzer
Surf Sci 520 (2002) 173
[43] R B Yu L Yan P Zheng JChen X X R J Phys ChemC
112 (2008) 19896
[44] Y Nagai T Yamamoto T Tanaka SYoshida T Nonaka T Okamoto
A Suda M Sugiura Catal Today 74 (2002) 225
[45] Y M Chiang E B Lavik I Kosacki H L Tuller JY Ying
J Electroceram 1 (1997) 7
[46] D R Patil L A Patil G H Jain M S Wagh S A Patil
Sens and Transducers 74 (2006) 874
[47] K Sohlberg S K Pantelides S J Pennycook J Am Chem Soc
123 (2001) 6609
[48] L S Zhong J S Hu A M Cao Q Liu W G Song LWan
J Chem Mater 19 (2007) 1648
[49] J B Fei Y Cui X H Yan Y Yang K W Wang QHe J B Li
AdV Mater 20 (2008) 452
[50] P V Kamat J Phys Chem B 106 (2002) 7729
[51] R D Robinson J E Spanier F Zhang SW Chan I P Herman J Appl
Phys 92 (2002) 1936
[52] S W Cao Y J Zhu J Phys Chem C 112 (2008) 6253
[53] R Georgekutty M K Seery S C Pillai J Phys Chem C
112 (2008) 13563
[54] J S Hu L S Zhong W G Song L J Wan Adv Mater 20 (2008)1
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
Chapter ndash V
185
[55] HXu F L Jia Z H Ai L Z Zhang Cryst Growth Des (2007)
[56] H M Jia W J Xiao L Z Zhang Z F Zheng J PhysChem C
112 (2008) 1379
[57] Z H Ai H Y Xiao T Mei J Liu L Z Zhang K J Deng J R Qiu
J PhysChem C 112 (2008) 11929
[58] L M Ma W X Zhang EnViron Sci Technol 42 (2008) 5384
[59] Z H Ai Y Chen L Z Zhang J R Qiu EnViron Sci Technol
42 (2008) 69550
[60] Z Y Zhong J Ho J Teo S C Shen AGedanken ChemMater
19 (2007) 4776
[61] S C Kuiry S D Patil S Deshpande S Seal J Phys ChemB
109 (2005) 6936
[62] D R Patil L A Patil Sens IEEE 7 (2007) 434
[63] P Jasinski Anderson H U Sens Actuators B 95 (2003) 73
[64] J P Nair E Wachtel I Lubomirsky J Fleig JMaier AdVMater
15 (2003) 2077
[65] R J Qi Y J Zhu G F Cheng Y H Huang Nanotechnology
16 (2005) 2502
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