Study the Photodegradation of Aniline Blue dye in … · Advanced oxidation processes are of ample...
Transcript of Study the Photodegradation of Aniline Blue dye in … · Advanced oxidation processes are of ample...
International Journal of Engineering & Technology IJET-IJENS Vol:13 No:04 26
N SI J E IJENS © August 2013 IJENS -IJET-6262-043311
Study the Photodegradation of Aniline Blue dye in
Aqueous Phase by using Different Photocatalysts
Hanaa Kadtem Egzar, Muthana Saleh Mashkour and Amer Muosa Juda Chemistry Department, College of Science,
Kufa University, Najaf, Iraq.
Abstract-- This study involves the photocatalytic
degradation of Aniline blue(AB) dye, employing heterogeneous
photocatalytic process. Photocatalytic activity of different
semiconductors such as zinc oxide (ZnO) ,zinc sulfide (ZnS)
and Tin dioxide (SnO2) has been investigated. An attempt has
been made to study the effect of process parameters through
amount of catalyst, concentration of dye, pH of dye solution
and temperature on photocatalytic degradation of AB solution.
The experiments were carried out by varying pH (2-12),
amount of catalyst (0.05–1.5 g), initial concentration of dye
(25–100ppm ) and temperature range(293-323)K. The
optimum catalyst dose was found to be( 0.1 ,0.5 g and 1) g\L by
using ZnO ,ZnS and SnO2, respectively. In the case of ZnO and
SnO2 , maximum rate of photoreaction of AB solution was
observed in acidic medium at pH 4, whereas the degradation of
AB reached maximum at pH 5 when using ZnS catalyst . The
performance of photocatalytic system employing ZnO/UV light
was observed to be better than ZnS /UV and SnO2/UV system.
The complete degradation of AB was observed after 12 min
with ZnO, whereas with ZnS, only 75% dye degraded and
24.5% with SnO2in 12 min. Photocatalytic degradation was
found to increase with increasing temperature. Arrhenius plot
shows that the activation energy is equal to 20.94 kJ mol−1 with
ZnO, 17.97 kJ mol−1 with ZnS and 14.1 mol−1 with SnO2
catalyst. The thermodynamic parameters of the
photodegradation of AB, like energy of activation, enthalpy of
activation, entropy of activation and free energy of activation
revealed the efficiency of the process.
Index Term-- Decolorization; Triphenylmethane; Aniline
blue ; Photocatalysis
1. INTRODUCTION
The treatments of industrial wastewater for aqueous
waste effluents include different techniques such as
biological treatment, reverse osmosis and activated carbon
adsorption.(1)
These techniques often utilize potentially
hazardous or polluting materials and even most of them are
non-biodegradable.(2)
Therefore, the development of an
effective treatment technique that can convert pollutants into
non-toxic or less harmful materials is highly required.
Advanced oxidation processes are of ample interest
currently for the effective oxidation of a wide variety of
organics and dyes(3)
. Advanced Oxidation Processes (AOP)
are an attractive alternative for the treatment of
contaminated ground, surface, and waste waters containing
hardly-biodegradable anthropogenic substances as well as
for the purification and disinfection of drinking waters(4)
.
Photocatalysis is a phenomenon that occurs when a reaction
chain is taking place in the presence of light and solid
catalyst in the solution(5)
. Photocatalyst is also called photochemical catalyst and
the function is similar to the chlorophyll in the
photosynthesis. In a photocatalytic system, photo-induced
molecular transformation or reaction takes place at the
surface of catalyst Schematic( 1).The initial step of
photocatalysis is the adsorption of photons by a molecule to
produce highly reactive electronically excited states. The
photon needs to have energy of (hυ) equal to or more than
the band gap energy of the semiconductor. The energy
absorbed will cause an electron to be excited from the
valence band to the conduction band, leaving a positive hole
in the valence band. This movement of electrons forms (e-
/h+) or negatively charged electron/positively charged hole
pairs . The positively charged holes in valence band are
powerful oxidants, whereas the negatively charged electrons
in conduction band are good reductants(5)
.
Schematic. 1. Mechanism of radical formation reactions during
photocatalytic process as a results of photocatalyst excitation with light (6)
Following are the reactions involving in photocatalysis:-
Concerning photocatalysis with photocatalyst, electrons in
conduction band (ecb
-
) and holes in the valence band (hvb
+
)
are produced when the catalyst is irradiated with light
energy higher than its band gap energy Ebg
(hν>Ebg
).
TiO2
+ hν (UV< 400nm) → TiO2 (e
cb
-
+ hvb
+
) (1)
hvb
+
+ H2O → h
+
+ HO (2)
hvb
+
+ HO-
→ HO (3)
Organic molecule +hvb
+
→ oxidation products (4)
ecb
-
+ O2 → O
2
-
(5)
O2
-
+ h+
→ HO2
(6)
Organic molecule +ecb
-
reduction products (7)
HO,
HO2
+ organic compounds → degradation products
(8)
Semiconductor compounds have drawn much attention
during the last few years because of their novel optical and
transport properties which have great potential for many
optoelectronic applications.(7)
International Journal of Engineering & Technology IJET-IJENS Vol:13 No:04 27
N SI J E IJENS © August 2013 IJENS -IJET-6262-043311
Among the listed semiconductors, TiO2 has proven to be
the most suitable for widespread environmental applications.
ZnO also seems to be a suitable photocatalyst but it
dissolves in acidic solutions it is a semiconductor material
for various photonic and electrical applications. ZnO shows
a unique set of physical and chemical properties, such as a
wide band gap (3.2 eV), large exaction binding energy (60
meV) at room temperature, radiation hardness(8)
.
Tin dioxide (SnO2) is a n-type semiconductor with a large
band gap (Eg = 3.9 eV ) which shows promise for a number
of applications including transparent conductors.
Zinc sulfide (ZnS) is a wide band gap and direct transition
semiconductor(9)
. Zinc sulfide is an important semiconductor
material with a wide direct band gap Eg = 3.68 eV (10)
.
Dyes are typically organic compounds that absorb light
in specific areas of the visible spectrum. Aniline Blue dye it
is water soluble dye(11)
, it is used for dying wool and cotton
directly and widely used in dye industries therefore its
presence in the industrial discharge water also contributes to
environmental pollution(12)
. Due to its stability , it has long
residence time in water.(13)
Molecular structure of Aniline
Blue has been illustrated in Fig. 1. Aniline Blue, also called
acid blue 22, china blue, soluble blue 3M, and Marine blue.
It is very soluble in water,
Fig. 1. structure of Aniline Blue dye(14).
Aniline Blue dye is a acidic dye belongs to
triphenyl methane class of dye(15)
Triphenylmethane dyes are
those dyes in which a central carbon atom is bonded to two
benzene rings and one p-quinoid group (chromophore)(16)
.
The auxochromes are - NH2, NR2 and –OH(17)
.
Triphenylmethane dyes are used extensively in the textile
industries for dyeing of nylon, polyacrylon nitrile, modified
nylon, wool, silk and cotton.
In recent years, problem of wastewater became very
important both for the sake of increasing amount and its
variety . Removing color from waters is often more
important than other colorless organic substances, because
the presence of small amounts of dyes is clearly visible and
influence the water environment considerably. This work
reports an investigation of the photocatalytic degradation of
aniline blue dye using different types of catalyst ZnO, SnO2,
and ZnS. The effect of different parameters was studied to
estimate the best condition for degradation of aniline blue
dye; and these parameters were the amount of catalyst, dye
concentration, pH of dye solution and temperature of
reaction and this is to prevent the expansion of colored
pollution in our environments.
2. EXPERIMENTAL
A homemade photoreactor equipped with a Philips
250W, medium pressure mercury lamp as a source for UV
radiation, was used to determine P.D.E. The reactor was
consisted of graduated 1000 cm3 Pyrex glass beaker and a
magnetic stirring setup. The lamp was positioned
perpendicularly above the beaker. The distance between the
lamp and the graduated Pyrex glass was 15 cm. The whole
photocatalytic reactor was insulated in a wooden box to
prevent the escape of harmful radiation and minimized
temperature fluctuations caused by draughts. Zinc oxide with 99% purity were supplied by Fluka-
Garantie, Zinc sulfide with 99.3% purity supplied by
M.B.LTD Dagenham and Tin dioxide SnO2 with 99% purity
was supplied by Fluka-Garantie . Aniline blue dye
(analytical grade) was purchased from (RDS-Hannover) and
used without further purification. Solutions were prepared
using double distilled water. In all experiments, the required
amount of the catalyst was suspended in 200 cm3 of aqueous
solutions of AB, using a magnetic stirrer. At predetermined
times; 5 cm3 of reaction mixture was collected and
centrifuged (3000 rpm, 15 min) in centrifuge. The
supernatant was carefully removed by a syringe with a long
pliable needle and centrifuged again at same speed and for
the same period of time. This second centrifugation was
found necessary to remove fine particles of catalysts. After
the second centrifugation the absorbance at (309, 586) nm of
the supernatants was determined using ultraviolet-visible
spectrophotometer, type UV-1650pc.
P.D.E. of AB was followed spectrophotometrically by a
comparison of the absorbance, at specified interval times,
with a calibration curve accomplished by measuring the
absorbance, at λ max (586) nm, with different concentrations
of the dye solution.
%Decolorization = 100 × (C0 − C)/C0
where C0 = initial concentration of dye solution, C =
concentration of dye solution after photoirradiation. In order
to determine the effect of catalyst loading, the experiments
were performed by varying catalyst concentration from 0.05
to 1.5 g for dye solutions of 100ppm at natural pH (5.57).
Similar experiments were carried out by varying the pH of
the solution pH( 2–12) and concentration of
dye(25,50,75,100 )ppm. the reaction temperatures amounted
to (293- 323)K.
3. RESULTS AND DISCUSSION
3.1. UV–vis spectra of dye
Results of the present study clearly show that the
photocatalytic treatment of aqueous solution of aniline blue
under UV light, leads to decolorization and degradation of
dye. Figs.2 to 4 shows the typical time dependent UV-Vis
spectrum of AB solution during photoirradiation with ZnO,
ZnS andSnO2 respectively. The rate of degradation was
recorded with respect to the change in the intensity of
absorption peak in ultraviolet region and visible region. The
prominent peaks were observed at λmax(586) nm which
decreased gradually and finally disappeared indicating(18)
that the dye had been degraded.
International Journal of Engineering & Technology IJET-IJENS Vol:13 No:04 28
N SI J E IJENS © August 2013 IJENS -IJET-6262-043311
Fig. 2. Time dependent UV-Vis absorption spectra for degradation of
aniline blue dye(100ppm) ,(0.1g) ZnO catalyst, time(min).
Fig. 3. Time dependent UV-Vis absorption spectra for degradation of
aniline blue dye(100ppm),(0.5g) ZnS catalyst, time(min).
Fig. 4. Time dependent UV-Vis absorption spectra for degradation of
aniline blue dye (100ppm),(1.0g) SnO2catalyst,time(hours) .
Fig 5 show the comparison of the reactivity of different
types of catalyst. The results show that the rate constant of
degradation of aniline blue solution in the presence of ZnO
is more rapid than the other catalysts because of the small
band gap(3.2eV) of ZnO. The results shown in Fig. 5 are in
good agreement with those published by many research such
as study photocatalytic activity of different semiconductors
such as SnO2, ZrO2, CdS, and ZnO (19-22)
. Kansal et al(19)
.
compared the photocatalytic activity of TiO2, ZnO, SnO2,
ZnS, and CdS for the decolorization of methyl orange and
rhodamine 6G dyes and found ZnO to be the most effective
catalyst for the decolorization of dyes. Lizma et al. (21)
reported the photocatalytic decolorization of Reactive Blue
19 (RB-19) in aqueous solutions containing TiO2 or ZnO as
catalysts and concluded that ZnO is a more efficient catalyst
than TiO2 in the color removal of RB-19.This means
promoting the electrons from the valance band to
conduction band which needs low energy. On the other hand
SnO2 exhibits less activity because their wide band gap
(3.9eV)and light energy are not sufficient to excite this
catalyst.(23)
By using SnO2 the other part of light with energy
which is less than the band gap of illuminated
semiconductor will be decolorized by the adsorbed dye
molecules. Dye molecules will be decolorized by a
photosensitization process.
Fig. 5. The change of P.D.E with irradiation time of different types of
catalyst .
3.2Degradation of AB solution Under Different
Experimental Conditions
Degradation of AB solution was investigated under
seven different experimental conditions through UV alone,
UV + ZnS, UV + ZnO,UV+ SnO2, Dark + ZnS , Dark +
ZnO and Dark + SnO2. Fig.6 depicts the photocatalytic
degradation of AB solution under these experimental
conditions. Initially blank experiments were performed
under UV irradiation without addition of any catalyst (UV
alone) and only 10% degradation was observed after 60min.
Fig. 6. Photocatalytic degradation of AB dye (dye initial concentration—
100ppm, (0.1g)ZnO,(0.5g)ZnS ,(1g) SnO2 after 12min.
Thereafter the adsorption of the dye was observed with
both catalysts, i.e., Dark + ZnS, Dark+ SnO2 and Dark +
ZnO. Only 14.3%, 32% and 7.7respectively adsorption of
the dye was seen in the same time with both catalysts under
dark conditions. Then photocatalytic experiments were
carried out using all catalysts at fixed dye concentration
(100ppm) and catalyst amount of 0.1g of ZnO ,0.5g of ZnS
and1g of SnO2. When experiments were performed under
UV irradiation with ZnO as photocatalyst (UV + ZnO), the
complete degradation of dye was achieved after 12 min,
whereas with ZnS as a photocatalyst (UV + ZnS), only 75%
0
20
40
60
80
100
120
0 5 10 15
ZnOZnSSnO2
P.D.E
Time(min
0
20
40
60
80
100
P.D.E
International Journal of Engineering & Technology IJET-IJENS Vol:13 No:04 29
N SI J E IJENS © August 2013 IJENS -IJET-6262-043311
decolorization of AB solution was observed and only 24.3%
byusingSnO2in the same duration. It indicates that ZnO
exhibits higher photocatalytic activity than other
semiconductors for the decolorization of AB dye.
3.3Degradation of Dye by ZnO, SnO2 and ZnS as
Photocatalysts
The experiments were carried out to study the
degradation of AB solution employing ZnO, ZnS , SnO2 as
catalysts under UV light. Various parameters which affect
the degradation efficiency such as catalyst loading (0.05–
1.5) g, pH (2-8), initial concentration of dye (25–100) ppm,
and temperature (293-323)K of degradation were assessed
under UV light.
3.3.1Effect of Catalyst weight
Fig. 8 show the effect of ZnO, ZnS and SnO2 catalyst
amount on the degradation of AB solution at natural pH. It
can be seen that initial slopes of the curves increase greatly
by increasing catalyst weight from 0.05 to 0.1 g for ZnO ,
to 0.5g for ZnS, and to1g for SnO2 thereafter the rate of
degradation remains constant or decreases. Further increase
in the dose of catalyst had no effect on degradation of dye.
The photocatalytic destruction of other organic pollutants
has also exhibited the same dependency on catalyst dose .
This can be explained on the basis that optimum catalyst
loading is found to be dependent on initial solute
concentration because with the increase in catalyst dosage,
total active surface area increases, hence availability of more
active sites on catalyst surface(18)
. At the same time, due to
an increase in turbidity of the suspension with high dose of
photocatalyst, there will be decrease in penetration of UV
light and hence photoactivated volume of suspension
decreases(24)
. Thus it can be concluded that higher dose of
catalyst may not be useful both in view of aggregation as
well as reduced irradiation field due to light scattering(25)
.
Fig. 7. Effect of ZnO ,ZnS and SnO2 dose on degradation efficient of AB dye (at natural pH(5.57), and initial concentration of dye 100ppm),after
(12min)
3.3.2Effect of pH
Wastewater containing dyes is discharged at different
pH; therefore it is important to study the role of pH on
degradation of dye. In order to study the effect of pH on the
degradation efficiency, experiments were carried out at
various pH values, ranging from 2 to 12 for constant dye
concentration (100) ppm and catalyst weight (0.1,0.5 and 1
g for ZnO, ZnS and SnO2, respectively). Fig.8 show the
photodegradation efficiency of AB solution as a function of
pH. It has been observed that by using ZnO and SnO2, the
degradation efficiency increases with increase in pH
exhibiting maximum rate of degradation at pH . In the case
of ZnS, the maximum degradation was observed at pH 5.
Similar behavior has also been reported for the
photocatalytic efficiency of ZnS for decolorization of acid
dyes. The interpretation of pH effects on the efficiency of
the photocatalytic degradation process is a very difficult
task, because of its multiple roles. First, it is related to the
acid base property of the metal oxide surface and can be
explained on the basis of zero point charge(26)
. The
adsorption of water molecules at sacrificial metal sites is
followed by the dissociation of OH− charge groups, leading
to coverage with chemically equivalent metal hydroxyl
groups (M-OH)(27)
. Due to amphoteric behavior of most
metal hydroxides, the following two equilibrium reactions
are considered (Eqs. 9 and 10).
M-OH + H+ M-OH2
+ (9)
M-OH M-O- +H
+ (10)
Fig. 8. Effect of pH on degradation rate of AB dye (ZnO dose—0.1 g, ZnS
dose—0.5 g and 1.0gSnO2 ,dye initial concentration100ppm ).
The zero point charge (zpc) for ZnO is 9 and 6.7for ZnS,
surface is positively charged below this point and above this
pH, surface is negatively charged by adsorbed
OH−ions
(28).photocatalytic activity of anionic dyes (mainly
sulfonated dyes) such as AB dye reaches a maximum value
in lower zero point charge. At pH > zpc, the surface is
positively charged and the dye is anion(29)
. The experimental
results revealed that higher degradation of AB solution was
found to be in acidic conditions. This may be attributed to
the electrostatic interactions between the positive catalyst
surface and dye anions leading to strong adsorption of the
latter on the metal oxide support(30)
.
3.3.3Effect of Concentration of Dye
After optimizing the pH conditions and catalyst dose
(pH 4 and catalyst dose 0.1 g for ZnO, pH 5 and catalyst
dose 0.5 g for ZnS, pH 4 and catalyst dose 1 g for SnO2), the
photocatalytic degradation of dye was carried out by varying
the initial concentrations of the dye (25- 100) ppm in order
to assess the appropriate amount of catalyst dose. As the
concentration of the dye was increased, the rate of
photoreaction decreased indicating for either to increase the
catalyst dose or time span for the complete removal.
Fig.9depict the time-dependent graphs of degradation of AB
0
20
40
60
80
100
120
0 0.5 1 1.5 2
ZnOZnSSnO2
P.D.E
weight(
0
20
40
60
80
100
120
0 5 10
ZnO
ZnS
SnO2
P.D.E
pH
International Journal of Engineering & Technology IJET-IJENS Vol:13 No:04 30
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solution at different concentrations of dye . The possible
explanation for this behavior is that as the initial
concentration of the dye increases, the path length of the
photons entering the solution decreases and in low
concentration the reverse effect is observed, thereby
increasing the number of photon absorption by the catalyst
in lower concentration(31,32)
.
Fig. 9. Effect of initial concentration of AB dye on photodegradation
efficiency when using (ZnO dose0.1g, pH 4, ZnS dose0.5g and1.0g SnO2, pH 5.57 )
3.3.4 Effect of temperature: The photocatalytic degradation was studied at various
temperatures in the range (293–323)K and rate constant, k,
was determined from the first-order plots. An increase in
temperature helps the reaction to compete more efficiently
with e–/H+ recombination(33)
. The energy of activation, Ea,
was calculated from the Arrhenius plot of ln k vs. 1/T (figure
10). Arrhenius plot shows that the activation energy for
photocatalytic degradation of AB solution is equal to(
20±1,17±1 and14±1) kJ mol-1
by using ZnO ,ZnS and SnO2
respectively. The experimental activation energy was
associated with the energy required to promote
photoelectron from trapping centers into tin dioxide
conduction band. the present value probably arises from the
surface area and the purity of catalysts(34)
.
Fig. 10. Arrhenius plot for photocatalytic degradation of AB on ZnO , ZnS
and SnO2 catalysts.
The other thermodynamic parameters such as Enthalpy of
activation ΔH#, entropy of activation ΔS
# and free energy of
activation ΔG# were calculated from equations
(29) :
lnA =ln
+
(11)
lnA= intercept
KB: Boltzmann constant = 1.38066 10-23 J K-1
R: universal gas constant = 8.31441 J mol-1K-1
h: Planck constant = 6.6262 10–34 J s
The Enthalpy of activation (ΔH#) was calculated from
equation(35)
:
ΔH#=Ea-RT (12)
The free energy of activation(ΔG#) was calculated from
equation:
ΔG#=ΔH
#- TΔS
# (13)
The positive ΔH# refer to endothermic reaction , the
positive ΔG# obtained indicate that the reaction is non
spontaneous . Fairly high positive ΔH# and ΔG
# this could
be because the activated state is a well solvated structure
formed between the dye molecules and the reaction
intermediates that is hydroxyl radicals which is also
supported by negative entropy of activation. In the present
case the value of ΔS# is negative as in Tables 1,2 and 3 , so
that the complex formed is more ordered than the reactants .
Initially the complex formed is unstable and degradation of
the reactants into products is not very slow, but takes place
rapidly under present experimental conditions(36)
.
0
20
40
60
80
100
120
0 50 100 150
ZnO
con.(pp
P.D.E
-5
-4
-3
-2
-1
0
2.8 3 3.2 3.4 3.6
ZnOZnSSnO2
International Journal of Engineering & Technology IJET-IJENS Vol:13 No:04 31
N SI J E IJENS © August 2013 IJENS -IJET-6262-043311
Table I
values of kinetics and thermodynamic parameters for the photocatalytic degradation of AB solution by using ZnO .
T(k) K(min-1
) Ea(KJ mol-1
) ΔH(KJ mol-1
) ΔS(KJ. mol-1
.K-1
) ΔG(KJ mol-1
)
293 0.338232
21.34
18.90
-0.245
90.68
303 0.450890 18.82 93.05
313 0.671432 18.73 95.41
323 0.950917 18.65 97.78
Table II
Values of kinetics and thermodynamic parameters for the photocatalytic degradation of AB solution by using ZnS .
T(k) K(min-1
) Ea(KJ mol-1
) ΔH(KJ mol-1
) ΔS(KJ. mol-1
) ΔG(KJ mol-1
)
293 0.16528
17.8
15.36
-0.252
89.9
303 0.21054 15.28 91.6
313 0.27060 15.19 94.06
323 0.36505 15.11 96.5
Table III
Values of kinetics and thermodynamic parameters for the photocatalytic degradation of AB solution by using SnO2.
T(k) K(min-1
) Ea(KJ mol-1
) ΔH(KJ mol-1
) ΔS(KJ. mol-1
.K-1
) ΔG(KJ mol-1
)
293 0.017087
15.64
13.21
-0.272
92.9
303 0.021130 13.12 95.5
313 0.025370 13.04 98.2
323 0.032381 12.6 100.7
3.3.5Kinetic Study
Figure 11 show the kinetics of disappearance of AB for
an initial concentration of 100ppm under optimized
conditions. The results show that the photocatalytic
degradation of dye in aqueous ZnO , ZnS and SnO2 can be
described by the first-order kinetic according to the
Langmuir–Hinshelwood model(37-39)
, ln (C/C0) =- kt, where
C0 is the initial concentration and C is the concentration at
any time, t. The semi-logarithmic plots of the concentration
data gave a straight line. The rate constants were calculated
to be (0.338232, 0.165280 and 0.017087) min-1
for ZnO ,
ZnS, and SnO2 respectively.
Fig. 11. Kinetics analysis for AB dye (dye initial concentration100ppm),
(0.1g ZnO), (0.5g ZnS) , and 1.0gSnO2.
4. CONCLUSION
The results of this study demonstrate that comparison
of photocatalytic activity of different semiconductors has
clearly indicated that the ZnO is the most active
photocatalyst for degradation of aniline blue dye solution.
Moreover, photocatalytic activity of ZnO is greater in the
presence of UV light. The initial rate of photodegradation
increased with the increase of the catalyst dose up to an
optimum loading. Increasing weights of catalysts is
attributed to the increase of the availability of photocatalysts
sites further increase in catalyst dose showed no effect. As
the initial concentration of dyes was increased, the rate of
degradation decreased in dye due to the decrease of the
concentration OH- adsorbed on catalyst surface. The
increasing of dye concentration increases the competitions
between OH- and dye to adsorb on active site of catalyst.
Photocatalytic activity of anionic dyes (AB) reaches a
maximum value in lower zero point charge. At pH > zpc, the
surface is positively charged and repels R-SO3 - ions.
The photocatalytic decolorization and degradation
followed pseudo-first order kinetics according to the
Langmuir–Hinshelwood model.
The temperature is the factor that has the smallest effect
on the photocatalytic degradation of AB solution ,Ea, which
0
2
4
6
8
10
12
14
0 10 20 30
ZnO
ZnS
SnO2
lnCC
0
International Journal of Engineering & Technology IJET-IJENS Vol:13 No:04 32
N SI J E IJENS © August 2013 IJENS -IJET-6262-043311
was found to be smaller than 40 kJ mol−1
.The results
illustrate the decoloration of AB dye is mainly physical
interaction. The thermodynamic parameters of the
degradation of AB solution have been reported. The positive
ΔH# refer to endothermic reaction , the positive ΔG
#
obtained indicate that the reaction is non spontaneous .
Fairly high positive ΔH# and ΔG
# this could be because the
activated state is a well solvated structure formed between
the dye molecules and the reaction intermediates that is
hydroxyl radicals which is also supported by negative
entropy of activation. Initially the complex formed is
unstable and degradation of the reactants into products is not
very slow, but takes place rapidly under present
experimental conditions.
The controlled experimental indicates that the presence
of UV light, and catalyst are essential for the effective
destruction of aniline blue solution.
Future research is needed for the development of more
efficient catalysts for harnessing solar energy which are low
cost and effective. Designing of reactors and solar collectors
for photocatalytic treatment needs to be developed so that
they can be used by both small and large scale textile
industries in combination with the existing technology
ultimately leading to recycling of water as large amount of
water is utilized in textile industry.
5. SUGGESTED MECHANISM
Fig. 13. Suggested mechanism of photodegradation of Aniline blue dye.
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