Post on 22-Sep-2020
Research ArticleAgAgCl Loaded Bi2WO6 Composite A Plasmonic Z-SchemeVisible Light-Responsive Photocatalyst
Xiangchao Meng and Zisheng Zhang
Department of Chemical and Biological Engineering University of Ottawa 161 Louis Pasteur Private Ottawa ON Canada K1N 6N5
Correspondence should be addressed to Zisheng Zhang zzhanguottawaca
Received 16 November 2015 Accepted 24 February 2016
Academic Editor Ying Dai
Copyright copy 2016 X Meng and Z Zhang This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
Hierarchical flower-like Bi2WO6was successfully synthesized by facile hydrothermal method at low pH And AgAgCl was loaded
by photoreduction on its surface As-prepared photocatalysts were characterized by various techniques Bi2WO6was successfully
synthesized at a size of 2-3 120583mDepositingAgAgCl did not destroy the crystal structure and bothAg+ andmetallic Ag0 were foundThe band gap of the composite was 257 eV which indicates that visible light could be the activating irradiation In the photocatalyticactivity test the composite with 10wt AgAgCl boasted the highest removal efficiency (almost 100) in 45min The significantenhancement can be attributed to the surface plasmon resonance (SPR) effect and the establishment of heterostructures betweenAgAgCl and Bi
2WO6 A possible mechanism of photocatalytic oxidation in the presence of AgAgCl-Bi
2WO6was proposed This
work sheds light on the potential applications of plasmonic metals in photocatalysis to enhance their activities
1 Introduction
Surface plasmon resonance (SPR) has been widely appliedin the conversion of solar to chemical energy It may bedescribed as the resonant photon-induced collective oscil-lation of valence electrons when the frequency of photonsmatches the natural frequency of surface electrons oscillatingagainst the restoring force of positive nuclei [1] The wave-length of a resonant photon depends on the type of metalFor silver nanoparticles surface electrons may be activatedby ultraviolet (UV) and visible (Vis) photons
AgAgCl was first reported by Wang et al to exhibit anexcellent photocatalytic activity due to the SPR effect [2]Thisstudy shed light on the potential implementation of AgAgClfor the photocatalytic oxidation of organic pollutants To dateresearchers have designed composites by depositing AgAgClon photocatalysts such as AgAgCl-TiO
2[3 4] andAgAgCl-
BiOX (X=Cl Br) [5] aiming to enhance their performancesMeanwhile numerous novel photocatalytic materials havealso been reported Among these materials Bi
2WO6 with a
band gap of 270 eV has been found to exhibit a high visible-light-driven photocatalytic activity with regard to the degra-dation of organic contaminants [6]This is due to the valence
band of bismuth-based photocatalysts consisting of not onlyO 2p orbits but also Bi 6s orbits It has been confirmed thatmoderately well-dispersed orbits are able to accelerate themobilities of photogenerated carriers and narrower band gap[7] However one of themain problems surrounding Bi
2WO6
implemented in the degradation of organic pollutants inwastewater is the high recombination rate of photogeneratedcarriersOne of themost effective approaches to deal with thisissue is to establish heterostructures such as BiOBr-Bi
2WO6
[8 9] WO3Bi2WO6[10 11] and Bi
2O3Bi2WO6[10] At
present there is still no published work establishing theAgAgCl-Bi
2WO6heterostructure applied in the degradation
of organic pollutantsBased on the above analysis depositing AgAgCl on
Bi2WO6should enhance its photocatalytic activity due to
the SPR effect and the heterostructure The depositingmethod (the photoreduction method) can be implementedas reported [12] In this work a facile method of preparing anAgAgCl-Bi
2WO6composite was developed As-synthesized
photocatalysts were investigated in terms of their crystalstructures morphologies optical properties and visible-light-induced photocatalytic activities with regard to thedegradation of the organic contaminant Rhodamine B (RhB)
Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2016 Article ID 4054351 11 pageshttpdxdoiorg10115520164054351
2 International Journal of Photoenergy
Apossiblemechanismof the photocatalytic oxidation processin the presence of the AgAgCl-Bi
2WO6composite was also
explored and proposedThe enhanced photocatalytic activitymay be regarded as solid evidence of the potential applicationof AgAgCl in photocatalytic oxidation processes
2 Experimental
21 Preparation of Bi2WO6and AgAgCl-Bi
2WO6Compos-
ites All of the reagents were purchased from the Sigma-Aldrich Company were of analytical purities and wereused as received Bi
2WO6was synthesized by a hydrother-
mal method In a typical process 09702 g Bi(NO3)3sdot5H2O
were dissolved in 20mL acetic acid termed solution Awhich was magnetically stirred for 10min Next 03298 gNa2WO4sdot2H2O were dissolved in 40mL distilled deionized
water (DDW) termed solution B Solution B was addeddropwise into solution A and stirredmagnetically for 30minThe suspension was then transferred to a 100mL Teflon-linedstainless steel autoclave (approximately 60 of its maximumvolume) and heated at 180∘C for 20 h After the autoclavewas allowed to cool to room temperature the precipitate wasseparated by centrifugation and washed once with ethanoland then twice with DDW The precipitate was then dried at60∘C for 12 h
The AgAgCl-Bi2WO6composite was prepared by the
photoreduction method Typically 032 g Bi2WO6were dis-
persed in 40mL DDW and sonicated for 30min Next 024 gNaCl (excess amount) was added to the suspension whichwas termed solution C Meanwhile 00421 g AgNO
3were
added to 20mL DDW termed solution D Solution D wasadded dropwise to solution C with vigorous stirring for30min Products were separated by centrifugation and dis-persed in 40mL DDW and then illuminated under a 300Whalogen tungsten projector lamp (Ushio) for 30min Finalproducts were separated via centrifugation washed twicewith DDW and dried at 60∘C for 12 h The sample was thencollected and labelled as AgAgCl (10 wt)-Bi
2WO6 Simi-
larly AgAgCl (1 wt)-Bi2WO6 AgAgCl (2 wt)-Bi
2WO6
AgAgCl (4wt)-Bi2WO6 AgAgCl (8 wt)-Bi
2WO6 and
AgAgCl (20wt)-Bi2WO6were also prepared
22 Characterization X-ray diffraction (XRD) analysis wasperformed using a Rigaku Ultima IV Diffractometer withCuK120572 radiation (120582 = 015418 nm) at 40 kV and 44mASurface elements and the chemical states of samples weretested using a XSAM-800 X-ray Photoelectron Spectroscope(XPS) A field-emission scanning electron microscope (FE-SEM JEOL JSM-7500F) using energy dispersive X-ray spec-troscopy (EDS) and transmission electronmicroscopy (TEMJEM-2100F) were applied to explore the morphologies ofsamples Acceleration voltages of the SEM and TEM were300 kV and 200 kV respectively The Thermo Evolution300 spectrophotometer was used to evaluate the ultraviolet-visible (UV-Vis) diffuse reflectance spectra (DRS) of thephotocatalysts
23 Photocatalytic Activity Test The target organic pol-lutant was Rhodamine B (RhB) The characteristic peak
in UV-Vis spectroscopy of RhB is found at a wavelengthof 554 nm which was used to calculate its concentrationbased on the Beer-Lambert law A 500mL beaker with acooling jacket maintaining the system at 20∘C served asthe photocatalytic reactor The visible-light source was a300W halogen tungsten projector lamp (Ushio) with a cut-off (Kenko Zeta transmittancegt 90) to filter out irradiationwith a wavelength below 400 nm The distance between theirradiation source and the top of the beaker was 10 cm andthe irradiation intensity was measured by a quantum meter(Biospherical QSL-2100 400 nm lt 120582 lt 700 nm) to be 11 times10minus2 Einsteinsmminus2 sminus1 In each batch 100mL fresh solutionwith a concentration of RhB at 10mgL (10 ppm) was addedto the reactor and mixed with as-prepared photocatalysts inthe absence of light for 30min to ensure that adsorption-desorption equilibrium was achieved The quantity of photo-catalyst added was 05 gL After mixing the light was turnedon to begin the photocatalytic process An aliquot of 1mLsuspension was taken every 3min for 45min and tested usingaGenysys 10-UV spectrophotometer (Geneq Inc) To explorethe roles of radical species EDTA-2Na and 2-Butanol withconcentrations of 001molL were added to the reactor
To study the degradation of phenol 100mL phenol solu-tion with a concentration of 10mgL (ppm) was mixed withan AgAgCl-Bi
2WO6composite Samples taken during the
photocatalytic processwere tested usingUV-Vis spectroscopywith the peak absorption at a wavelength of 270 nm Otherprocedures used the same process as that of the degradationof RhB
To recycle the photocatalysts photocatalysts were sepa-rated by centrifugation between experiments and then usedin the following experiment without a wash The final usedproducts were separated via centrifugation and dried at 60∘Cfor 12 h Products were collected and tested using XRD tomeasure their crystal stabilities
3 Results and Discussions
31 XRD and XPS The X-ray diffraction (XRD) patterns ofas-prepared AgAgCl-Bi
2WO6composites and pure Bi
2WO6
and AgAgCl are shown in Figure 1 The diffraction peaks ofpure Bi
2WO6agreed well with the orthorhombic structure
(space group Pbca (61) PDF card number 00-039-0256)[13] Specifically peaks at 2120579 = 283∘ 327∘ 471∘ 558∘and 5854∘ were assigned to the (131) (060)(200)(002)(260)(202) (191)(331)(133) and (262) planes of Bi
2WO6
respectively Samples with deposit amounts of AgAgCl largerthan and including 4wt showed characteristic peaks of Agand AgCl As for the small amount of Ag0 the peak wasweak In Figure 2 the XRD pattern of AgAgCl (10 wt)-Bi2WO6was enlarged and each species in the composite
was identified Excluding peaks from Bi2WO6 peaks at 2120579 =
278∘ (Figure 2(a)) 322∘ 462∘ 548∘ and 575∘ (Figure 2(c))were found indicating the existence of AgCl (cubic structurespace group Fm-3m (225) PDF card number 00-006-0480)Meanwhile the peak at 2120579= 382∘ (Figure 2(b)) was attributedto the (111) crystal plane of Ag (PDF card number 01-087-0719)The lattice parameters of Bi
2WO6are 119886 = 54513 A 119887 =
164192 A and 119888 = 54587 A In regard to these parameters
International Journal of Photoenergy 3
Table 1 Lattice parameters of Bi2WO6and AgAgCl-Bi
2WO6composites
Amount of AgAgCl (wt) 119886 119887 119888
0 (pure Bi2WO6) 54513 (plusmn0) 164192 (plusmn0) 54587 (plusmn0)
1 54381 (minus02) 164363 (+01) 54434 (minus03)2 54274 (minus04) 164413 (+01) 54490 (minus02)4 54378 (minus02) 164205 (+001) 54445 (minus03)8 54381 (minus02) 164392 (+01) 54534 (minus01)10 54399 (minus02) 164473 (+02) 54561 (minus005)20 54361 (minus03) 164432 (+01) 54600 (+002)
30 20 40 50 60 70
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
20 30 40 50 60 70 2120579 (deg)
2120579 (deg)
AgAgCl
(131
)
(060
)(200
)(002
)
(260
)(202
)
(191
)(331
)(133
)
(262
)
(111
)
(111
)
(200
)(200
)
(220
)
(220
)
(311
)
(222
)
(400)
Inte
nsity
(au
)
20wt
10wt
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
8wt
4wt
2wt
1wt
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
Bi2WO6
Bi2WO6AgAgCl-
00-039-0256)Bi2WO6 (PDF
Figure 1 XRD patterns of as-prepared samples pure Bi2WO6
AgAgCl and AgAgCl-Bi2WO6composites
shown in Table 1 negligible differences between them wereobserved This indicates that loading of AgAgCl may notdestroy the main structure of Bi
2WO6and merely laid upon
its surface as opposed to covalently anchoring to its lattice[14]
The elemental compositions and chemical states ofAgAgCl-Bi
2WO6composites were determined by X-ray
photoelectron spectroscopy In Figure 3(a) survey spectraand high-resolution scans of typical orbits in AgAgCl(10 wt)-Bi
2WO6are illustrated Specifically in the survey
spectra all elements of the composite (Bi W O Ag andCl) were demonstrated The spectra were calibrated using C1s the binding energy of which was 2846 eV As for high-resolution XPS spectra in Figure 3(b) two strong peakscentered at 16450 eV and 15919 eV indicate that the valenceof Bi in the composite was +2 [15] Furthermore binding
energies of 3757 eV and 3541 eV for W 4f52
and W 4f72
respectively were found in Figure 3(c) whichwere confirmedW in the composite with valence of +6 [15 16] The largestpeak in Figure 3(d) could be separated into 3 smaller peakswhich are corresponding well with O in the composite withforms of Bi
2WO6at 53028 eV ndashOH at 53128 eV and H
2O at
53196 eV The existence of a negligible fraction of hydroxylanion and H
2O in the composite may be attributed to the
reaction of atmospheric water with the oxide surface andthe chemisorbed water vapor on top of the oxide surface[17] Silver peaks at 37339 eV and 36730 eV in Figure 3(e)were ascribed to binding energies of Ag 3d
32and Ag 3d
52
respectively in the presence of Ag+ in AgCl [18] Smallerpeaks located at 37439 eV and 36832 eV for binding energiesof Ag 3d
32and Ag 3d
52were assigned to that of metallic Ag0
[18] This may suggest that metallic Ag0 can be found in thecomposite
32 SEM EDS and TEM Morphologies of as-prepared sam-ples were measured by SEM and TEM the results of whichare shown in Figure 4 Bi
2WO6synthesized by the hydrother-
mal method described in this work exhibited a nanoplate-built hierarchical flower-like structure (Figure 4(a)) Similarstructures were also reported in the literatures [19 20] Apotential mechanism for the formation of this superstructureis shown in Scheme 1 The scheme shows that an irregularstructure is formed through self-aggregation at the first stepAs for the lowpH (lt1) Bi
2O2
2+ andWO4
2minus ions are generatedin solution and may be nucleated onto protuberances onthe surface of solid spheresThis dissolution-recrystallizationprocess is called Ostwald ripening The plate-like structure isowed to the intrinsic anisotropic growth habits of Bi
2WO6
[21] According to the Gibbs-Thomson law larger particlesgrow at the cost of small particles as for the energy differ-ence in solubility Flower-like superstructures eventually self-organize after sufficient duration of hydrothermal treatmentThe size of each hierarchicalmicrosphere was around 2-3 120583mAgAgCl growing on the surface of Bi
2WO6is shown in
Figure 4(b) Smaller plate-like AgCl could be observed asrandomly loaded on its surface and metallic silver (Ag0) wasnot observed However Ag0 was shown to be present in thecomposite based on TEM imaging results (Figure 4(c)) Inthe inset of Figure 4(c) nanoparticles with a size of no morethan 5 nmcould possibly be identified asmetallic silver (Ag0)Furthermore EDS was performed on the composite and isillustrated in Figure 5 Characteristic peaks of all elements
4 International Journal of Photoenergy
Self-aggregation Ostwald ripening Self-organization
Scheme 1 Potential mechanism of forming the hierarchical flower-like superstructure of Bi2WO6
27 28 29 30 53 54 55 56 57 58378 380 382 384 386 388
30 20 40 50 60 70
AgCl (PDF 00-006-0480)
2120579 (deg)
2120579 (deg) 2120579 (deg) 2120579 (deg)
(a)
(a)
(b)
(b)
(c)
(c)
Inte
nsity
(au
)
00-039-0256)Bi2WO6 (PDFAg (PDF 01-087-0719) AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Figure 2 XRD pattern of AgAgCl (10wt)-Bi2WO6
in the composite were found which further confirms thesuccessful synthesis of AgAgCl-Bi
2WO6in this work
33 UV-Vis Diffused Reflectance Spectra (DRS) The opticalabsorbent properties of the AgAgCl-Bi
2WO6composite
were measured using UV-Vis diffused reflectance spec-troscopy Spectra of pure Bi
2WO6 AgAgCl and AgAgCl
(10 wt)-Bi2WO6are illustrated in Figure 6(a) After loading
AgAgCl onto Bi2WO6 the absorbent ability of the photocat-
alyst in the visible-light range was enhanced This is mainlydue to the plasmon resonance of photoreduced silver (Ag0)fromAgCl [2] which could also be evidence for the existenceof Ag0 in the composite To further explore the band gap (119864
119892)
of samples the classical Tauc equation (1) was employed asfollows
120572119864photon = 119870 (119864photon minus 119864119892)1198992
119864photon = ℎ](1)
where 120572 ℎ ] and 119870 are the absorption coefficient thePlanck constant the irradiation frequency and the constantfor semiconductors (usually equal to 1) respectively Theconstant 119899 depends on the type of band gap where 119899 = 1is for direct transition and 119899 = 4 is for indirect transitionThe band gap of the as-prepared Bi
2WO6in this work is
characteristic of a direct transition (Figure 7) so 119899 is equal
International Journal of Photoenergy 5
O 1s
Ag 3dC 1s
Cl 2p W 4f
Bi 4fIn
tens
ity (a
u)
02004006008001000
Binding energy (eV)
(a)
15919 eV
16450 eV
Bi 4f72
Bi 4f52
Bi 4f
Inte
nsity
(au
)
168 166 164 162 160 158 156 154170
Binding energy (eV)
(b)
3757 eV W 4f52
3541 eVW 4f72
W 4f
Inte
nsity
(au
)
38 36 34 3240
Binding energy (eV)
(c)
O 1s53028 eV
O 1s (W-O amp Bi-O)
O 1s (minusOH)53128 eV
O 1s (H2O)53196 eV
Inte
nsity
(au
)
528530532534
Binding energy (eV)
(d)
Ag 3d
3d52
3d32
36730 eV
37339 eV
37439 eV 36832 eV
Inte
nsity
(au
)
376 374 372 370 368 366 364378
Binding energy (eV)
(e)
19946 eV Cl 2p12
Cl 2p32Cl 2p
19783 eV
Inte
nsity
(au
)
200202 196198
Binding energy (eV)
(f)
Figure 3 XPS spectra of AgAgCl (10wt)-Bi2WO6composite (a) survey spectra and high-resolution orbits scan of (b) Bi 4f (c) W 4f (d)
O 1s (e) Ag 3d and (f) Cl 2p
6 International Journal of Photoenergy
1120583m
(a)
1120583m
(b)
Ag010nm
20nm
AgAgCl
Bi2WO6
(c)
Figure 4 SEM images of pure Bi2WO6(a) and AgAgCl (10wt)-Bi
2WO6composite (b) and TEM images of AgAgCl (10wt)-Bi
2WO6
composite (c)
Cl
ClCl
C
O
W
W
Bi Bi
Inte
nsity
(au
)
AgAg
1 2 3 4 50
Energy (keV)
Figure 5 EDS of AgAgCl (10wt)-Bi2WO6composite
to 4 By plotting (120572119864photon)12 versus 119864photon as illustrated
in Figure 6(b) the intercept at the horizontal axis is theband gap value This indicates that AgAgCl in compositesnarrowed the band gap from 270 eV to 257 eV comparedto pure Bi
2WO6 which could widen the edge wavelength
of incidence from 4593 nm to 4825 nm This indicates that
AgAgCl-Bi2WO6composites could be effectively activated
under visible-light irradiation
34 Photocatalytic Activity Test under Visible Light Photo-catalytic activities of as-prepared samples were tested bydegrading RhB (10mgL) All of the screening test resultsare plotted in Figure 8 The removal efficiencies for pureBi2WO6and AgAgCl were 388 and 653 in 45min
respectively By increasing the loading amount of AgAgCl inthe composites from 1wt to 10wt removal efficiencies ofthe composites were increased up to 100 after 45min undervisible light This enhancement effect may be attributed tothe establishment of a heterojunction between AgAgCl andBi2WO6[3 14 23] However further increasing the amount
of AgAgCl in the composites deteriorates the photocatalyticdegradation performances This may be interpreted as largernanoparticles which are loaded onto Bi
2WO6possibly weak-
ening the anchoring forces between them and destroying theheterostructure
Langmuir-Hinshelwood kinetic analysis was applied toRhB degradation in the presence of as-prepared photocata-lysts Trials performed with diluted concentrations of RhB(119888119900lt 10minus3molL) showed that the Langmuir-Hinshelwood
International Journal of Photoenergy 7
Bi2WO6
Bi2WO6AgAgCl-AgAgCl
Abso
rban
ce (a
u)
500400 600300 550350 450
Wavelength (nm)
(a)
Bi2WO6
Bi2WO6AgAgCl-
(120572timesE
phot
on)12
30 35 402520
Ephoton (eV)
(b)
Figure 6 (a) UV-Vis diffused reflectance spectra and (b) (120572119864photon)12-119864photon curves of as-prepared pure Bi
2WO6 AgAgCl and AgAgCl
(10wt)-Bi2WO6
G Z T Y S X U Rminus10
minus5
0
5
Band
ener
gy (e
V)
Figure 7 Band gap of Bi2WO6(simulated by Quantum Espresso
[22])
model could be simplified to a pseudo-first-order reactionmodel [24] expressed as follows
ln(119888119900
119888) = 119896119903times 119870 times 119905 = 119896
1015840119905 (2)
where 119905 119888119900 and 119888 are the time the initial concentration and
concentration at each specific reaction time 119905 of RhB 119896119903is
the reaction rate constant 119870 is the adsorption coefficient ofthe pollutant on the photocatalyst and 1198961015840 is pseudo-first-order reaction kinetics constant used as the parameter toevaluate the performances of as-prepared photocatalysts indegrading pollutants A plot of ln(119888
119900119888) as a function 119905 is
found in Figure 9 where the slope of the line of best fit is
1wt2wt4wt8wt
10wt20wtBi2WO6AgAgCl
39363330 42 4521 24 271512963 180
Time (min)
00
01
02
03
04
05
06
07
08
09
10
cc o
Figure 8 Photocatalytic degradation of RhB (10mgL) undervisible light with as-prepared pure Bi
2WO6 AgAgCl andAgAgCl-
Bi2WO6composites
the pseudo-first-order kinetics constant the results of whichare summarized in Table 2 The excellent linearity of eachline of best fit indicates that the photocatalytic degradationof RhB under visible-light irradiation in the presence ofAgAgCl-Bi
2WO6follows first-order kinetics The process
carried out with pure Bi2WO6as the photocatalyst exhibited
8 International Journal of Photoenergy
Table 2 Pseudo-first-order reaction rate constants for various processes
Bi2WO6
1 wt 2wt 4wt 8wt 10wt 20wt AgAgClPseudo-first-order119896 (10minus2minminus1) 1047 2733 3371 3930 4576 5688 4508 20371198772 09999 09961 09989 09979 09989 09993 09987 09939
Bi2WO6
1wt2wt4wt
8wt10wt20wtAgAgCl
3 6 90 18 2112 15
Time (min)
00
02
04
06
08
10
12
14
c oc
)ln
(
Figure 9 Photocatalytic kinetics of each process
the lowest reaction constant while loading of AgAgCl ontoBi2WO6increased the constant up to 54 times compared
to that of pure Bi2WO6at 10 wt AgAgCl These results
confirm that the presence of AgAgCl in the compositessignificantly increases photocatalytic activity with regard tothe degradation of organic pollutants
The stepwise mechanism for the degradation of RhB wasobserved by taking UV-Vis spectra which are illustrated inFigure 10 In the inset table the positions of characteristicpeaks for each intermediate species are summarized [25] Itcan be concluded that twoprocesses of RhBdegradation existnamely deethylation and destruction of the aromatic ring Inthe deethylation process RhB is decomposed into NNN1015840-Triethyl-Rhodamine (TER) NN1015840-Diethyl-Rhodamine(DER) N-Ethyl-Rhodamine (MER) and Rhodamine theUV-Vis characteristic peaks of which are located at wave-lengths of 539 nm 522 nm 510 nm and 498 nm respectivelyIn the first 33min peak positions blue-shifted from 554 nmto 498 nm indicating that RhB degraded into RhodamineAfter that peak positions stabilized at 498 nm and graduallyreduced in intensity This may be attributed to the degrada-tion of Rhodamine into smaller species such asH
2OandCO
2
The photocatalytic activity with respect to the degra-dation of the colourless organic compound phenol wasinvestigated and is illustrated in Figure 11 These resultsaimed to confirm the increased photocatalytic activity in the
0min3min6min9min12min15min18min21min
24min27min30min33min36min39min42min45min
Dye 120582max (nm)
00
02
04
06
08
10
12
14
16
Abso
rban
ce (a
u)
600400 500 700300 450 650350 550
Wavelength (nm)
Rhodamine B
Rhodamine
NNN998400-Triethyl-Rhodamine (TER)
NN998400-Diethyl-Rhodamine (DER)N-Ethyl-Rhodamine (MER)
554
539
522
510
498
Figure 10 UV-Vis spectra of solutions taken during the photocat-alytic process in the presence of AgAgCl (10wt)-Bi
2WO6(inset
table shows characteristic wavelength for each intermediate speciesin water [25])
presence of the AgAgCl-Bi2WO6composite under visible
light attributed to the surface plasmon resonance effectinstead of photosensitization of the dye (RhB in this work)[26] The composite performed well in the degradation ofphenol (approximately 30 of phenol was converted in45min) which was a better performance than that exhibitedby pure Bi
2WO6(only about 5 of phenol was converted
in 45min) This confirmed that the enhancement effect ofloading AgAgCl onto Bi
2WO6exists under visible-light
irradiation
35 Roles of Radical Species Holes (h+) and free radicalsespecially ∙OH are regarded as the main oxidative species inphotocatalytic degradation of organic pollutants [27] In thisstudy EDTA-2Na and 2-Butanol were chosen as the hole andhydroxyl radical scavengers respectively [28] When holeswere quenched only 15 of RhB was removed (Figure 12)Comparatively there was little influence when 2-Butanolwas added to quench hydroxyl radicals This suggests thatthe hydroxyl radical is not the main oxidative species in
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
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Analytical ChemistryInternational Journal of
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Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
2 International Journal of Photoenergy
Apossiblemechanismof the photocatalytic oxidation processin the presence of the AgAgCl-Bi
2WO6composite was also
explored and proposedThe enhanced photocatalytic activitymay be regarded as solid evidence of the potential applicationof AgAgCl in photocatalytic oxidation processes
2 Experimental
21 Preparation of Bi2WO6and AgAgCl-Bi
2WO6Compos-
ites All of the reagents were purchased from the Sigma-Aldrich Company were of analytical purities and wereused as received Bi
2WO6was synthesized by a hydrother-
mal method In a typical process 09702 g Bi(NO3)3sdot5H2O
were dissolved in 20mL acetic acid termed solution Awhich was magnetically stirred for 10min Next 03298 gNa2WO4sdot2H2O were dissolved in 40mL distilled deionized
water (DDW) termed solution B Solution B was addeddropwise into solution A and stirredmagnetically for 30minThe suspension was then transferred to a 100mL Teflon-linedstainless steel autoclave (approximately 60 of its maximumvolume) and heated at 180∘C for 20 h After the autoclavewas allowed to cool to room temperature the precipitate wasseparated by centrifugation and washed once with ethanoland then twice with DDW The precipitate was then dried at60∘C for 12 h
The AgAgCl-Bi2WO6composite was prepared by the
photoreduction method Typically 032 g Bi2WO6were dis-
persed in 40mL DDW and sonicated for 30min Next 024 gNaCl (excess amount) was added to the suspension whichwas termed solution C Meanwhile 00421 g AgNO
3were
added to 20mL DDW termed solution D Solution D wasadded dropwise to solution C with vigorous stirring for30min Products were separated by centrifugation and dis-persed in 40mL DDW and then illuminated under a 300Whalogen tungsten projector lamp (Ushio) for 30min Finalproducts were separated via centrifugation washed twicewith DDW and dried at 60∘C for 12 h The sample was thencollected and labelled as AgAgCl (10 wt)-Bi
2WO6 Simi-
larly AgAgCl (1 wt)-Bi2WO6 AgAgCl (2 wt)-Bi
2WO6
AgAgCl (4wt)-Bi2WO6 AgAgCl (8 wt)-Bi
2WO6 and
AgAgCl (20wt)-Bi2WO6were also prepared
22 Characterization X-ray diffraction (XRD) analysis wasperformed using a Rigaku Ultima IV Diffractometer withCuK120572 radiation (120582 = 015418 nm) at 40 kV and 44mASurface elements and the chemical states of samples weretested using a XSAM-800 X-ray Photoelectron Spectroscope(XPS) A field-emission scanning electron microscope (FE-SEM JEOL JSM-7500F) using energy dispersive X-ray spec-troscopy (EDS) and transmission electronmicroscopy (TEMJEM-2100F) were applied to explore the morphologies ofsamples Acceleration voltages of the SEM and TEM were300 kV and 200 kV respectively The Thermo Evolution300 spectrophotometer was used to evaluate the ultraviolet-visible (UV-Vis) diffuse reflectance spectra (DRS) of thephotocatalysts
23 Photocatalytic Activity Test The target organic pol-lutant was Rhodamine B (RhB) The characteristic peak
in UV-Vis spectroscopy of RhB is found at a wavelengthof 554 nm which was used to calculate its concentrationbased on the Beer-Lambert law A 500mL beaker with acooling jacket maintaining the system at 20∘C served asthe photocatalytic reactor The visible-light source was a300W halogen tungsten projector lamp (Ushio) with a cut-off (Kenko Zeta transmittancegt 90) to filter out irradiationwith a wavelength below 400 nm The distance between theirradiation source and the top of the beaker was 10 cm andthe irradiation intensity was measured by a quantum meter(Biospherical QSL-2100 400 nm lt 120582 lt 700 nm) to be 11 times10minus2 Einsteinsmminus2 sminus1 In each batch 100mL fresh solutionwith a concentration of RhB at 10mgL (10 ppm) was addedto the reactor and mixed with as-prepared photocatalysts inthe absence of light for 30min to ensure that adsorption-desorption equilibrium was achieved The quantity of photo-catalyst added was 05 gL After mixing the light was turnedon to begin the photocatalytic process An aliquot of 1mLsuspension was taken every 3min for 45min and tested usingaGenysys 10-UV spectrophotometer (Geneq Inc) To explorethe roles of radical species EDTA-2Na and 2-Butanol withconcentrations of 001molL were added to the reactor
To study the degradation of phenol 100mL phenol solu-tion with a concentration of 10mgL (ppm) was mixed withan AgAgCl-Bi
2WO6composite Samples taken during the
photocatalytic processwere tested usingUV-Vis spectroscopywith the peak absorption at a wavelength of 270 nm Otherprocedures used the same process as that of the degradationof RhB
To recycle the photocatalysts photocatalysts were sepa-rated by centrifugation between experiments and then usedin the following experiment without a wash The final usedproducts were separated via centrifugation and dried at 60∘Cfor 12 h Products were collected and tested using XRD tomeasure their crystal stabilities
3 Results and Discussions
31 XRD and XPS The X-ray diffraction (XRD) patterns ofas-prepared AgAgCl-Bi
2WO6composites and pure Bi
2WO6
and AgAgCl are shown in Figure 1 The diffraction peaks ofpure Bi
2WO6agreed well with the orthorhombic structure
(space group Pbca (61) PDF card number 00-039-0256)[13] Specifically peaks at 2120579 = 283∘ 327∘ 471∘ 558∘and 5854∘ were assigned to the (131) (060)(200)(002)(260)(202) (191)(331)(133) and (262) planes of Bi
2WO6
respectively Samples with deposit amounts of AgAgCl largerthan and including 4wt showed characteristic peaks of Agand AgCl As for the small amount of Ag0 the peak wasweak In Figure 2 the XRD pattern of AgAgCl (10 wt)-Bi2WO6was enlarged and each species in the composite
was identified Excluding peaks from Bi2WO6 peaks at 2120579 =
278∘ (Figure 2(a)) 322∘ 462∘ 548∘ and 575∘ (Figure 2(c))were found indicating the existence of AgCl (cubic structurespace group Fm-3m (225) PDF card number 00-006-0480)Meanwhile the peak at 2120579= 382∘ (Figure 2(b)) was attributedto the (111) crystal plane of Ag (PDF card number 01-087-0719)The lattice parameters of Bi
2WO6are 119886 = 54513 A 119887 =
164192 A and 119888 = 54587 A In regard to these parameters
International Journal of Photoenergy 3
Table 1 Lattice parameters of Bi2WO6and AgAgCl-Bi
2WO6composites
Amount of AgAgCl (wt) 119886 119887 119888
0 (pure Bi2WO6) 54513 (plusmn0) 164192 (plusmn0) 54587 (plusmn0)
1 54381 (minus02) 164363 (+01) 54434 (minus03)2 54274 (minus04) 164413 (+01) 54490 (minus02)4 54378 (minus02) 164205 (+001) 54445 (minus03)8 54381 (minus02) 164392 (+01) 54534 (minus01)10 54399 (minus02) 164473 (+02) 54561 (minus005)20 54361 (minus03) 164432 (+01) 54600 (+002)
30 20 40 50 60 70
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
20 30 40 50 60 70 2120579 (deg)
2120579 (deg)
AgAgCl
(131
)
(060
)(200
)(002
)
(260
)(202
)
(191
)(331
)(133
)
(262
)
(111
)
(111
)
(200
)(200
)
(220
)
(220
)
(311
)
(222
)
(400)
Inte
nsity
(au
)
20wt
10wt
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
8wt
4wt
2wt
1wt
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
Bi2WO6
Bi2WO6AgAgCl-
00-039-0256)Bi2WO6 (PDF
Figure 1 XRD patterns of as-prepared samples pure Bi2WO6
AgAgCl and AgAgCl-Bi2WO6composites
shown in Table 1 negligible differences between them wereobserved This indicates that loading of AgAgCl may notdestroy the main structure of Bi
2WO6and merely laid upon
its surface as opposed to covalently anchoring to its lattice[14]
The elemental compositions and chemical states ofAgAgCl-Bi
2WO6composites were determined by X-ray
photoelectron spectroscopy In Figure 3(a) survey spectraand high-resolution scans of typical orbits in AgAgCl(10 wt)-Bi
2WO6are illustrated Specifically in the survey
spectra all elements of the composite (Bi W O Ag andCl) were demonstrated The spectra were calibrated using C1s the binding energy of which was 2846 eV As for high-resolution XPS spectra in Figure 3(b) two strong peakscentered at 16450 eV and 15919 eV indicate that the valenceof Bi in the composite was +2 [15] Furthermore binding
energies of 3757 eV and 3541 eV for W 4f52
and W 4f72
respectively were found in Figure 3(c) whichwere confirmedW in the composite with valence of +6 [15 16] The largestpeak in Figure 3(d) could be separated into 3 smaller peakswhich are corresponding well with O in the composite withforms of Bi
2WO6at 53028 eV ndashOH at 53128 eV and H
2O at
53196 eV The existence of a negligible fraction of hydroxylanion and H
2O in the composite may be attributed to the
reaction of atmospheric water with the oxide surface andthe chemisorbed water vapor on top of the oxide surface[17] Silver peaks at 37339 eV and 36730 eV in Figure 3(e)were ascribed to binding energies of Ag 3d
32and Ag 3d
52
respectively in the presence of Ag+ in AgCl [18] Smallerpeaks located at 37439 eV and 36832 eV for binding energiesof Ag 3d
32and Ag 3d
52were assigned to that of metallic Ag0
[18] This may suggest that metallic Ag0 can be found in thecomposite
32 SEM EDS and TEM Morphologies of as-prepared sam-ples were measured by SEM and TEM the results of whichare shown in Figure 4 Bi
2WO6synthesized by the hydrother-
mal method described in this work exhibited a nanoplate-built hierarchical flower-like structure (Figure 4(a)) Similarstructures were also reported in the literatures [19 20] Apotential mechanism for the formation of this superstructureis shown in Scheme 1 The scheme shows that an irregularstructure is formed through self-aggregation at the first stepAs for the lowpH (lt1) Bi
2O2
2+ andWO4
2minus ions are generatedin solution and may be nucleated onto protuberances onthe surface of solid spheresThis dissolution-recrystallizationprocess is called Ostwald ripening The plate-like structure isowed to the intrinsic anisotropic growth habits of Bi
2WO6
[21] According to the Gibbs-Thomson law larger particlesgrow at the cost of small particles as for the energy differ-ence in solubility Flower-like superstructures eventually self-organize after sufficient duration of hydrothermal treatmentThe size of each hierarchicalmicrosphere was around 2-3 120583mAgAgCl growing on the surface of Bi
2WO6is shown in
Figure 4(b) Smaller plate-like AgCl could be observed asrandomly loaded on its surface and metallic silver (Ag0) wasnot observed However Ag0 was shown to be present in thecomposite based on TEM imaging results (Figure 4(c)) Inthe inset of Figure 4(c) nanoparticles with a size of no morethan 5 nmcould possibly be identified asmetallic silver (Ag0)Furthermore EDS was performed on the composite and isillustrated in Figure 5 Characteristic peaks of all elements
4 International Journal of Photoenergy
Self-aggregation Ostwald ripening Self-organization
Scheme 1 Potential mechanism of forming the hierarchical flower-like superstructure of Bi2WO6
27 28 29 30 53 54 55 56 57 58378 380 382 384 386 388
30 20 40 50 60 70
AgCl (PDF 00-006-0480)
2120579 (deg)
2120579 (deg) 2120579 (deg) 2120579 (deg)
(a)
(a)
(b)
(b)
(c)
(c)
Inte
nsity
(au
)
00-039-0256)Bi2WO6 (PDFAg (PDF 01-087-0719) AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Figure 2 XRD pattern of AgAgCl (10wt)-Bi2WO6
in the composite were found which further confirms thesuccessful synthesis of AgAgCl-Bi
2WO6in this work
33 UV-Vis Diffused Reflectance Spectra (DRS) The opticalabsorbent properties of the AgAgCl-Bi
2WO6composite
were measured using UV-Vis diffused reflectance spec-troscopy Spectra of pure Bi
2WO6 AgAgCl and AgAgCl
(10 wt)-Bi2WO6are illustrated in Figure 6(a) After loading
AgAgCl onto Bi2WO6 the absorbent ability of the photocat-
alyst in the visible-light range was enhanced This is mainlydue to the plasmon resonance of photoreduced silver (Ag0)fromAgCl [2] which could also be evidence for the existenceof Ag0 in the composite To further explore the band gap (119864
119892)
of samples the classical Tauc equation (1) was employed asfollows
120572119864photon = 119870 (119864photon minus 119864119892)1198992
119864photon = ℎ](1)
where 120572 ℎ ] and 119870 are the absorption coefficient thePlanck constant the irradiation frequency and the constantfor semiconductors (usually equal to 1) respectively Theconstant 119899 depends on the type of band gap where 119899 = 1is for direct transition and 119899 = 4 is for indirect transitionThe band gap of the as-prepared Bi
2WO6in this work is
characteristic of a direct transition (Figure 7) so 119899 is equal
International Journal of Photoenergy 5
O 1s
Ag 3dC 1s
Cl 2p W 4f
Bi 4fIn
tens
ity (a
u)
02004006008001000
Binding energy (eV)
(a)
15919 eV
16450 eV
Bi 4f72
Bi 4f52
Bi 4f
Inte
nsity
(au
)
168 166 164 162 160 158 156 154170
Binding energy (eV)
(b)
3757 eV W 4f52
3541 eVW 4f72
W 4f
Inte
nsity
(au
)
38 36 34 3240
Binding energy (eV)
(c)
O 1s53028 eV
O 1s (W-O amp Bi-O)
O 1s (minusOH)53128 eV
O 1s (H2O)53196 eV
Inte
nsity
(au
)
528530532534
Binding energy (eV)
(d)
Ag 3d
3d52
3d32
36730 eV
37339 eV
37439 eV 36832 eV
Inte
nsity
(au
)
376 374 372 370 368 366 364378
Binding energy (eV)
(e)
19946 eV Cl 2p12
Cl 2p32Cl 2p
19783 eV
Inte
nsity
(au
)
200202 196198
Binding energy (eV)
(f)
Figure 3 XPS spectra of AgAgCl (10wt)-Bi2WO6composite (a) survey spectra and high-resolution orbits scan of (b) Bi 4f (c) W 4f (d)
O 1s (e) Ag 3d and (f) Cl 2p
6 International Journal of Photoenergy
1120583m
(a)
1120583m
(b)
Ag010nm
20nm
AgAgCl
Bi2WO6
(c)
Figure 4 SEM images of pure Bi2WO6(a) and AgAgCl (10wt)-Bi
2WO6composite (b) and TEM images of AgAgCl (10wt)-Bi
2WO6
composite (c)
Cl
ClCl
C
O
W
W
Bi Bi
Inte
nsity
(au
)
AgAg
1 2 3 4 50
Energy (keV)
Figure 5 EDS of AgAgCl (10wt)-Bi2WO6composite
to 4 By plotting (120572119864photon)12 versus 119864photon as illustrated
in Figure 6(b) the intercept at the horizontal axis is theband gap value This indicates that AgAgCl in compositesnarrowed the band gap from 270 eV to 257 eV comparedto pure Bi
2WO6 which could widen the edge wavelength
of incidence from 4593 nm to 4825 nm This indicates that
AgAgCl-Bi2WO6composites could be effectively activated
under visible-light irradiation
34 Photocatalytic Activity Test under Visible Light Photo-catalytic activities of as-prepared samples were tested bydegrading RhB (10mgL) All of the screening test resultsare plotted in Figure 8 The removal efficiencies for pureBi2WO6and AgAgCl were 388 and 653 in 45min
respectively By increasing the loading amount of AgAgCl inthe composites from 1wt to 10wt removal efficiencies ofthe composites were increased up to 100 after 45min undervisible light This enhancement effect may be attributed tothe establishment of a heterojunction between AgAgCl andBi2WO6[3 14 23] However further increasing the amount
of AgAgCl in the composites deteriorates the photocatalyticdegradation performances This may be interpreted as largernanoparticles which are loaded onto Bi
2WO6possibly weak-
ening the anchoring forces between them and destroying theheterostructure
Langmuir-Hinshelwood kinetic analysis was applied toRhB degradation in the presence of as-prepared photocata-lysts Trials performed with diluted concentrations of RhB(119888119900lt 10minus3molL) showed that the Langmuir-Hinshelwood
International Journal of Photoenergy 7
Bi2WO6
Bi2WO6AgAgCl-AgAgCl
Abso
rban
ce (a
u)
500400 600300 550350 450
Wavelength (nm)
(a)
Bi2WO6
Bi2WO6AgAgCl-
(120572timesE
phot
on)12
30 35 402520
Ephoton (eV)
(b)
Figure 6 (a) UV-Vis diffused reflectance spectra and (b) (120572119864photon)12-119864photon curves of as-prepared pure Bi
2WO6 AgAgCl and AgAgCl
(10wt)-Bi2WO6
G Z T Y S X U Rminus10
minus5
0
5
Band
ener
gy (e
V)
Figure 7 Band gap of Bi2WO6(simulated by Quantum Espresso
[22])
model could be simplified to a pseudo-first-order reactionmodel [24] expressed as follows
ln(119888119900
119888) = 119896119903times 119870 times 119905 = 119896
1015840119905 (2)
where 119905 119888119900 and 119888 are the time the initial concentration and
concentration at each specific reaction time 119905 of RhB 119896119903is
the reaction rate constant 119870 is the adsorption coefficient ofthe pollutant on the photocatalyst and 1198961015840 is pseudo-first-order reaction kinetics constant used as the parameter toevaluate the performances of as-prepared photocatalysts indegrading pollutants A plot of ln(119888
119900119888) as a function 119905 is
found in Figure 9 where the slope of the line of best fit is
1wt2wt4wt8wt
10wt20wtBi2WO6AgAgCl
39363330 42 4521 24 271512963 180
Time (min)
00
01
02
03
04
05
06
07
08
09
10
cc o
Figure 8 Photocatalytic degradation of RhB (10mgL) undervisible light with as-prepared pure Bi
2WO6 AgAgCl andAgAgCl-
Bi2WO6composites
the pseudo-first-order kinetics constant the results of whichare summarized in Table 2 The excellent linearity of eachline of best fit indicates that the photocatalytic degradationof RhB under visible-light irradiation in the presence ofAgAgCl-Bi
2WO6follows first-order kinetics The process
carried out with pure Bi2WO6as the photocatalyst exhibited
8 International Journal of Photoenergy
Table 2 Pseudo-first-order reaction rate constants for various processes
Bi2WO6
1 wt 2wt 4wt 8wt 10wt 20wt AgAgClPseudo-first-order119896 (10minus2minminus1) 1047 2733 3371 3930 4576 5688 4508 20371198772 09999 09961 09989 09979 09989 09993 09987 09939
Bi2WO6
1wt2wt4wt
8wt10wt20wtAgAgCl
3 6 90 18 2112 15
Time (min)
00
02
04
06
08
10
12
14
c oc
)ln
(
Figure 9 Photocatalytic kinetics of each process
the lowest reaction constant while loading of AgAgCl ontoBi2WO6increased the constant up to 54 times compared
to that of pure Bi2WO6at 10 wt AgAgCl These results
confirm that the presence of AgAgCl in the compositessignificantly increases photocatalytic activity with regard tothe degradation of organic pollutants
The stepwise mechanism for the degradation of RhB wasobserved by taking UV-Vis spectra which are illustrated inFigure 10 In the inset table the positions of characteristicpeaks for each intermediate species are summarized [25] Itcan be concluded that twoprocesses of RhBdegradation existnamely deethylation and destruction of the aromatic ring Inthe deethylation process RhB is decomposed into NNN1015840-Triethyl-Rhodamine (TER) NN1015840-Diethyl-Rhodamine(DER) N-Ethyl-Rhodamine (MER) and Rhodamine theUV-Vis characteristic peaks of which are located at wave-lengths of 539 nm 522 nm 510 nm and 498 nm respectivelyIn the first 33min peak positions blue-shifted from 554 nmto 498 nm indicating that RhB degraded into RhodamineAfter that peak positions stabilized at 498 nm and graduallyreduced in intensity This may be attributed to the degrada-tion of Rhodamine into smaller species such asH
2OandCO
2
The photocatalytic activity with respect to the degra-dation of the colourless organic compound phenol wasinvestigated and is illustrated in Figure 11 These resultsaimed to confirm the increased photocatalytic activity in the
0min3min6min9min12min15min18min21min
24min27min30min33min36min39min42min45min
Dye 120582max (nm)
00
02
04
06
08
10
12
14
16
Abso
rban
ce (a
u)
600400 500 700300 450 650350 550
Wavelength (nm)
Rhodamine B
Rhodamine
NNN998400-Triethyl-Rhodamine (TER)
NN998400-Diethyl-Rhodamine (DER)N-Ethyl-Rhodamine (MER)
554
539
522
510
498
Figure 10 UV-Vis spectra of solutions taken during the photocat-alytic process in the presence of AgAgCl (10wt)-Bi
2WO6(inset
table shows characteristic wavelength for each intermediate speciesin water [25])
presence of the AgAgCl-Bi2WO6composite under visible
light attributed to the surface plasmon resonance effectinstead of photosensitization of the dye (RhB in this work)[26] The composite performed well in the degradation ofphenol (approximately 30 of phenol was converted in45min) which was a better performance than that exhibitedby pure Bi
2WO6(only about 5 of phenol was converted
in 45min) This confirmed that the enhancement effect ofloading AgAgCl onto Bi
2WO6exists under visible-light
irradiation
35 Roles of Radical Species Holes (h+) and free radicalsespecially ∙OH are regarded as the main oxidative species inphotocatalytic degradation of organic pollutants [27] In thisstudy EDTA-2Na and 2-Butanol were chosen as the hole andhydroxyl radical scavengers respectively [28] When holeswere quenched only 15 of RhB was removed (Figure 12)Comparatively there was little influence when 2-Butanolwas added to quench hydroxyl radicals This suggests thatthe hydroxyl radical is not the main oxidative species in
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 3
Table 1 Lattice parameters of Bi2WO6and AgAgCl-Bi
2WO6composites
Amount of AgAgCl (wt) 119886 119887 119888
0 (pure Bi2WO6) 54513 (plusmn0) 164192 (plusmn0) 54587 (plusmn0)
1 54381 (minus02) 164363 (+01) 54434 (minus03)2 54274 (minus04) 164413 (+01) 54490 (minus02)4 54378 (minus02) 164205 (+001) 54445 (minus03)8 54381 (minus02) 164392 (+01) 54534 (minus01)10 54399 (minus02) 164473 (+02) 54561 (minus005)20 54361 (minus03) 164432 (+01) 54600 (+002)
30 20 40 50 60 70
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
20 30 40 50 60 70 2120579 (deg)
2120579 (deg)
AgAgCl
(131
)
(060
)(200
)(002
)
(260
)(202
)
(191
)(331
)(133
)
(262
)
(111
)
(111
)
(200
)(200
)
(220
)
(220
)
(311
)
(222
)
(400)
Inte
nsity
(au
)
20wt
10wt
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
8wt
4wt
2wt
1wt
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
Bi2WO6AgAgCl-
Bi2WO6
Bi2WO6AgAgCl-
00-039-0256)Bi2WO6 (PDF
Figure 1 XRD patterns of as-prepared samples pure Bi2WO6
AgAgCl and AgAgCl-Bi2WO6composites
shown in Table 1 negligible differences between them wereobserved This indicates that loading of AgAgCl may notdestroy the main structure of Bi
2WO6and merely laid upon
its surface as opposed to covalently anchoring to its lattice[14]
The elemental compositions and chemical states ofAgAgCl-Bi
2WO6composites were determined by X-ray
photoelectron spectroscopy In Figure 3(a) survey spectraand high-resolution scans of typical orbits in AgAgCl(10 wt)-Bi
2WO6are illustrated Specifically in the survey
spectra all elements of the composite (Bi W O Ag andCl) were demonstrated The spectra were calibrated using C1s the binding energy of which was 2846 eV As for high-resolution XPS spectra in Figure 3(b) two strong peakscentered at 16450 eV and 15919 eV indicate that the valenceof Bi in the composite was +2 [15] Furthermore binding
energies of 3757 eV and 3541 eV for W 4f52
and W 4f72
respectively were found in Figure 3(c) whichwere confirmedW in the composite with valence of +6 [15 16] The largestpeak in Figure 3(d) could be separated into 3 smaller peakswhich are corresponding well with O in the composite withforms of Bi
2WO6at 53028 eV ndashOH at 53128 eV and H
2O at
53196 eV The existence of a negligible fraction of hydroxylanion and H
2O in the composite may be attributed to the
reaction of atmospheric water with the oxide surface andthe chemisorbed water vapor on top of the oxide surface[17] Silver peaks at 37339 eV and 36730 eV in Figure 3(e)were ascribed to binding energies of Ag 3d
32and Ag 3d
52
respectively in the presence of Ag+ in AgCl [18] Smallerpeaks located at 37439 eV and 36832 eV for binding energiesof Ag 3d
32and Ag 3d
52were assigned to that of metallic Ag0
[18] This may suggest that metallic Ag0 can be found in thecomposite
32 SEM EDS and TEM Morphologies of as-prepared sam-ples were measured by SEM and TEM the results of whichare shown in Figure 4 Bi
2WO6synthesized by the hydrother-
mal method described in this work exhibited a nanoplate-built hierarchical flower-like structure (Figure 4(a)) Similarstructures were also reported in the literatures [19 20] Apotential mechanism for the formation of this superstructureis shown in Scheme 1 The scheme shows that an irregularstructure is formed through self-aggregation at the first stepAs for the lowpH (lt1) Bi
2O2
2+ andWO4
2minus ions are generatedin solution and may be nucleated onto protuberances onthe surface of solid spheresThis dissolution-recrystallizationprocess is called Ostwald ripening The plate-like structure isowed to the intrinsic anisotropic growth habits of Bi
2WO6
[21] According to the Gibbs-Thomson law larger particlesgrow at the cost of small particles as for the energy differ-ence in solubility Flower-like superstructures eventually self-organize after sufficient duration of hydrothermal treatmentThe size of each hierarchicalmicrosphere was around 2-3 120583mAgAgCl growing on the surface of Bi
2WO6is shown in
Figure 4(b) Smaller plate-like AgCl could be observed asrandomly loaded on its surface and metallic silver (Ag0) wasnot observed However Ag0 was shown to be present in thecomposite based on TEM imaging results (Figure 4(c)) Inthe inset of Figure 4(c) nanoparticles with a size of no morethan 5 nmcould possibly be identified asmetallic silver (Ag0)Furthermore EDS was performed on the composite and isillustrated in Figure 5 Characteristic peaks of all elements
4 International Journal of Photoenergy
Self-aggregation Ostwald ripening Self-organization
Scheme 1 Potential mechanism of forming the hierarchical flower-like superstructure of Bi2WO6
27 28 29 30 53 54 55 56 57 58378 380 382 384 386 388
30 20 40 50 60 70
AgCl (PDF 00-006-0480)
2120579 (deg)
2120579 (deg) 2120579 (deg) 2120579 (deg)
(a)
(a)
(b)
(b)
(c)
(c)
Inte
nsity
(au
)
00-039-0256)Bi2WO6 (PDFAg (PDF 01-087-0719) AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Figure 2 XRD pattern of AgAgCl (10wt)-Bi2WO6
in the composite were found which further confirms thesuccessful synthesis of AgAgCl-Bi
2WO6in this work
33 UV-Vis Diffused Reflectance Spectra (DRS) The opticalabsorbent properties of the AgAgCl-Bi
2WO6composite
were measured using UV-Vis diffused reflectance spec-troscopy Spectra of pure Bi
2WO6 AgAgCl and AgAgCl
(10 wt)-Bi2WO6are illustrated in Figure 6(a) After loading
AgAgCl onto Bi2WO6 the absorbent ability of the photocat-
alyst in the visible-light range was enhanced This is mainlydue to the plasmon resonance of photoreduced silver (Ag0)fromAgCl [2] which could also be evidence for the existenceof Ag0 in the composite To further explore the band gap (119864
119892)
of samples the classical Tauc equation (1) was employed asfollows
120572119864photon = 119870 (119864photon minus 119864119892)1198992
119864photon = ℎ](1)
where 120572 ℎ ] and 119870 are the absorption coefficient thePlanck constant the irradiation frequency and the constantfor semiconductors (usually equal to 1) respectively Theconstant 119899 depends on the type of band gap where 119899 = 1is for direct transition and 119899 = 4 is for indirect transitionThe band gap of the as-prepared Bi
2WO6in this work is
characteristic of a direct transition (Figure 7) so 119899 is equal
International Journal of Photoenergy 5
O 1s
Ag 3dC 1s
Cl 2p W 4f
Bi 4fIn
tens
ity (a
u)
02004006008001000
Binding energy (eV)
(a)
15919 eV
16450 eV
Bi 4f72
Bi 4f52
Bi 4f
Inte
nsity
(au
)
168 166 164 162 160 158 156 154170
Binding energy (eV)
(b)
3757 eV W 4f52
3541 eVW 4f72
W 4f
Inte
nsity
(au
)
38 36 34 3240
Binding energy (eV)
(c)
O 1s53028 eV
O 1s (W-O amp Bi-O)
O 1s (minusOH)53128 eV
O 1s (H2O)53196 eV
Inte
nsity
(au
)
528530532534
Binding energy (eV)
(d)
Ag 3d
3d52
3d32
36730 eV
37339 eV
37439 eV 36832 eV
Inte
nsity
(au
)
376 374 372 370 368 366 364378
Binding energy (eV)
(e)
19946 eV Cl 2p12
Cl 2p32Cl 2p
19783 eV
Inte
nsity
(au
)
200202 196198
Binding energy (eV)
(f)
Figure 3 XPS spectra of AgAgCl (10wt)-Bi2WO6composite (a) survey spectra and high-resolution orbits scan of (b) Bi 4f (c) W 4f (d)
O 1s (e) Ag 3d and (f) Cl 2p
6 International Journal of Photoenergy
1120583m
(a)
1120583m
(b)
Ag010nm
20nm
AgAgCl
Bi2WO6
(c)
Figure 4 SEM images of pure Bi2WO6(a) and AgAgCl (10wt)-Bi
2WO6composite (b) and TEM images of AgAgCl (10wt)-Bi
2WO6
composite (c)
Cl
ClCl
C
O
W
W
Bi Bi
Inte
nsity
(au
)
AgAg
1 2 3 4 50
Energy (keV)
Figure 5 EDS of AgAgCl (10wt)-Bi2WO6composite
to 4 By plotting (120572119864photon)12 versus 119864photon as illustrated
in Figure 6(b) the intercept at the horizontal axis is theband gap value This indicates that AgAgCl in compositesnarrowed the band gap from 270 eV to 257 eV comparedto pure Bi
2WO6 which could widen the edge wavelength
of incidence from 4593 nm to 4825 nm This indicates that
AgAgCl-Bi2WO6composites could be effectively activated
under visible-light irradiation
34 Photocatalytic Activity Test under Visible Light Photo-catalytic activities of as-prepared samples were tested bydegrading RhB (10mgL) All of the screening test resultsare plotted in Figure 8 The removal efficiencies for pureBi2WO6and AgAgCl were 388 and 653 in 45min
respectively By increasing the loading amount of AgAgCl inthe composites from 1wt to 10wt removal efficiencies ofthe composites were increased up to 100 after 45min undervisible light This enhancement effect may be attributed tothe establishment of a heterojunction between AgAgCl andBi2WO6[3 14 23] However further increasing the amount
of AgAgCl in the composites deteriorates the photocatalyticdegradation performances This may be interpreted as largernanoparticles which are loaded onto Bi
2WO6possibly weak-
ening the anchoring forces between them and destroying theheterostructure
Langmuir-Hinshelwood kinetic analysis was applied toRhB degradation in the presence of as-prepared photocata-lysts Trials performed with diluted concentrations of RhB(119888119900lt 10minus3molL) showed that the Langmuir-Hinshelwood
International Journal of Photoenergy 7
Bi2WO6
Bi2WO6AgAgCl-AgAgCl
Abso
rban
ce (a
u)
500400 600300 550350 450
Wavelength (nm)
(a)
Bi2WO6
Bi2WO6AgAgCl-
(120572timesE
phot
on)12
30 35 402520
Ephoton (eV)
(b)
Figure 6 (a) UV-Vis diffused reflectance spectra and (b) (120572119864photon)12-119864photon curves of as-prepared pure Bi
2WO6 AgAgCl and AgAgCl
(10wt)-Bi2WO6
G Z T Y S X U Rminus10
minus5
0
5
Band
ener
gy (e
V)
Figure 7 Band gap of Bi2WO6(simulated by Quantum Espresso
[22])
model could be simplified to a pseudo-first-order reactionmodel [24] expressed as follows
ln(119888119900
119888) = 119896119903times 119870 times 119905 = 119896
1015840119905 (2)
where 119905 119888119900 and 119888 are the time the initial concentration and
concentration at each specific reaction time 119905 of RhB 119896119903is
the reaction rate constant 119870 is the adsorption coefficient ofthe pollutant on the photocatalyst and 1198961015840 is pseudo-first-order reaction kinetics constant used as the parameter toevaluate the performances of as-prepared photocatalysts indegrading pollutants A plot of ln(119888
119900119888) as a function 119905 is
found in Figure 9 where the slope of the line of best fit is
1wt2wt4wt8wt
10wt20wtBi2WO6AgAgCl
39363330 42 4521 24 271512963 180
Time (min)
00
01
02
03
04
05
06
07
08
09
10
cc o
Figure 8 Photocatalytic degradation of RhB (10mgL) undervisible light with as-prepared pure Bi
2WO6 AgAgCl andAgAgCl-
Bi2WO6composites
the pseudo-first-order kinetics constant the results of whichare summarized in Table 2 The excellent linearity of eachline of best fit indicates that the photocatalytic degradationof RhB under visible-light irradiation in the presence ofAgAgCl-Bi
2WO6follows first-order kinetics The process
carried out with pure Bi2WO6as the photocatalyst exhibited
8 International Journal of Photoenergy
Table 2 Pseudo-first-order reaction rate constants for various processes
Bi2WO6
1 wt 2wt 4wt 8wt 10wt 20wt AgAgClPseudo-first-order119896 (10minus2minminus1) 1047 2733 3371 3930 4576 5688 4508 20371198772 09999 09961 09989 09979 09989 09993 09987 09939
Bi2WO6
1wt2wt4wt
8wt10wt20wtAgAgCl
3 6 90 18 2112 15
Time (min)
00
02
04
06
08
10
12
14
c oc
)ln
(
Figure 9 Photocatalytic kinetics of each process
the lowest reaction constant while loading of AgAgCl ontoBi2WO6increased the constant up to 54 times compared
to that of pure Bi2WO6at 10 wt AgAgCl These results
confirm that the presence of AgAgCl in the compositessignificantly increases photocatalytic activity with regard tothe degradation of organic pollutants
The stepwise mechanism for the degradation of RhB wasobserved by taking UV-Vis spectra which are illustrated inFigure 10 In the inset table the positions of characteristicpeaks for each intermediate species are summarized [25] Itcan be concluded that twoprocesses of RhBdegradation existnamely deethylation and destruction of the aromatic ring Inthe deethylation process RhB is decomposed into NNN1015840-Triethyl-Rhodamine (TER) NN1015840-Diethyl-Rhodamine(DER) N-Ethyl-Rhodamine (MER) and Rhodamine theUV-Vis characteristic peaks of which are located at wave-lengths of 539 nm 522 nm 510 nm and 498 nm respectivelyIn the first 33min peak positions blue-shifted from 554 nmto 498 nm indicating that RhB degraded into RhodamineAfter that peak positions stabilized at 498 nm and graduallyreduced in intensity This may be attributed to the degrada-tion of Rhodamine into smaller species such asH
2OandCO
2
The photocatalytic activity with respect to the degra-dation of the colourless organic compound phenol wasinvestigated and is illustrated in Figure 11 These resultsaimed to confirm the increased photocatalytic activity in the
0min3min6min9min12min15min18min21min
24min27min30min33min36min39min42min45min
Dye 120582max (nm)
00
02
04
06
08
10
12
14
16
Abso
rban
ce (a
u)
600400 500 700300 450 650350 550
Wavelength (nm)
Rhodamine B
Rhodamine
NNN998400-Triethyl-Rhodamine (TER)
NN998400-Diethyl-Rhodamine (DER)N-Ethyl-Rhodamine (MER)
554
539
522
510
498
Figure 10 UV-Vis spectra of solutions taken during the photocat-alytic process in the presence of AgAgCl (10wt)-Bi
2WO6(inset
table shows characteristic wavelength for each intermediate speciesin water [25])
presence of the AgAgCl-Bi2WO6composite under visible
light attributed to the surface plasmon resonance effectinstead of photosensitization of the dye (RhB in this work)[26] The composite performed well in the degradation ofphenol (approximately 30 of phenol was converted in45min) which was a better performance than that exhibitedby pure Bi
2WO6(only about 5 of phenol was converted
in 45min) This confirmed that the enhancement effect ofloading AgAgCl onto Bi
2WO6exists under visible-light
irradiation
35 Roles of Radical Species Holes (h+) and free radicalsespecially ∙OH are regarded as the main oxidative species inphotocatalytic degradation of organic pollutants [27] In thisstudy EDTA-2Na and 2-Butanol were chosen as the hole andhydroxyl radical scavengers respectively [28] When holeswere quenched only 15 of RhB was removed (Figure 12)Comparatively there was little influence when 2-Butanolwas added to quench hydroxyl radicals This suggests thatthe hydroxyl radical is not the main oxidative species in
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
4 International Journal of Photoenergy
Self-aggregation Ostwald ripening Self-organization
Scheme 1 Potential mechanism of forming the hierarchical flower-like superstructure of Bi2WO6
27 28 29 30 53 54 55 56 57 58378 380 382 384 386 388
30 20 40 50 60 70
AgCl (PDF 00-006-0480)
2120579 (deg)
2120579 (deg) 2120579 (deg) 2120579 (deg)
(a)
(a)
(b)
(b)
(c)
(c)
Inte
nsity
(au
)
00-039-0256)Bi2WO6 (PDFAg (PDF 01-087-0719) AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Figure 2 XRD pattern of AgAgCl (10wt)-Bi2WO6
in the composite were found which further confirms thesuccessful synthesis of AgAgCl-Bi
2WO6in this work
33 UV-Vis Diffused Reflectance Spectra (DRS) The opticalabsorbent properties of the AgAgCl-Bi
2WO6composite
were measured using UV-Vis diffused reflectance spec-troscopy Spectra of pure Bi
2WO6 AgAgCl and AgAgCl
(10 wt)-Bi2WO6are illustrated in Figure 6(a) After loading
AgAgCl onto Bi2WO6 the absorbent ability of the photocat-
alyst in the visible-light range was enhanced This is mainlydue to the plasmon resonance of photoreduced silver (Ag0)fromAgCl [2] which could also be evidence for the existenceof Ag0 in the composite To further explore the band gap (119864
119892)
of samples the classical Tauc equation (1) was employed asfollows
120572119864photon = 119870 (119864photon minus 119864119892)1198992
119864photon = ℎ](1)
where 120572 ℎ ] and 119870 are the absorption coefficient thePlanck constant the irradiation frequency and the constantfor semiconductors (usually equal to 1) respectively Theconstant 119899 depends on the type of band gap where 119899 = 1is for direct transition and 119899 = 4 is for indirect transitionThe band gap of the as-prepared Bi
2WO6in this work is
characteristic of a direct transition (Figure 7) so 119899 is equal
International Journal of Photoenergy 5
O 1s
Ag 3dC 1s
Cl 2p W 4f
Bi 4fIn
tens
ity (a
u)
02004006008001000
Binding energy (eV)
(a)
15919 eV
16450 eV
Bi 4f72
Bi 4f52
Bi 4f
Inte
nsity
(au
)
168 166 164 162 160 158 156 154170
Binding energy (eV)
(b)
3757 eV W 4f52
3541 eVW 4f72
W 4f
Inte
nsity
(au
)
38 36 34 3240
Binding energy (eV)
(c)
O 1s53028 eV
O 1s (W-O amp Bi-O)
O 1s (minusOH)53128 eV
O 1s (H2O)53196 eV
Inte
nsity
(au
)
528530532534
Binding energy (eV)
(d)
Ag 3d
3d52
3d32
36730 eV
37339 eV
37439 eV 36832 eV
Inte
nsity
(au
)
376 374 372 370 368 366 364378
Binding energy (eV)
(e)
19946 eV Cl 2p12
Cl 2p32Cl 2p
19783 eV
Inte
nsity
(au
)
200202 196198
Binding energy (eV)
(f)
Figure 3 XPS spectra of AgAgCl (10wt)-Bi2WO6composite (a) survey spectra and high-resolution orbits scan of (b) Bi 4f (c) W 4f (d)
O 1s (e) Ag 3d and (f) Cl 2p
6 International Journal of Photoenergy
1120583m
(a)
1120583m
(b)
Ag010nm
20nm
AgAgCl
Bi2WO6
(c)
Figure 4 SEM images of pure Bi2WO6(a) and AgAgCl (10wt)-Bi
2WO6composite (b) and TEM images of AgAgCl (10wt)-Bi
2WO6
composite (c)
Cl
ClCl
C
O
W
W
Bi Bi
Inte
nsity
(au
)
AgAg
1 2 3 4 50
Energy (keV)
Figure 5 EDS of AgAgCl (10wt)-Bi2WO6composite
to 4 By plotting (120572119864photon)12 versus 119864photon as illustrated
in Figure 6(b) the intercept at the horizontal axis is theband gap value This indicates that AgAgCl in compositesnarrowed the band gap from 270 eV to 257 eV comparedto pure Bi
2WO6 which could widen the edge wavelength
of incidence from 4593 nm to 4825 nm This indicates that
AgAgCl-Bi2WO6composites could be effectively activated
under visible-light irradiation
34 Photocatalytic Activity Test under Visible Light Photo-catalytic activities of as-prepared samples were tested bydegrading RhB (10mgL) All of the screening test resultsare plotted in Figure 8 The removal efficiencies for pureBi2WO6and AgAgCl were 388 and 653 in 45min
respectively By increasing the loading amount of AgAgCl inthe composites from 1wt to 10wt removal efficiencies ofthe composites were increased up to 100 after 45min undervisible light This enhancement effect may be attributed tothe establishment of a heterojunction between AgAgCl andBi2WO6[3 14 23] However further increasing the amount
of AgAgCl in the composites deteriorates the photocatalyticdegradation performances This may be interpreted as largernanoparticles which are loaded onto Bi
2WO6possibly weak-
ening the anchoring forces between them and destroying theheterostructure
Langmuir-Hinshelwood kinetic analysis was applied toRhB degradation in the presence of as-prepared photocata-lysts Trials performed with diluted concentrations of RhB(119888119900lt 10minus3molL) showed that the Langmuir-Hinshelwood
International Journal of Photoenergy 7
Bi2WO6
Bi2WO6AgAgCl-AgAgCl
Abso
rban
ce (a
u)
500400 600300 550350 450
Wavelength (nm)
(a)
Bi2WO6
Bi2WO6AgAgCl-
(120572timesE
phot
on)12
30 35 402520
Ephoton (eV)
(b)
Figure 6 (a) UV-Vis diffused reflectance spectra and (b) (120572119864photon)12-119864photon curves of as-prepared pure Bi
2WO6 AgAgCl and AgAgCl
(10wt)-Bi2WO6
G Z T Y S X U Rminus10
minus5
0
5
Band
ener
gy (e
V)
Figure 7 Band gap of Bi2WO6(simulated by Quantum Espresso
[22])
model could be simplified to a pseudo-first-order reactionmodel [24] expressed as follows
ln(119888119900
119888) = 119896119903times 119870 times 119905 = 119896
1015840119905 (2)
where 119905 119888119900 and 119888 are the time the initial concentration and
concentration at each specific reaction time 119905 of RhB 119896119903is
the reaction rate constant 119870 is the adsorption coefficient ofthe pollutant on the photocatalyst and 1198961015840 is pseudo-first-order reaction kinetics constant used as the parameter toevaluate the performances of as-prepared photocatalysts indegrading pollutants A plot of ln(119888
119900119888) as a function 119905 is
found in Figure 9 where the slope of the line of best fit is
1wt2wt4wt8wt
10wt20wtBi2WO6AgAgCl
39363330 42 4521 24 271512963 180
Time (min)
00
01
02
03
04
05
06
07
08
09
10
cc o
Figure 8 Photocatalytic degradation of RhB (10mgL) undervisible light with as-prepared pure Bi
2WO6 AgAgCl andAgAgCl-
Bi2WO6composites
the pseudo-first-order kinetics constant the results of whichare summarized in Table 2 The excellent linearity of eachline of best fit indicates that the photocatalytic degradationof RhB under visible-light irradiation in the presence ofAgAgCl-Bi
2WO6follows first-order kinetics The process
carried out with pure Bi2WO6as the photocatalyst exhibited
8 International Journal of Photoenergy
Table 2 Pseudo-first-order reaction rate constants for various processes
Bi2WO6
1 wt 2wt 4wt 8wt 10wt 20wt AgAgClPseudo-first-order119896 (10minus2minminus1) 1047 2733 3371 3930 4576 5688 4508 20371198772 09999 09961 09989 09979 09989 09993 09987 09939
Bi2WO6
1wt2wt4wt
8wt10wt20wtAgAgCl
3 6 90 18 2112 15
Time (min)
00
02
04
06
08
10
12
14
c oc
)ln
(
Figure 9 Photocatalytic kinetics of each process
the lowest reaction constant while loading of AgAgCl ontoBi2WO6increased the constant up to 54 times compared
to that of pure Bi2WO6at 10 wt AgAgCl These results
confirm that the presence of AgAgCl in the compositessignificantly increases photocatalytic activity with regard tothe degradation of organic pollutants
The stepwise mechanism for the degradation of RhB wasobserved by taking UV-Vis spectra which are illustrated inFigure 10 In the inset table the positions of characteristicpeaks for each intermediate species are summarized [25] Itcan be concluded that twoprocesses of RhBdegradation existnamely deethylation and destruction of the aromatic ring Inthe deethylation process RhB is decomposed into NNN1015840-Triethyl-Rhodamine (TER) NN1015840-Diethyl-Rhodamine(DER) N-Ethyl-Rhodamine (MER) and Rhodamine theUV-Vis characteristic peaks of which are located at wave-lengths of 539 nm 522 nm 510 nm and 498 nm respectivelyIn the first 33min peak positions blue-shifted from 554 nmto 498 nm indicating that RhB degraded into RhodamineAfter that peak positions stabilized at 498 nm and graduallyreduced in intensity This may be attributed to the degrada-tion of Rhodamine into smaller species such asH
2OandCO
2
The photocatalytic activity with respect to the degra-dation of the colourless organic compound phenol wasinvestigated and is illustrated in Figure 11 These resultsaimed to confirm the increased photocatalytic activity in the
0min3min6min9min12min15min18min21min
24min27min30min33min36min39min42min45min
Dye 120582max (nm)
00
02
04
06
08
10
12
14
16
Abso
rban
ce (a
u)
600400 500 700300 450 650350 550
Wavelength (nm)
Rhodamine B
Rhodamine
NNN998400-Triethyl-Rhodamine (TER)
NN998400-Diethyl-Rhodamine (DER)N-Ethyl-Rhodamine (MER)
554
539
522
510
498
Figure 10 UV-Vis spectra of solutions taken during the photocat-alytic process in the presence of AgAgCl (10wt)-Bi
2WO6(inset
table shows characteristic wavelength for each intermediate speciesin water [25])
presence of the AgAgCl-Bi2WO6composite under visible
light attributed to the surface plasmon resonance effectinstead of photosensitization of the dye (RhB in this work)[26] The composite performed well in the degradation ofphenol (approximately 30 of phenol was converted in45min) which was a better performance than that exhibitedby pure Bi
2WO6(only about 5 of phenol was converted
in 45min) This confirmed that the enhancement effect ofloading AgAgCl onto Bi
2WO6exists under visible-light
irradiation
35 Roles of Radical Species Holes (h+) and free radicalsespecially ∙OH are regarded as the main oxidative species inphotocatalytic degradation of organic pollutants [27] In thisstudy EDTA-2Na and 2-Butanol were chosen as the hole andhydroxyl radical scavengers respectively [28] When holeswere quenched only 15 of RhB was removed (Figure 12)Comparatively there was little influence when 2-Butanolwas added to quench hydroxyl radicals This suggests thatthe hydroxyl radical is not the main oxidative species in
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 5
O 1s
Ag 3dC 1s
Cl 2p W 4f
Bi 4fIn
tens
ity (a
u)
02004006008001000
Binding energy (eV)
(a)
15919 eV
16450 eV
Bi 4f72
Bi 4f52
Bi 4f
Inte
nsity
(au
)
168 166 164 162 160 158 156 154170
Binding energy (eV)
(b)
3757 eV W 4f52
3541 eVW 4f72
W 4f
Inte
nsity
(au
)
38 36 34 3240
Binding energy (eV)
(c)
O 1s53028 eV
O 1s (W-O amp Bi-O)
O 1s (minusOH)53128 eV
O 1s (H2O)53196 eV
Inte
nsity
(au
)
528530532534
Binding energy (eV)
(d)
Ag 3d
3d52
3d32
36730 eV
37339 eV
37439 eV 36832 eV
Inte
nsity
(au
)
376 374 372 370 368 366 364378
Binding energy (eV)
(e)
19946 eV Cl 2p12
Cl 2p32Cl 2p
19783 eV
Inte
nsity
(au
)
200202 196198
Binding energy (eV)
(f)
Figure 3 XPS spectra of AgAgCl (10wt)-Bi2WO6composite (a) survey spectra and high-resolution orbits scan of (b) Bi 4f (c) W 4f (d)
O 1s (e) Ag 3d and (f) Cl 2p
6 International Journal of Photoenergy
1120583m
(a)
1120583m
(b)
Ag010nm
20nm
AgAgCl
Bi2WO6
(c)
Figure 4 SEM images of pure Bi2WO6(a) and AgAgCl (10wt)-Bi
2WO6composite (b) and TEM images of AgAgCl (10wt)-Bi
2WO6
composite (c)
Cl
ClCl
C
O
W
W
Bi Bi
Inte
nsity
(au
)
AgAg
1 2 3 4 50
Energy (keV)
Figure 5 EDS of AgAgCl (10wt)-Bi2WO6composite
to 4 By plotting (120572119864photon)12 versus 119864photon as illustrated
in Figure 6(b) the intercept at the horizontal axis is theband gap value This indicates that AgAgCl in compositesnarrowed the band gap from 270 eV to 257 eV comparedto pure Bi
2WO6 which could widen the edge wavelength
of incidence from 4593 nm to 4825 nm This indicates that
AgAgCl-Bi2WO6composites could be effectively activated
under visible-light irradiation
34 Photocatalytic Activity Test under Visible Light Photo-catalytic activities of as-prepared samples were tested bydegrading RhB (10mgL) All of the screening test resultsare plotted in Figure 8 The removal efficiencies for pureBi2WO6and AgAgCl were 388 and 653 in 45min
respectively By increasing the loading amount of AgAgCl inthe composites from 1wt to 10wt removal efficiencies ofthe composites were increased up to 100 after 45min undervisible light This enhancement effect may be attributed tothe establishment of a heterojunction between AgAgCl andBi2WO6[3 14 23] However further increasing the amount
of AgAgCl in the composites deteriorates the photocatalyticdegradation performances This may be interpreted as largernanoparticles which are loaded onto Bi
2WO6possibly weak-
ening the anchoring forces between them and destroying theheterostructure
Langmuir-Hinshelwood kinetic analysis was applied toRhB degradation in the presence of as-prepared photocata-lysts Trials performed with diluted concentrations of RhB(119888119900lt 10minus3molL) showed that the Langmuir-Hinshelwood
International Journal of Photoenergy 7
Bi2WO6
Bi2WO6AgAgCl-AgAgCl
Abso
rban
ce (a
u)
500400 600300 550350 450
Wavelength (nm)
(a)
Bi2WO6
Bi2WO6AgAgCl-
(120572timesE
phot
on)12
30 35 402520
Ephoton (eV)
(b)
Figure 6 (a) UV-Vis diffused reflectance spectra and (b) (120572119864photon)12-119864photon curves of as-prepared pure Bi
2WO6 AgAgCl and AgAgCl
(10wt)-Bi2WO6
G Z T Y S X U Rminus10
minus5
0
5
Band
ener
gy (e
V)
Figure 7 Band gap of Bi2WO6(simulated by Quantum Espresso
[22])
model could be simplified to a pseudo-first-order reactionmodel [24] expressed as follows
ln(119888119900
119888) = 119896119903times 119870 times 119905 = 119896
1015840119905 (2)
where 119905 119888119900 and 119888 are the time the initial concentration and
concentration at each specific reaction time 119905 of RhB 119896119903is
the reaction rate constant 119870 is the adsorption coefficient ofthe pollutant on the photocatalyst and 1198961015840 is pseudo-first-order reaction kinetics constant used as the parameter toevaluate the performances of as-prepared photocatalysts indegrading pollutants A plot of ln(119888
119900119888) as a function 119905 is
found in Figure 9 where the slope of the line of best fit is
1wt2wt4wt8wt
10wt20wtBi2WO6AgAgCl
39363330 42 4521 24 271512963 180
Time (min)
00
01
02
03
04
05
06
07
08
09
10
cc o
Figure 8 Photocatalytic degradation of RhB (10mgL) undervisible light with as-prepared pure Bi
2WO6 AgAgCl andAgAgCl-
Bi2WO6composites
the pseudo-first-order kinetics constant the results of whichare summarized in Table 2 The excellent linearity of eachline of best fit indicates that the photocatalytic degradationof RhB under visible-light irradiation in the presence ofAgAgCl-Bi
2WO6follows first-order kinetics The process
carried out with pure Bi2WO6as the photocatalyst exhibited
8 International Journal of Photoenergy
Table 2 Pseudo-first-order reaction rate constants for various processes
Bi2WO6
1 wt 2wt 4wt 8wt 10wt 20wt AgAgClPseudo-first-order119896 (10minus2minminus1) 1047 2733 3371 3930 4576 5688 4508 20371198772 09999 09961 09989 09979 09989 09993 09987 09939
Bi2WO6
1wt2wt4wt
8wt10wt20wtAgAgCl
3 6 90 18 2112 15
Time (min)
00
02
04
06
08
10
12
14
c oc
)ln
(
Figure 9 Photocatalytic kinetics of each process
the lowest reaction constant while loading of AgAgCl ontoBi2WO6increased the constant up to 54 times compared
to that of pure Bi2WO6at 10 wt AgAgCl These results
confirm that the presence of AgAgCl in the compositessignificantly increases photocatalytic activity with regard tothe degradation of organic pollutants
The stepwise mechanism for the degradation of RhB wasobserved by taking UV-Vis spectra which are illustrated inFigure 10 In the inset table the positions of characteristicpeaks for each intermediate species are summarized [25] Itcan be concluded that twoprocesses of RhBdegradation existnamely deethylation and destruction of the aromatic ring Inthe deethylation process RhB is decomposed into NNN1015840-Triethyl-Rhodamine (TER) NN1015840-Diethyl-Rhodamine(DER) N-Ethyl-Rhodamine (MER) and Rhodamine theUV-Vis characteristic peaks of which are located at wave-lengths of 539 nm 522 nm 510 nm and 498 nm respectivelyIn the first 33min peak positions blue-shifted from 554 nmto 498 nm indicating that RhB degraded into RhodamineAfter that peak positions stabilized at 498 nm and graduallyreduced in intensity This may be attributed to the degrada-tion of Rhodamine into smaller species such asH
2OandCO
2
The photocatalytic activity with respect to the degra-dation of the colourless organic compound phenol wasinvestigated and is illustrated in Figure 11 These resultsaimed to confirm the increased photocatalytic activity in the
0min3min6min9min12min15min18min21min
24min27min30min33min36min39min42min45min
Dye 120582max (nm)
00
02
04
06
08
10
12
14
16
Abso
rban
ce (a
u)
600400 500 700300 450 650350 550
Wavelength (nm)
Rhodamine B
Rhodamine
NNN998400-Triethyl-Rhodamine (TER)
NN998400-Diethyl-Rhodamine (DER)N-Ethyl-Rhodamine (MER)
554
539
522
510
498
Figure 10 UV-Vis spectra of solutions taken during the photocat-alytic process in the presence of AgAgCl (10wt)-Bi
2WO6(inset
table shows characteristic wavelength for each intermediate speciesin water [25])
presence of the AgAgCl-Bi2WO6composite under visible
light attributed to the surface plasmon resonance effectinstead of photosensitization of the dye (RhB in this work)[26] The composite performed well in the degradation ofphenol (approximately 30 of phenol was converted in45min) which was a better performance than that exhibitedby pure Bi
2WO6(only about 5 of phenol was converted
in 45min) This confirmed that the enhancement effect ofloading AgAgCl onto Bi
2WO6exists under visible-light
irradiation
35 Roles of Radical Species Holes (h+) and free radicalsespecially ∙OH are regarded as the main oxidative species inphotocatalytic degradation of organic pollutants [27] In thisstudy EDTA-2Na and 2-Butanol were chosen as the hole andhydroxyl radical scavengers respectively [28] When holeswere quenched only 15 of RhB was removed (Figure 12)Comparatively there was little influence when 2-Butanolwas added to quench hydroxyl radicals This suggests thatthe hydroxyl radical is not the main oxidative species in
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
6 International Journal of Photoenergy
1120583m
(a)
1120583m
(b)
Ag010nm
20nm
AgAgCl
Bi2WO6
(c)
Figure 4 SEM images of pure Bi2WO6(a) and AgAgCl (10wt)-Bi
2WO6composite (b) and TEM images of AgAgCl (10wt)-Bi
2WO6
composite (c)
Cl
ClCl
C
O
W
W
Bi Bi
Inte
nsity
(au
)
AgAg
1 2 3 4 50
Energy (keV)
Figure 5 EDS of AgAgCl (10wt)-Bi2WO6composite
to 4 By plotting (120572119864photon)12 versus 119864photon as illustrated
in Figure 6(b) the intercept at the horizontal axis is theband gap value This indicates that AgAgCl in compositesnarrowed the band gap from 270 eV to 257 eV comparedto pure Bi
2WO6 which could widen the edge wavelength
of incidence from 4593 nm to 4825 nm This indicates that
AgAgCl-Bi2WO6composites could be effectively activated
under visible-light irradiation
34 Photocatalytic Activity Test under Visible Light Photo-catalytic activities of as-prepared samples were tested bydegrading RhB (10mgL) All of the screening test resultsare plotted in Figure 8 The removal efficiencies for pureBi2WO6and AgAgCl were 388 and 653 in 45min
respectively By increasing the loading amount of AgAgCl inthe composites from 1wt to 10wt removal efficiencies ofthe composites were increased up to 100 after 45min undervisible light This enhancement effect may be attributed tothe establishment of a heterojunction between AgAgCl andBi2WO6[3 14 23] However further increasing the amount
of AgAgCl in the composites deteriorates the photocatalyticdegradation performances This may be interpreted as largernanoparticles which are loaded onto Bi
2WO6possibly weak-
ening the anchoring forces between them and destroying theheterostructure
Langmuir-Hinshelwood kinetic analysis was applied toRhB degradation in the presence of as-prepared photocata-lysts Trials performed with diluted concentrations of RhB(119888119900lt 10minus3molL) showed that the Langmuir-Hinshelwood
International Journal of Photoenergy 7
Bi2WO6
Bi2WO6AgAgCl-AgAgCl
Abso
rban
ce (a
u)
500400 600300 550350 450
Wavelength (nm)
(a)
Bi2WO6
Bi2WO6AgAgCl-
(120572timesE
phot
on)12
30 35 402520
Ephoton (eV)
(b)
Figure 6 (a) UV-Vis diffused reflectance spectra and (b) (120572119864photon)12-119864photon curves of as-prepared pure Bi
2WO6 AgAgCl and AgAgCl
(10wt)-Bi2WO6
G Z T Y S X U Rminus10
minus5
0
5
Band
ener
gy (e
V)
Figure 7 Band gap of Bi2WO6(simulated by Quantum Espresso
[22])
model could be simplified to a pseudo-first-order reactionmodel [24] expressed as follows
ln(119888119900
119888) = 119896119903times 119870 times 119905 = 119896
1015840119905 (2)
where 119905 119888119900 and 119888 are the time the initial concentration and
concentration at each specific reaction time 119905 of RhB 119896119903is
the reaction rate constant 119870 is the adsorption coefficient ofthe pollutant on the photocatalyst and 1198961015840 is pseudo-first-order reaction kinetics constant used as the parameter toevaluate the performances of as-prepared photocatalysts indegrading pollutants A plot of ln(119888
119900119888) as a function 119905 is
found in Figure 9 where the slope of the line of best fit is
1wt2wt4wt8wt
10wt20wtBi2WO6AgAgCl
39363330 42 4521 24 271512963 180
Time (min)
00
01
02
03
04
05
06
07
08
09
10
cc o
Figure 8 Photocatalytic degradation of RhB (10mgL) undervisible light with as-prepared pure Bi
2WO6 AgAgCl andAgAgCl-
Bi2WO6composites
the pseudo-first-order kinetics constant the results of whichare summarized in Table 2 The excellent linearity of eachline of best fit indicates that the photocatalytic degradationof RhB under visible-light irradiation in the presence ofAgAgCl-Bi
2WO6follows first-order kinetics The process
carried out with pure Bi2WO6as the photocatalyst exhibited
8 International Journal of Photoenergy
Table 2 Pseudo-first-order reaction rate constants for various processes
Bi2WO6
1 wt 2wt 4wt 8wt 10wt 20wt AgAgClPseudo-first-order119896 (10minus2minminus1) 1047 2733 3371 3930 4576 5688 4508 20371198772 09999 09961 09989 09979 09989 09993 09987 09939
Bi2WO6
1wt2wt4wt
8wt10wt20wtAgAgCl
3 6 90 18 2112 15
Time (min)
00
02
04
06
08
10
12
14
c oc
)ln
(
Figure 9 Photocatalytic kinetics of each process
the lowest reaction constant while loading of AgAgCl ontoBi2WO6increased the constant up to 54 times compared
to that of pure Bi2WO6at 10 wt AgAgCl These results
confirm that the presence of AgAgCl in the compositessignificantly increases photocatalytic activity with regard tothe degradation of organic pollutants
The stepwise mechanism for the degradation of RhB wasobserved by taking UV-Vis spectra which are illustrated inFigure 10 In the inset table the positions of characteristicpeaks for each intermediate species are summarized [25] Itcan be concluded that twoprocesses of RhBdegradation existnamely deethylation and destruction of the aromatic ring Inthe deethylation process RhB is decomposed into NNN1015840-Triethyl-Rhodamine (TER) NN1015840-Diethyl-Rhodamine(DER) N-Ethyl-Rhodamine (MER) and Rhodamine theUV-Vis characteristic peaks of which are located at wave-lengths of 539 nm 522 nm 510 nm and 498 nm respectivelyIn the first 33min peak positions blue-shifted from 554 nmto 498 nm indicating that RhB degraded into RhodamineAfter that peak positions stabilized at 498 nm and graduallyreduced in intensity This may be attributed to the degrada-tion of Rhodamine into smaller species such asH
2OandCO
2
The photocatalytic activity with respect to the degra-dation of the colourless organic compound phenol wasinvestigated and is illustrated in Figure 11 These resultsaimed to confirm the increased photocatalytic activity in the
0min3min6min9min12min15min18min21min
24min27min30min33min36min39min42min45min
Dye 120582max (nm)
00
02
04
06
08
10
12
14
16
Abso
rban
ce (a
u)
600400 500 700300 450 650350 550
Wavelength (nm)
Rhodamine B
Rhodamine
NNN998400-Triethyl-Rhodamine (TER)
NN998400-Diethyl-Rhodamine (DER)N-Ethyl-Rhodamine (MER)
554
539
522
510
498
Figure 10 UV-Vis spectra of solutions taken during the photocat-alytic process in the presence of AgAgCl (10wt)-Bi
2WO6(inset
table shows characteristic wavelength for each intermediate speciesin water [25])
presence of the AgAgCl-Bi2WO6composite under visible
light attributed to the surface plasmon resonance effectinstead of photosensitization of the dye (RhB in this work)[26] The composite performed well in the degradation ofphenol (approximately 30 of phenol was converted in45min) which was a better performance than that exhibitedby pure Bi
2WO6(only about 5 of phenol was converted
in 45min) This confirmed that the enhancement effect ofloading AgAgCl onto Bi
2WO6exists under visible-light
irradiation
35 Roles of Radical Species Holes (h+) and free radicalsespecially ∙OH are regarded as the main oxidative species inphotocatalytic degradation of organic pollutants [27] In thisstudy EDTA-2Na and 2-Butanol were chosen as the hole andhydroxyl radical scavengers respectively [28] When holeswere quenched only 15 of RhB was removed (Figure 12)Comparatively there was little influence when 2-Butanolwas added to quench hydroxyl radicals This suggests thatthe hydroxyl radical is not the main oxidative species in
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 7
Bi2WO6
Bi2WO6AgAgCl-AgAgCl
Abso
rban
ce (a
u)
500400 600300 550350 450
Wavelength (nm)
(a)
Bi2WO6
Bi2WO6AgAgCl-
(120572timesE
phot
on)12
30 35 402520
Ephoton (eV)
(b)
Figure 6 (a) UV-Vis diffused reflectance spectra and (b) (120572119864photon)12-119864photon curves of as-prepared pure Bi
2WO6 AgAgCl and AgAgCl
(10wt)-Bi2WO6
G Z T Y S X U Rminus10
minus5
0
5
Band
ener
gy (e
V)
Figure 7 Band gap of Bi2WO6(simulated by Quantum Espresso
[22])
model could be simplified to a pseudo-first-order reactionmodel [24] expressed as follows
ln(119888119900
119888) = 119896119903times 119870 times 119905 = 119896
1015840119905 (2)
where 119905 119888119900 and 119888 are the time the initial concentration and
concentration at each specific reaction time 119905 of RhB 119896119903is
the reaction rate constant 119870 is the adsorption coefficient ofthe pollutant on the photocatalyst and 1198961015840 is pseudo-first-order reaction kinetics constant used as the parameter toevaluate the performances of as-prepared photocatalysts indegrading pollutants A plot of ln(119888
119900119888) as a function 119905 is
found in Figure 9 where the slope of the line of best fit is
1wt2wt4wt8wt
10wt20wtBi2WO6AgAgCl
39363330 42 4521 24 271512963 180
Time (min)
00
01
02
03
04
05
06
07
08
09
10
cc o
Figure 8 Photocatalytic degradation of RhB (10mgL) undervisible light with as-prepared pure Bi
2WO6 AgAgCl andAgAgCl-
Bi2WO6composites
the pseudo-first-order kinetics constant the results of whichare summarized in Table 2 The excellent linearity of eachline of best fit indicates that the photocatalytic degradationof RhB under visible-light irradiation in the presence ofAgAgCl-Bi
2WO6follows first-order kinetics The process
carried out with pure Bi2WO6as the photocatalyst exhibited
8 International Journal of Photoenergy
Table 2 Pseudo-first-order reaction rate constants for various processes
Bi2WO6
1 wt 2wt 4wt 8wt 10wt 20wt AgAgClPseudo-first-order119896 (10minus2minminus1) 1047 2733 3371 3930 4576 5688 4508 20371198772 09999 09961 09989 09979 09989 09993 09987 09939
Bi2WO6
1wt2wt4wt
8wt10wt20wtAgAgCl
3 6 90 18 2112 15
Time (min)
00
02
04
06
08
10
12
14
c oc
)ln
(
Figure 9 Photocatalytic kinetics of each process
the lowest reaction constant while loading of AgAgCl ontoBi2WO6increased the constant up to 54 times compared
to that of pure Bi2WO6at 10 wt AgAgCl These results
confirm that the presence of AgAgCl in the compositessignificantly increases photocatalytic activity with regard tothe degradation of organic pollutants
The stepwise mechanism for the degradation of RhB wasobserved by taking UV-Vis spectra which are illustrated inFigure 10 In the inset table the positions of characteristicpeaks for each intermediate species are summarized [25] Itcan be concluded that twoprocesses of RhBdegradation existnamely deethylation and destruction of the aromatic ring Inthe deethylation process RhB is decomposed into NNN1015840-Triethyl-Rhodamine (TER) NN1015840-Diethyl-Rhodamine(DER) N-Ethyl-Rhodamine (MER) and Rhodamine theUV-Vis characteristic peaks of which are located at wave-lengths of 539 nm 522 nm 510 nm and 498 nm respectivelyIn the first 33min peak positions blue-shifted from 554 nmto 498 nm indicating that RhB degraded into RhodamineAfter that peak positions stabilized at 498 nm and graduallyreduced in intensity This may be attributed to the degrada-tion of Rhodamine into smaller species such asH
2OandCO
2
The photocatalytic activity with respect to the degra-dation of the colourless organic compound phenol wasinvestigated and is illustrated in Figure 11 These resultsaimed to confirm the increased photocatalytic activity in the
0min3min6min9min12min15min18min21min
24min27min30min33min36min39min42min45min
Dye 120582max (nm)
00
02
04
06
08
10
12
14
16
Abso
rban
ce (a
u)
600400 500 700300 450 650350 550
Wavelength (nm)
Rhodamine B
Rhodamine
NNN998400-Triethyl-Rhodamine (TER)
NN998400-Diethyl-Rhodamine (DER)N-Ethyl-Rhodamine (MER)
554
539
522
510
498
Figure 10 UV-Vis spectra of solutions taken during the photocat-alytic process in the presence of AgAgCl (10wt)-Bi
2WO6(inset
table shows characteristic wavelength for each intermediate speciesin water [25])
presence of the AgAgCl-Bi2WO6composite under visible
light attributed to the surface plasmon resonance effectinstead of photosensitization of the dye (RhB in this work)[26] The composite performed well in the degradation ofphenol (approximately 30 of phenol was converted in45min) which was a better performance than that exhibitedby pure Bi
2WO6(only about 5 of phenol was converted
in 45min) This confirmed that the enhancement effect ofloading AgAgCl onto Bi
2WO6exists under visible-light
irradiation
35 Roles of Radical Species Holes (h+) and free radicalsespecially ∙OH are regarded as the main oxidative species inphotocatalytic degradation of organic pollutants [27] In thisstudy EDTA-2Na and 2-Butanol were chosen as the hole andhydroxyl radical scavengers respectively [28] When holeswere quenched only 15 of RhB was removed (Figure 12)Comparatively there was little influence when 2-Butanolwas added to quench hydroxyl radicals This suggests thatthe hydroxyl radical is not the main oxidative species in
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
8 International Journal of Photoenergy
Table 2 Pseudo-first-order reaction rate constants for various processes
Bi2WO6
1 wt 2wt 4wt 8wt 10wt 20wt AgAgClPseudo-first-order119896 (10minus2minminus1) 1047 2733 3371 3930 4576 5688 4508 20371198772 09999 09961 09989 09979 09989 09993 09987 09939
Bi2WO6
1wt2wt4wt
8wt10wt20wtAgAgCl
3 6 90 18 2112 15
Time (min)
00
02
04
06
08
10
12
14
c oc
)ln
(
Figure 9 Photocatalytic kinetics of each process
the lowest reaction constant while loading of AgAgCl ontoBi2WO6increased the constant up to 54 times compared
to that of pure Bi2WO6at 10 wt AgAgCl These results
confirm that the presence of AgAgCl in the compositessignificantly increases photocatalytic activity with regard tothe degradation of organic pollutants
The stepwise mechanism for the degradation of RhB wasobserved by taking UV-Vis spectra which are illustrated inFigure 10 In the inset table the positions of characteristicpeaks for each intermediate species are summarized [25] Itcan be concluded that twoprocesses of RhBdegradation existnamely deethylation and destruction of the aromatic ring Inthe deethylation process RhB is decomposed into NNN1015840-Triethyl-Rhodamine (TER) NN1015840-Diethyl-Rhodamine(DER) N-Ethyl-Rhodamine (MER) and Rhodamine theUV-Vis characteristic peaks of which are located at wave-lengths of 539 nm 522 nm 510 nm and 498 nm respectivelyIn the first 33min peak positions blue-shifted from 554 nmto 498 nm indicating that RhB degraded into RhodamineAfter that peak positions stabilized at 498 nm and graduallyreduced in intensity This may be attributed to the degrada-tion of Rhodamine into smaller species such asH
2OandCO
2
The photocatalytic activity with respect to the degra-dation of the colourless organic compound phenol wasinvestigated and is illustrated in Figure 11 These resultsaimed to confirm the increased photocatalytic activity in the
0min3min6min9min12min15min18min21min
24min27min30min33min36min39min42min45min
Dye 120582max (nm)
00
02
04
06
08
10
12
14
16
Abso
rban
ce (a
u)
600400 500 700300 450 650350 550
Wavelength (nm)
Rhodamine B
Rhodamine
NNN998400-Triethyl-Rhodamine (TER)
NN998400-Diethyl-Rhodamine (DER)N-Ethyl-Rhodamine (MER)
554
539
522
510
498
Figure 10 UV-Vis spectra of solutions taken during the photocat-alytic process in the presence of AgAgCl (10wt)-Bi
2WO6(inset
table shows characteristic wavelength for each intermediate speciesin water [25])
presence of the AgAgCl-Bi2WO6composite under visible
light attributed to the surface plasmon resonance effectinstead of photosensitization of the dye (RhB in this work)[26] The composite performed well in the degradation ofphenol (approximately 30 of phenol was converted in45min) which was a better performance than that exhibitedby pure Bi
2WO6(only about 5 of phenol was converted
in 45min) This confirmed that the enhancement effect ofloading AgAgCl onto Bi
2WO6exists under visible-light
irradiation
35 Roles of Radical Species Holes (h+) and free radicalsespecially ∙OH are regarded as the main oxidative species inphotocatalytic degradation of organic pollutants [27] In thisstudy EDTA-2Na and 2-Butanol were chosen as the hole andhydroxyl radical scavengers respectively [28] When holeswere quenched only 15 of RhB was removed (Figure 12)Comparatively there was little influence when 2-Butanolwas added to quench hydroxyl radicals This suggests thatthe hydroxyl radical is not the main oxidative species in
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 9
Phenol ( 6)RhB (Phenol (Bi2WO6)
30 45150
Time (min)
00
02
04
06
08
10
cc o
Bi2WOAgAgCl-6)Bi2WOAgAgCl-
Figure 11 Degradation of phenol (10mgL) by using AgAgCl-Bi2WO6composite
00
02
04
06
08
10
cc o
EDTA-2Na (001molL)2-Butanol (001molL)
3 6 90 15 18 21 24 2712 33 36 39 42 4530
Time (min)
Bi2WO6AgAgCl-
Figure 12 Photocatalytic activity in presence of AgAgCl-Bi2WO6
and quenchers
the degradation of RhB and that holes govern the photocat-alytic process Similar results were also reported in the liter-ature [9 29] This phenomenon may be explained knowingthat the standard redox potential of Bi
2O4BiO+(BiVBiIII)
(+159 eV) is much more negative than that of ∙OHndashOH(+230 eV) [9 29] This suggests that ldquononselectiverdquo ∙OHcould not be produced in this photocatalytic oxidationprocess
36 Reusability Reusability is a significant parameterused to evaluate photocatalysts implemented in practical
(cominusc)c
o
978 953924 915
1 2 3 400
02
04
06
08
10
Figure 13 Removal efficiencies for 4 runs of 45min
Ag (PDF 01-087-0719)AgCl (PDF 00-006-0480)
00-039-0256)Bi2WO6 (PDF
Before
After
Inte
nsity
(au
)
310 320 330 340
378 380 382 384 386 388
20 25 35 40 45 50 55 60 65 7030
2120579 (deg)
(a)
(b)
Figure 14 XRD patterns of AgAgCl (10wt)-Bi2WO6before and
after 4 runs
applications As-prepared composites were investigatedby taking 4 runs where RhB was degraded Removalefficiencies after 45min were plotted in Figure 13 After 4runs the removal efficiency decreased slightly from 978to 915 but this relatively high removal efficiency stillimplies the high stability of the AgAgCl-Bi
2WO6composite
Furthermore used photocatalysts were observed by XRD thepatterns of which are shown in Figure 14 Lattice parametersof Bi2WO6after four runs were 119886 = 54577 A 119887 = 163970 A
and 119888 = 54505 A All the characteristic peaks of Bi2WO6
were found with high intensities indicating that the maincrystal structure of Bi
2WO6was stable and was not destroyed
during the recycle However the characteristic peaks of AgClwere observed with reduced intensities On the other handintensities of other peaks especially the peak at 2120579 = 382∘
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
10 International Journal of Photoenergy
AgCl
VBVB
CBCB
RhB
h
h
h
RhB
Oxidative species
Degradationproducts
AgRhB + O2
minus
O2
RhBlowastlowast
RhBlowast CO2 + H2O
Bi2WO6
40
35
30
25
20
15
10
05
00
minus05
minus10
minus15
Pote
ntia
l ver
sus N
HE
(eV
) eminus
h+
h+
Hole (h+)Electron (eminus)
Figure 15 Schematic of possible mechanism of degrading RhB in the presence of AgAgCl-Bi2WO6
(Figure 14(b)) for metallic Ag0 became stronger This maybe attributed to the reduction of AgCl to metallic Ag0 inthe photocatalytic process under visible-light irradiation asphotogenerated electrons are produced and easily react withAg+ This may be an explanation for the decreased removalefficiency of RhB Another possible explanation is that theintermediate species of RhB were adsorbed on the compositeand refractory to be degraded
37 Proposed Mechanism of Photocatalytic Degradation Theband structure of the AgAgCl-Bi
2WO6composite is illus-
trated in Figure 15 The proposed mechanism of using thecomposite to degrade RhB could be summarized as follows(1) Bi2WO6with a band gap of 270 eV is activated by visible-
light irradiation generating electrons and holes (2) Ag0nanoparticles induced by surface plasmon resonance undervisible light could produce electrons and leave holes on thevalence band [1] and electrons could rapidly transfer toBi2WO6or AgCl (3) RhB could be activated by photons
(photosensitization) and generate electrons which couldtransfer to the conduction band of either Bi
2WO6or AgCl
and (4) Clminus could be oxidized into a ∙Cl radical which issupposed to oxidize organic pollutants Holes on the valenceband of Bi
2WO6would transfer to that of AgCl and the
separation efficiency of photogenerated electrons and holeswould improve [30] Meanwhile electrons induced by thesurface plasmon resonance and photosensitization effectswould be beneficial to produce more oxidative species Theintegrated effect results in an enhanced photocatalytic activityto degrade organic pollutants
4 Conclusion
An AgAgCl-Bi2WO6composite was successfully synthe-
sized using a hydrothermal and photoreduced method Itsmorphology was hierarchical and flower-like with a size of
2-3 120583m As-prepared photocatalysts were performed withincreased photocatalytic activities and high stabilities whendegrading RhB under visible-light irradiation The 10wtAgAgCl sample exhibited the best performance A mecha-nism of photocatalytic oxidation was proposed and it wasdeduced that the enhancement effect is mainly due to theestablishment of a heterostructure as well as the surface plas-mon resonance and photosensitization effects This work isevidence for the potential application of plasmonic metals inphotocatalytic oxidation processes with enhancement effects
Competing Interests
The authors declare that they have no competing interests
Acknowledgments
Xiangchao Meng was financially supported by the ChinaScholarship Council (CSC) This work was financially sup-ported by the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC)
References
[1] S Linic P Christopher and D B Ingram ldquoPlasmonic-metalnanostructures for efficient conversion of solar to chemicalenergyrdquo Nature Materials vol 10 no 12 pp 911ndash921 2011
[2] P Wang B Huang X Qin et al ldquoAgAgCl a highly efficientand stable photocatalyst active under visible lightrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7931ndash79332008
[3] J Yu G Dai and B Huang ldquoFabrication and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
nanotube arraysrdquo The Journal of Physical Chemistry C vol 113no 37 pp 16394ndash16401 2009
[4] J Zhou Y Cheng and J Yu ldquoPreparation and characterizationof visible-light-driven plasmonic photocatalyst AgAgClTiO
2
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 11
nanocomposite thin filmsrdquo Journal of Photochemistry and Pho-tobiology A Chemistry vol 223 no 2-3 pp 82ndash87 2011
[5] L Ye J Liu C Gong L Tian T Peng and L Zan ldquoTwodifferent roles of metallic Ag on AgAgXBiOX (X=Cl Br)visible light photocatalysts surface plasmon resonance and Z-Scheme bridgerdquoACS Catalysis vol 2 no 8 pp 1677ndash1683 2012
[6] H Fu C Pan W Yao and Y Zhu ldquoVisible-light-induceddegradation of rhodamine B by nanosized Bi
2WO6rdquoThe Journal
of Physical Chemistry B vol 109 no 47 pp 22432ndash22439 2005[7] H An Y Du T Wang C Wang W Hao and J Zhang
ldquoPhotocatalytic properties of BiOX (X=Cl Br and I)rdquo RareMetals vol 27 no 3 pp 243ndash250 2008
[8] X Meng and Z Zhang ldquoSynthesis analysis and testingof BiOBr-Bi
2WO6photocatalytic heterojunction semiconduc-
torsrdquo International Journal of Photoenergy vol 2015 Article ID630476 12 pages 2015
[9] X Meng and Z Zhang ldquoFacile synthesis of BiOBrBi2WO6
heterojunction semiconductors with high visible-light-drivenphotocatalytic activityrdquo Journal of Photochemistry and Photobi-ology A Chemistry vol 310 pp 33ndash44 2015
[10] X Li R Huang Y Hu et al ldquoA templated method to Bi2WO6
hollow microspheres and their conversion to double-shellBi2O3Bi2WO6hollow microspheres with improved photocat-
alytic performancerdquo Inorganic Chemistry vol 51 no 11 pp6245ndash6250 2012
[11] M-S Gui W-D Zhang Y-Q Chang and Y-X Yu ldquoOne-step hydrothermal preparation strategy for nanostructuredWO3Bi2WO6heterojunction with high visible light photocat-
alytic activityrdquo Chemical Engineering Journal vol 197 pp 283ndash288 2012
[12] L C Courrol F R de Oliveira Silva and L Gomes ldquoAsimple method to synthesize silver nanoparticles by photo-reductionrdquo Colloids and Surfaces A Physicochemical and Engi-neering Aspects vol 305 no 1ndash3 pp 54ndash57 2007
[13] K S Knight ldquoThe crystal structure of russellite a re-determination using neutron powder diffraction of syntheticBi2WO6rdquoMineralogicalMagazine vol 56 no 384 pp 399ndash409
1992[14] Y Xu H Xu H Li J Xia C Liu and L Liu ldquoEnhanced
photocatalytic activity of new photocatalyst AgAgClZnOrdquoJournal of Alloys and Compounds vol 509 no 7 pp 3286ndash32922011
[15] G H He G L He A J Li et al ldquoSynthesis and visible lightphotocatalytic behavior ofWO
3(core)Bi
2WO6(shell)rdquo Journal
of Molecular Catalysis A Chemical vol 385 pp 106ndash111 2014[16] M Ge Y Li L Liu Z Zhou and W Chen ldquoBi
2O3minusBi2WO6
compositemicrospheres hydrothermal synthesis and photocat-alytic performancesrdquo The Journal of Physical Chemistry C vol115 no 13 pp 5220ndash5225 2011
[17] J Wielant T Hauffman O Blajiev R Hausbrand and HTerryn ldquoInfluence of the iron oxide acid-base properties on thechemisorption of model epoxy compounds studied by XPSrdquoJournal of Physical Chemistry C vol 111 no 35 pp 13177ndash131842007
[18] J Gamage McEvoy W Cui and Z Zhang ldquoSynthesis andcharacterization of AgAgCl-activated carbon composites forenhanced visible light photocatalysisrdquo Applied Catalysis BEnvironmental vol 144 pp 702ndash712 2014
[19] L Zhang W Wang Z Chen L Zhou H Xu and W ZhuldquoFabrication of flower-like Bi
2WO6superstructures as high
performance visible-light driven photocatalystsrdquo Journal ofMaterials Chemistry vol 17 no 24 pp 2526ndash2532 2007
[20] J Wu F Duan Y Zheng and Y Xie ldquoSynthesis of Bi2WO6
nanoplate-built hierarchical nest-like structures with visible-light-induced photocatalytic activityrdquo The Journal of PhysicalChemistry C vol 111 no 34 pp 12866ndash12871 2007
[21] L Zhang and Y Zhu ldquoA review of controllable synthesis andenhancement of performances of bismuth tungstate visible-light-driven photocatalystsrdquo Catalysis Science and Technologyvol 2 no 4 pp 694ndash706 2012
[22] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 Article ID 395502 2009
[23] W Xiong Q Zhao X Li and D Zhang ldquoOne-step synthesis offlower-like AgAgClBiOCl composite with enhanced visible-light photocatalytic activityrdquo Catalysis Communications vol 16no 1 pp 229ndash233 2011
[24] J-M Herrmann ldquoHeterogeneous photocatalysis fundamentalsand applications to the removal of various types of aqueouspollutantsrdquo Catalysis Today vol 53 no 1 pp 115ndash129 1999
[25] T Watanabe T Takizawa and K Honda ldquoPhotocataly-sis through excitation of adsorbates 1 Highly efficient N-deethylation of rhodamine B adsorbed to cadmium sulfiderdquoTheJournal of Physical Chemistry vol 81 no 19 pp 1845ndash1851 1977
[26] T Wu G Liu J Zhao H Hidaka and N Serpone ldquoPhotoas-sisted degradation of dye pollutants V Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO
2dispersionsrdquoThe Journal of Physical
Chemistry B vol 102 no 30 pp 5845ndash5851 1998[27] M R Hoffmann S T Martin W Choi and D W Bahnemann
ldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995
[28] T Xu L Zhang H Cheng and Y Zhu ldquoSignificantly enhancedphotocatalytic performance of ZnO via graphene hybridizationand the mechanism studyrdquo Applied Catalysis B Environmentalvol 101 no 3-4 pp 382ndash387 2011
[29] Y Zhang N Zhang Z-R Tang and Y-J Xu ldquoIdentification ofBi2WO6as a highly selective visible-light photocatalyst toward
oxidation of glycerol to dihydroxyacetone in waterrdquo ChemicalScience vol 4 no 4 pp 1820ndash1824 2013
[30] E T Yu J O McCaldin and T C McGill ldquoBand offsets insemiconductor heterojunctionsrdquo in Solid State Physics E Henryand T David Eds pp 1ndash146 Academic Press 1992
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of