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aDepartment of Chemistry, Anna University

Tamil Nadu, India. E-mail: jothivenkat@yabCentre for Nanoscience and Nanotechno

University, Tiruchirappalli-620 024, Tamil N

† Electronic supplementary informationzeolite-Y, UV-vis. Spectral changes of Rirradiation without any catalyst and %irradiation by different catalyst. See DOI:

Cite this: RSC Adv., 2014, 4, 21221

Received 17th February 2014Accepted 11th April 2014

DOI: 10.1039/c4ra01376j

www.rsc.org/advances

This journal is © The Royal Society of C

Facile synthesis of WO3 with reduced particle sizeon zeolite and enhanced photocatalytic activity†

K. Jothivenkatachalam,*a S. Prabhu,a A. Nithyaa and K. Jeganathanb

WO3 supported on zeolite-Y (WO3-ZY) was successfully synthesized by a facile impregnation method and

well characterized by various techniques. The photocatalytic activity of the prepared catalysts was

investigated for the degradation of Rhodamine B (RhB) under visible, UV and solar light irradiation. The

enhanced photocatalytic activity was observed for the catalyst WO3-ZY, which may be due to the

presence of more active sites that can adsorb a greater number of dye molecules. The TEM, FESEM and

adsorption studies confirm that the WO3 supported on zeolite-Y has a very small particle size of about

8 nm compared with the bare WO3 at 97 nm. The efficient electron–hole pair separation and the role of

active species were investigated by photoluminescence spectroscopy and the test of the effect of

scavengers, respectively. The mechanism for the photocatalytic degradation of RhB was proposed and

the pathway of RhB degradation was illustrated schematically.

Introduction

Semiconductor photocatalysis is a promising technique foraddressing environmental issues such as energy storage anddecontamination of environmental pollution.1 This techniqueprovides clean and recyclable hydrogen energy and also canutilize solar energy to decompose organic and inorganicpollutants present in air and aqueous media.2,3 TiO2 is the mostwidely used and best photocatalytic material; however, only asmall fraction of solar light (3–5%) can be utilized due to itswide band gap.4,5 Even though the visible light photocatalyticactivity of TiO2 has been reported in nitrogen-doped TiO2, thequantum efficiency of the nitrogen-doped TiO2 is much lowerthan that under UV light irradiation.6 In contrast, WO3 is n-typesemiconductor that has strong absorption in the solar spec-trum, stable physicochemical properties, and is resistant tophotocorrosion effects.7 The narrow band gap of about 2.4–2.8 eV and deeper valance band (+3.1 eV) results in additionaladvantages for visible light driven photocatalysis.7 However,due to fast recombination of electron–hole pairs and lowconduction band level, pure WO3 is not an efficient photo-catalyst.8 However, it has been found that the photocatalyticefficiency of the pure WO3 can be enhanced by several methods.Some examples are tuning a physical property such as

, BIT Campus, Tiruchirappalli-620 024,

hoo.com

logy, School of Physics, Bharathidasan

adu, India

(ESI) available: PXRD spectrum ofhB under visible, UV and solar lightdegradation of RhB under UV light10.1039/c4ra01376j

hemistry 2014

morphology and particle size,9–12 semiconductor coupling,13–16

noble metal deposition,7,14,15,17 and metal ion doping.18

Increasing the surface area and suppressing the electron–holepair recombination can also enhance the photocatalytic activityof WO3,8 but there are few reports available on tuning thephysical properties of WO3 to improve the efficiency undervisible light irradiation.19

Recently, researchers have intensively focused on meso-porous materials such as zeolite as a support for metal oxidesthat inuence photocatalytic activity through structural modi-cation.20–23 The zeolitic materials have gained signicantimportance due to their high surface area, thermal stability andtheir specic photophysical properties in charge and electrontransfer processes.24,25 The use of zeolite as a support for metaloxides improves the amount of photons absorbed by the cata-lyst and reduces the amount of metal oxides required.26 Despitethat there are several metal oxides supported on zeolitic mate-rials that proved to be better photocatalysts, there is no reporton WO3 supported on zeolitic materials for photocatalyticapplications.

For the rst time, we report a facile synthesis of WO3 sup-ported on zeolite-Y catalyst by impregnation method and itsphotocatalytic efficiency for the degradation of Rhodamine B(RhB) under visible, UV and solar light irradiation. Theprepared catalysts were well characterized by powder X-raydiffraction (PXRD), X-ray photoelectron spectroscopy (XPS),transmission electron microscopy (TEM), eld emission scan-ning electron microscope (FESEM), Raman, Fourier transforminfrared spectroscopy (FT-IR) and UV-vis diffuse reectancespectra (UV-DRS) techniques. Greatly enhanced photocatalyticactivity was observed in the catalyst WO3 loaded on zeolite-Y.The TEM, FESEM and adsorption studies conrmed the

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Fig. 1 PXRD pattern of the WO3 and WO3-ZY.

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reduced particle size of the catalyst. The efficient electron–holepair separation of the catalysts was investigated by photo-luminescence (PL) spectroscopic techniques. The photocatalyticactivity in the presence of different scavengers was demon-strated by testing which of the active species plays an importantrole in the degradation of the RhB. The mechanism for thephotocatalytic degradation of RhB is proposed; the pathway ofRhB degradation is also illustrated schematically.

ExperimentalMaterials

All analytical grade reagents of Na2WO4$2H2O, H2WO4, RhB,BaSO4 and zeolite-Y were used as such without further puri-cation. Deionized and double distilled water was usedthroughout this work.

Synthesis

The WO3-supported zeolite-Y (WO3-ZY) catalyst was prepared bythe facile impregnation method as follows. The zeolite-Y (1 g)was put into an aqueous medium and stirred. Aer that, 5 g ofH2WO4 was added into the above reaction mixture. Then, thereaction mixture was reuxed at 100 �C for 24 h. The obtainedprecipitate was collected by centrifugation, washed severaltimes using distilled water and dried. The dried sample wascalcinated at 500 �C for 3 h. For comparison, pure WO3 wasprepared by the precipitation method as reported in the litera-ture.27 The sodium tungstate was dissolved in distilled waterand slowly heated to 85 �C. The appropriate amount of warm,concentrated nitric acid was added drop-wise to this solutionwith vigorous stirring. The mixed solution was held at the sametemperature for 30 min under continuous stirring. The precip-itate was allowed to settle overnight at room temperature, thenwashed by adding a large amount of water and allowing theprecipitates to settle before decanting the liquid. Finally, theprecipitate was separated by centrifugation and dried. Aerdrying, the pure WO3 was calcined at 500 �C for 3 h.

Characterization

PXRD data were collected by a PAN analytical X'pert Pro dualgoniometer diffractometer. The data were collected with a stepsize of 0.008� and a scan rate of 0.5� min�1. The radiation usedwas Cu-Ka (1.5418 A) with a Ni lter, and the data collection wascarried out using a at holder in Bragg–Brentango geometry.XPS analysis was carried out by Kratos Axis-Ultra DLD instru-ment by passing 200 eV energy. During XPS analysis the samplewas irradiated with Mg Ka and the data collected at sweep ratesof 2 eV and 5 eV in a wide and narrow range scan, respectively.TEM analysis was done by JEOL model 2010 FasTEM instru-ment with a 200 kV accelerating voltage. An FESEM image wasobtained by a Carl Zeiss SIGMA instrument with 1.2 nm reso-lution. The energy-dispersive X-ray spectra (EDX) were recordedusing the INCAx-act Oxford Instrument equipped with SEM.Raman spectra were recorded by employing a Horiba JY Lab-RAMHR 800 Raman spectrometer coupled with a microscope inreectance mode with a 514 nm excitation laser source. UV-DRS

21222 | RSC Adv., 2014, 4, 21221–21229

spectra were recorded on Shimadzu UV-2450 UV-visible spec-trophotometer equipped with an integrated sphere assemblyusing BaSO4 as the reectance sample. FT-IR analysis was per-formed using Jasco FTIR 460 plus spectrophotometer. The PLspectrum was recorded by a JASCO FP-6500 spectrouorometerwith 300 nm excitation wavelength.

Photocatalytic test

The photocatalytic degradation of a model pollutant RhB waschosen to investigate the photocatalytic activity of the preparedcatalysts. In a typical experiment, 25 mg of the catalyst wassuspended in 50 mL of aqueous solution contains 10 mg L�1 ofRhB dye. Prior to irradiation, the suspension was held for30 min in the dark to achieve adsorption–desorption equilib-rium by aeration. Photocatalytic activity was investigated undervisible and UV light irradiation by 300W tungsten halogen lamp(8500 lumen) and 125 W medium pressure mercury lampemitting 365 nm (110 mW cm�2, measured by a Lutron UV lightMeter) light respectively. The reaction mixture was aeratedcontinuously under irradiation until the reaction mixture wasthorough mix. At the given time interval 3.5 mL of the samplewas withdrawn and centrifuged to separate the catalyst. Thedegradation of RhB was determined by measuring themaximum absorbance at 554 nm on a UV-visspectrophotometer.

Results and discussionCharacterization

Crystalline structure. The PXRD pattern of the preparedcatalysts is shown in Fig. 1. The peaks obtained in the patternare indexed with standard data (JCPDS no. 83-0950) and corre-spond to the monoclinic phase structure. In pure WO3, thepattern shows very sharp peaks that represent the high crys-tallinity and greater particle size. The diffraction peaksappeared in the WO3-ZY corresponds to WO3 indicating theformation of WO3 on the zeolite-Y (please see the ESI† for thePXRD pattern of pure zeolite-Y). On the other hand, there are nosharp peaks in the diffraction pattern of WO3-ZY that could be

This journal is © The Royal Society of Chemistry 2014

Fig. 3 EDX spectra of (a) WO ; and (b) WO -ZY.

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attributed to the smaller size particles of WO3. The crystallinesize of the WO3 and WO3-ZY in the (002) plane is calculated bythe Scherer formula to be around 43 and 26 nm, respectively.This result shows that the growth of WO3 on zeolite-Y is verylimited and controlled.

Morphology and particle size. The FESEM image of the WO3

sample shows spherical shaped particles with the average sizeof 102 nm, as shown in Fig. 2(a). The FESEM image of WO3-ZYshows very small particles (12 nm) as shown in Fig. 2(c). Sincethere are no distinct particles, it is difficult to obtain particlesize from the image. For comparison, the FESEM image ofzeolite-Y is shown in Fig. 2(b). The TEM image of WO3 is givenin Fig. 2(d), which further conrms the shape of the particles.The average particle size was calculated from the TEM image tobe around 97 nm, which is close to that calculated from FESEMimage. The highly magnied TEM image of WO3 is shown inFig. 2(e). The inter-planar distance from the TEM image wascalculated to be 0.39 nm, which is well matched with the latticespacing of (200) planes of the monoclinic WO3 structure. TheTEM image ofWO3-ZY shows that the particles are very small insize, as shown in Fig. 2(f); the particle size distribution is shownin the inset. The calculated average particle size ofWO3-ZY fromFig. 2(f) is around 8 nm. These FESEM and TEM results showsthat the WO3 particle size was reduced from 97 nm to 8 nmunder the given reaction conditions. This decrease in particlesize may provide more active sites. The elements present in the

Fig. 2 FESEM images of (a) WO3, (b) zeolite-Y, (c) WO3-ZY, (d and e); T

This journal is © The Royal Society of Chemistry 2014

catalysts WO3 and WO3-ZY were conrmed by the EDX analysisand are shown in Fig. 3(a and b).

XPS analysis. The elements and chemical states present inthe catalysts were further investigated by XPS analysis. Theoverview XPS spectra of the samples WO3 and WO3-ZY areshown in Fig. 4(a). The spectra clearly show the presence ofW4d, W4f and O1s peaks and the respective oxidation states ofthe elements are indexed. The narrow range spectra of W4d and

EM and HR TEM images of WO3; and (f) TEM image of WO3-ZY.

3 3

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Fig. 4 (a) XPS survey spectra of WO3 and WO3-ZY, and narrow rangesurvey spectra of (b) W4d, (c) O1s of WO3 and WO3-ZY.

Fig. 5 (a) Raman and (b) FT-IR spectra of WO3 and WO3-ZY.

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O1s corresponding to WO3 and WO3-ZY are shown in Fig. 4(band c). The binding energy observed at around 247 and 530 eVin Fig. 4(b and c) is ascribed to W4d and O1s of WO3, respec-tively. An obvious shi of W4d and O1s peaks in WO3-ZY to ahigher binding energy is observed in the spectra, which isattributed to the strong interaction between WO3 and zeolite-Y.The O1s peak shi from 530 eV to 538 eV is attributed to theoxygen of WO3 hydrogen bonded to the zeolite surface.28 On theother hand, the particle size variation and lattice variation canalso change the binding energy in XPS. The particle sizereduction will result in a higher binding energy shi, whichclearly shows the reduction of WO3 particle size in WO3-ZY.29

This reduction in particle size is in good agreement with resultsobtained from FESEM and TEM analysis.

Raman spectral analysis. The Raman spectra of the preparedcatalysts consist of three main regions, less than 200, 200–400and 600–900 cm�1, as shown in Fig. 5(a), which was wellmatched with the literature report of the monoclinic tungstenoxide phase.30,31 The Raman peaks at 135 and 184 cm�1 corre-spond to the (W2O2)n chains.30 The W–O–W bending modes ofbridging oxide ion peaks appear at 273 and 329 cm�1.30 Thepeaks at 720 and 809 cm�1 are attributable to the W–O–Wstretching mode in the tungsten oxide network.32 The intensityof the Raman peaks was very low for the catalystWO3-ZY, whichmay be due to the very small particle size.

FT-IR analysis. The FT-IR spectral characterization wascarried out to analyze the catalysts; the obtained spectra areshown in Fig. 5(b). The strong absorption peaks for pure WO3

21224 | RSC Adv., 2014, 4, 21221–21229

were observed in the 500–900 cm�1 range, which corresponds tothe n(O–W–O) stretching mode.33 The peak at around 750 cm�1

is attributable to the n(O–W–O) stretching mode.34 The bands inthe range of 3200–3550 cm�1 are ascribed to the n(O–H)stretching, and the band at 1625 cm�1 corresponds to the d(O–H) bending modes of the coordinated water.33

Optical properties. The optical properties of the catalystswere investigated by UV-vis DRS spectroscopy; results are shownin Fig. 6(a). The spectra reveal that all catalysts have absorptionedges above a wavelength of 400 nm. The band gap energies ofthe samples can be calculated by the following equation35,36

ahn ¼ A(hn � Eg)n/2 (1)

where a, n, Eg and A are the absorption coefficient, frequency ofthe light, band gap energy and a constant, respectively; and n isthe type of optical transition of a semiconductor, which is 1. Theband gap energy (Eg) of the catalysts can be calculated from theintercept of the tangent to the X axis from a plot of (ahn)1/2

versus energy (hn), as given in Fig. 6(b). The calculated band gapenergies of the samples are 2.52 and 2.73 eV for WO3 and WO3-ZY, respectively. The valance band (VB) edge potential of asemiconductor at the point of zero charge can be calculatedfrom the following equation37

EVB ¼ X � Ec + 0.5Eg (2)

where EVB is the VB edge potential; X is the electronegativity ofthe semiconductor; Ec is the energy of free electrons on thehydrogen scale (about 4.5 eV); and Eg is the band gap energy ofthe semiconductor. The conduction band (CB) edge potential

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Fig. 6 (a) UV-vis DRS and (b) plot of (ahn)1/2 vs. hn ofWO3 andWO3-ZY.

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(ECB) can be determined by ECB ¼ EVB � Eg. The X value for WO3

is about 6.60, and the calculated EVB and ECB of the catalysts are3.36 and 0.84 eV, respectively, for WO3 and 3.46 and 0.73 eV,respectively, forWO3-ZY. The band gap energy changes and blueshi in the UV-vis spectrum clearly suggest that the particle sizeof the catalyst has decreased.

Photocatalytic activity. The photocatalytic activity of theprepared catalysts for the degradation of RhB was demonstratedunder visible, UV and solar light irradiation. Before that, theblank experiment without any catalyst was carried out to test thestability of RhB under visible, UV and solar light irradiation.The UV-vis spectral changes of RhB under various light irradi-ations were recorded (see Fig. S1–S3 in the ESI†). There were nosignicant changes observed in the UV-vis spectrum, whichconrms the degradation of RhB is almost zero or negligibleunder the various light irradiations in the absence of any cata-lyst. These experimental results show RhB in aqueous mediumis highly stable under the given light irradiation. The percentdegradation of RhB was calculated by the following equation

%D ¼ (A0 � At)/A0 � 100 (3)

where %D is the percentage of degradation, and A0 and At areinitial absorption and absorption at time t, respectively.

Photocatalytic degradation of organic compounds usuallyfollows the pseudo-rst order kinetics model. The rate constantfor the degradation of RhB is calculated using the followingLangmuir–Hishelwood kinetic equation38,39

This journal is © The Royal Society of Chemistry 2014

ln(C0/C) ¼ kappt (4)

where C0 is the initial concentration of the dye solution(mol L�1); C is the concentration of the dye solution at time t(mol L�1); and kapp is the apparent rate constant (min�1).

The rate constant for the degradation of RhB was calculatedfrom the slope of the plot, ln(C0/C), vs. irradiation time.

Under visible light. The photocatalytic activity for thedegradation of RhB by the catalysts under visible light irradia-tion is shown in Fig. 7(a). The enhanced photocatalytic activitywas observed by the catalyst WO3-ZY, which may be due to highpercentage adsorption of dye on the surface of the catalyst. Thepercentage adsorption of RhB on the surface of the catalystunder dark aer 30 min is shown in the inset gure of Fig. 7(a).The high percentage adsorption of about 30% was achieved bythe catalyst WO3-ZY, whereas WO3 shows less than 10%adsorption. This high percentage of adsorption may be due todecreasing the particle size of WO3 on zeolite-Y, which mayprovide more active sites to adsorb dye molecules. This studyexperimentally conrms the reduced particle size of the catalystWO3-ZY. The photocatalytic activity of zeolite-Y catalyst for thedegradation of RhB is very minimum in visible light whencompared with WO3-ZY, as shown in Fig. 7(a).

Optimization study. To effectively utilize the catalyst in a lowamount and get high efficiency at an optimum dye concentra-tion, two sets of experiments were done. First, we changed theamount of WO3-ZY from 0.25 g L�1 to 1 g L�1 while keeping the10 mg L�1 dye concentration constant. Second, we changed thedye concentration from 5 mg L�1 to 20 mg L�1 while keeping0.5 g L�1 catalyst constant. The increased percentage degrada-tion of 58% to 92% was observed when the amount of thecatalyst was increased from 0.25 g L�1 to 0.5 g L�1, respectively.This may be due to the increased availability of active sites onthe catalyst surface, thereby increasing the available amount ofcatalyst. Upon further increasing the amount of catalyst, thedegradation efficiency does not increase, as shown in Fig. 7(b).This may be due to the aggregation of a large amount of catalyst,which causes a reduction in the number of active sites for theadsorption of dye molecules and photons. Moreover, a highconcentration of catalyst creates turbidity and thus reduces thepenetration intensity of light radiation by the scatteringeffect.40,41 As the dye concentration increases, the photocatalyticactivity decreases, as shown in Fig. 7(c). This may be due to adecreased number of photons reaching the surface of thecatalyst because more photons are absorbed by dye molecules.42

These experimental results suggest that the optimum reactioncondition to achieve better efficiency is 0.5 g L�1 catalyst and10 mg L�1 dye concentration.

Under UV and solar light. The photocatalytic efficiency of thecatalyst WO3-ZY was investigated under UV and solar lightirradiation. The photocatalytic degradation of about 86% wasobserved at 140 min under UV light irradiation, which is a veryhigh efficiency when compared withWO3 (see Fig. S4 in the ESI†for the degradation prole of different catalysts); this result isconsistent with that obtained under visible light irradiation.Under solar light irradiation, 95% degradation was observed at180 min. The rate constants for the degradation of RhB under

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Fig. 7 Percent degradation of RhB under visible light irradiation (a) over different catalysts, overWO3-ZY (b) on varying the amount of catalyst, (c)on varying the amount of RhB and (d) under different light irradiation.

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different light irradiations are given in Fig. 7(d). The rateconstant increased in the order visible < UV < solar light irra-diation. The high rate constant under solar irradiation sug-gested that the catalyst can be efficiently used for the conversionof solar energy.

Reaction mechanism and degradation pathway

Recombination of electron–hole pair. The photocatalyticefficiency of a catalyst can be enhanced by inhibiting therecombination of photo-generated electron–hole pairs. Thelower PL intensity of the catalyst can have a lower recombina-tion rate and a higher photocatalytic activity as the recombi-nation of electron–hole pair releases energy in the form ofuorescence.43,44 The PL spectra of the catalysts are shown inFig. 8(a). The PL intensity of the catalyst WO3-ZY shows thelowest intensity compared with pure WO3. It is suggested thatWO3-ZY has the lowest electron–hole pair recombination rate,which is consistent with the high photocatalytic activityobserved. This decrease in the PL intensity may be due to thesmall particle size of the catalyst, which can increase the surfacearea and thereby increase the interfacial charge–carriertransfer.19

Role of electron acceptors. Electron acceptors such as air andhydrogen peroxide can create more active radicals of cO2

� andcOH, respectively, which are strong enough to degrade organicmolecules. The experimental results for the photocatalytic

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degradation of RhB over WO3-ZY in the presence of air,hydrogen peroxide (5 mmol) and no acceptor under visible lightirradiation are shown in Fig. 8(b). The kapp of 0.0052 min�1 inthe absence of an electron acceptor increased to 0.0143 min�1

aer the addition of hydrogen peroxide. This enhanced photo-catalytic activity in the presence of electron acceptors may bedue to a decreased recombination rate of electron–hole pairsand formation of more active radicals.

Role of active species. The holes (h+) and radical trappingexperiments were carried out to investigate the role of reactivespecies in the photocatalytic degradation of RhB over WO3-ZYunder visible light irradiation. The changes of kapp for thedegradation of RhB in the presence of different scavengers (5mmol) are shown in Fig. 9(a). When t-BuOH (as the cOH scav-enger) was added,45 the kapp decreased slightly to 0.0035 min�1

from 0.0052 min�1. On the other hand, the kapp of RhB degra-dation decreased to 0.0023 min�1 when benzoquinone (BQ) wasadded as the cO2

� scavenger.46,47 However, upon the addition ofammonium oxalate (AO) as the h+ scavenger,48 the kappdecreased radically, to 0.0005 min�1. These decreases in thekapp upon the addition of different scavengers suggested that h+

and cO2� play a major role, whereas cOH is a minor active

species for the degradation of RhB. The active radical cO2� can

be formed by reacting photo-generated electrons with O2

molecules adsorbed on the surface of the catalyst,1 whichindicates that O2 is an efficient electron acceptor for generatingcO2

� and inhibiting electron–hole pair recombination.49,50

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Fig. 8 (a) PL spectrum of the catalysts and (b) effect of electronacceptor for the degradation of RhB.

Scheme 1 Proposed degradation pathway for the photocatalyticdegradation of RhB.

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Possible reaction mechanism and degradation pathway

Based on the effect of scavengers, a possible mechanism for thephotocatalytic degradation of RhB over WO3-ZY is illustrated inFig. 9(b). As shown in Fig. 9(b), the electron–hole pair is createdby the illumination of the catalyst. Then the photoinducedelectrons in the CB react with an O2 molecule adsorbed on thesurface of the catalyst and form cO2

� radicals to degrade RhB.Meanwhile, the photoinduced holes in the VB can directlydegrade RhB. The photocatalytic degradation of RhB can beillustrated as follows:

WO3 + hn / e�CB + h+VB (5)

Fig. 9 (a) Effect of different scavengers; (b) possible mechanism; and (c)degradation of RhB over WO3-ZY.

This journal is © The Royal Society of Chemistry 2014

e�CB + O2 / cO2� + catalyst (6)

RhB + cO2� / products (7)

RhB + h+VB / products (8)

It is well known that the degradation of RhB proceeds via twoprocesses of N-de-ethylation and destruction of the conjugatedstructure.51 The temporal UV-vis absorption spectral variationfor the photocatalytic degradation of RhB under solar lightirradiation is shown in Fig. 9(c). The absorption band at 554 nmhas decreased, which suggests the degradation of the xanthenering in RhB. The blue shi in the absorption spectrum isascribed to the formation of de-ethylated RhB.52 Based on theresults obtained from the UV-vis spectral changes, we proposethe degradation pathway of RhB schematically in Scheme 1: thedegradation of RhB occurred through de-ethlyation process,followed by the destruction of the conjugated xanthane struc-ture in RhB, which produces the benzenoid intermediates.53

the temporal UV-vis absorption spectral variation for the photocatalytic

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Aer that occurs, the schematic diagram shows the ringopening of the intermediates and mineralization process.

Conclusion

In this study, we have successfully synthesized and thoroughlycharacterized both pure WO3 and WO3 supported on zeolite-Y.The TEM, FESEM and adsorption studies conrm that thecatalyst WO3-ZY has a very small particle size: 8 nm. The pho-tocatalytic activity of the prepared catalysts was investigated forthe degradation of RhB under visible, UV and solar light irra-diation. The enhanced photocatalytic activity was observed forthe catalyst WO3-ZY. The higher photocatalytic activity of WO3-ZY under solar light irradiation compared with other lightirradiation sources suggests the catalyst can be utilized for solarenergy conversion. The efficient electron–hole pair separationof the catalyst provides the condition whereby enhanced pho-tocatalytic activity is obtained, as conrmed by PL spectra. Thetest of the effect of scavengers shows that the active species h+

and cO2� play a major role in the photocatalytic degradation of

RhB. The proposed mechanism for the photocatalysis anddegradation pathway of RhB is illustrated: it involves N-de-ethylation, destruction of conjugated structure, ring openingand mineralization processes.

Acknowledgements

The authors thank DST-SERC for nancial support, sanction no.SR\FT\CS-042\2008.

Notes and references

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