氧化铋光催化剂

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

SelectivepreparationofBi2O3visiblelight-drivenphotocatalystbydispersantand

calcination

LijunCheng,YongKang

SchoolofChemicalEngineeringandTechnology,TianjinUniversity,Tianjin300072,China

articleinfoabstract

Bi2O3visiblelightresponsivephotocatalystsweresynthesizedbychemicalprecipitationandconsequentcalcinationprocess.Theas-preparedsampleswerecharacterizedwithXRD,FESEM,UV–st,N-dopedb-Bi2O3withaveragelengthofabout252nmwasselectivelyfabricatedundertheoptimalpreparationconditionsobtainedbyinvestigatingin uenceofdispersanttype,dispersantdosage,calcinationtemper-atureandtimeonBi2O3crystallinephase,morphologyandotherperformances.Thephotocatalysthadstrongabsorptionforvisiblelightandef cientseparationofchargecarrier,whichmadeitagoodphoto-catalysttowardsdegradationofmalachitegreen.Approximately96.5%ofmalachitegreenwasdegradedafterilluminationfor300min.

Ó2013ElsevierB.V.Allrightsreserved.

Articlehistory:

Received2May2013

Receivedinrevisedform2August2013Accepted2August2013

Availableonline12August2013Keywords:Bi2O3

PhotocatalystN-dopedb-Bi2O3Dispersant

1.Introduction

Toutilizesolarenergyef ciently,developingnarrowbandgapvisiblelightresponsivephotocatalysthasattractedconsiderableinterestinphotocatalytic eld.

AmongvariousvisiblelightresponsivephotocatalystssuchasCdS[1,2],WO3[3,4]andFe2O3[5,6],Bi2O3hasbeenwidelyinves-tigatedforitssmallbandgapandstability[7–10].

Inrecentyears,considerablestudieshavefocusedonsynthesisofBi2O3photocatalystswithcontrollablemorphologiesbecauseofstrongrelationshipbetweentheirmorphologiesandtheirphotocatalyticactivities[11–13].Muruganandhametal.fabricatedbarlikebismuthoxalate(Bi2(C2O4)3Á7H2O)andmicrorod-likehy-dratedbismuthoxalate((BiOHC2O4)2ÁH2O)byhydrothermalpro-cesseswithdifferentsolventandobtainedvariousmorphologicala-Bi2O3bycalcinatingtheabovebismuthoxalatesatdifferenttemperature.PhotocatalyticdegradationofAcidOrange7(AO7)dyeindicatedthatthehoneycombbrushlikea-Bi2O3synthesizedbysinteringhydratedbismuthoxalateat300°Cwasthemostef -cient[11].TherearealsoreportsaboutcontrollablepreparationofBi2O3photocatalystsviaadjustingdispersantdosage[12,13].Forexample,Zhangetal.preparedgranularnanocrystalliteBi2O3inpresenceofpolyvinylpyrrolodone(PVP)surfactantandmicrosizedBi2O3rodswithoutPVP,degradationofmethylorange(MeO)showedthatthephotocatalystpreparedinpresenceofPVPhadbetterphotocatalyticactivitythanthatpreparedwithoutthesur-factant[12].Chenetal.fabricatedaseriesofBi2O3photocatalystsCorrespondingauthor.Tel.:+862227408813;fax:+862227403389.

E-mailaddress:ykang@(Y.Kang).

0925-8388/$-seefrontmatterÓ2013ElsevierB.V.Allrightsreserved./10.1016/j.jallcom.2013.08.010

underdifferentpHvaluesanddifferentdosesoflysinedispersantandstudiedeffectofthesesynthesisparametersonmorphologyoftheas-preparedsamples.Measurementofphotocatalyticactiv-itybydegradingRhBindicatedthatmesh-likenano akesBi2O3ob-tainedbyadding6mmollysineandadjustingpHto8.4showedthebestphotocatalyticactivity[13].WeiLiproposedasimplemethodtopreparesphericalmonodisperseBi2O3nanoparticlesinpresenceofpolyethyleneglycol(PEG4000)dispersantunderlowtemperatureanddiscussedin uenceofpreparationconditionssuchasconcentrationofBi(NO3)3anddispersant,reactiontemper-atureandtimeontheshapeandsizedistributionofBi2O3,butitsphotocatalyticactivitywasnotinvestigated[14].Therefore,toim-provethephotocatalyticperformanceofBi2O3bydispersantasamorphologymodi erandto rstproposeeffectofPEGonitsmor-phologyandotherperformancesrelatedtoitsphotocatalyticactiv-ity,PEGwithdifferentmolecularweight(PEG1000,4000,6000)wereusedasdispersanttoselectivelyprepareBi2O3withappropri-ateparticlesize.

Inadditiontomorphology,crystallinephaseofBi2O3iscloselyrelatedtoitsphotocatalyticactivityaswell.Huangetal.synthe-sizedamorphousb-Bi2O3nanoparticlesvialiquidphasemicrowavereactionandgraduallychangedtowellcrystallizedsheet-likenanoparticlesofb-Bi2O3bycalcinatingat300°Canda-Bi2O3at350°C.Thephotocatalyticactivityofb-Bi2O3fordegradationofRhBwasevidentlyhigherthanthatofa-Bi2O3[15].Qiuetal.pre-pareda-andb-Bi2O3nanowiresbyanoxidativemetalvapourtransportdepositiontechniqueandalsofoundthatb-Bi2O3nanowiresshowedhigherphotocatalyticactivitythana-Bi2O3nanowires[16].Ascrystallinephaseisdirectlydeterminedbycal-cinationtemperature,therelevantcalcinationparameterswere

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

86L.Cheng,Y.Kang/alsostudiedtorealizeselectivesynthesisofBi2O3with

crystallinephase.

Inthiswork,Bi2O3sampleswerefabricatedbyitationtechnique,followedbyconsequentChangesofmorphologyandotherperformancesdispersantandcalcinationparameterswereN-dopedb-Bi2O3wasselectivelyobtainedunderthearationconditions,whichwasalmostthe rsttimeviaAsisknown,dopingofTiO2withnitrogencouldgapandincreaseitsabsorptionforvisiblelight[17],ofBi2O3withnitrogenisrarelyreported,whichanewinsightforcontrollablepreparationofBi2O3performances.

2.Experimentaldetails2.1.SynthesisofBi2O3

AllthechemicalreagentsusedinthisworkareA.R.grade.Bi2O3powderwaspreparedaccordingtothefollowingprocess.Firstly,9.7gBi(NO3)3Á5H2Owasdis-solvedin100mLHNO3(v(HNO3):v(H2O)=1:9)andcertainamount(theinitialdos-agewas1g)ofdispersant(PEG1000,4000or6000)wasaddedintothesolution.Secondly,thesolutionwasadded0.5mol/LofNaOHsolutionwhichwaspreparedbydissolving10gNaOHin500mLdeionizedwaterdropbydropunderstirring.Afterreactingfor2h,thewhiteprecipitatewasseparatedbycentrifugation,washedwithdeionizedwaterandethanolfor vetimes,respectively,driedinanelectricthermostaticdryingovenat80°Candcalcinatedinamuf efurnaceatcer-taintemperature(theinitialtemperaturewas400°C)forcertaintime(theinitialtimewas2h).2.2.Characterization

ThecrystallinephaseofallthesampleswereinvestigatedbyX-raydiffractionanalysis(XRD)onaD/MAX-2500unitwithCuKaradiation(k=1.54056°A).ThesamplemorphologieswererecordedbyFieldEmissionScanningElectronMicro-scope(FESEM)onaNanosem430unit.UV–Visdiffusere ectionspectraofthephotocatalystsweremeasuredonaLambda750SUV/VISSpectrometer.Photolumi-nescencespectra(PL)wereobtainedonaJobinYvonFluorolog3-21 uorescencespectroscopy.AndtheabsorbanceofmalachitegreensolutionwasobtainedonaUV7500UltravioletVisibleSpectrophotometer.2.3.Photocatalyticexperiments

Malachitegreenwasusedasthetargetpollutant.Theexperimentswerecarriedoutaccordingtothefollowingprocess.50.0mgofphotocatalystwasdispersedin100mLmalachitegreensolutionwithconcentrationof10mg/Lin300mLbeaker.Beforeillumination,thesuspensionwasmagneticallystirredinthedarkfor1htoestablishadsorption–desorptionequilibriumofmalachitegreenonthephotocat-alystsurface.Thenthesuspensionwasirradiatedundera200W lamentlamp,whichwaspositionedasideabout5cmawayfromthebeaker.Theabsorbanceofthesolution(centrifugalizedtoseparatethedispersedphotocatalystbeforetesting)wasdetectedevery30min.TheinitialconcentrationandabsorbanceofthesolutionweredenotedbyC0andA0,respectively.Accordingtothelinearrelationshipbe-tweenconcentrationandabsorbance(C/C0=A/A0),theconcentrationofmalachitegreensolutionatdifferenttimecouldbecalculated.

3.Resultsanddiscussion

3.1.EffectofPEGwithdifferentmolecularweight

PEGactsasashapedirectorwhenusedasdispersanttoprepareBi2O3becauseitcanbeabsorbedonthecrystalsurfacesofparticlestoformalayerofmembranetoreduceinterparticleforceandpre-ventparticlesfromdirectcollision,whichmakesparticlesnoteas-ilyaggregate[14].

Inthispaper,PEG1000,4000and6000wereusedasdispersanttofabricateBi2O3,respectively.Thedispersantdosagewas1.0g,thecalcinationtemperature400°Candthecalcinationtime2h.Fig.1showstheXRDpatternsofallthepreparedBi2O3samples.Itisclearthatwhateverdispersantwasused,allthediffractionpeaksofthesamplewereconsistentwithJCPDScardNo.41-1449,implyingpuremonoclinicphaseBi2O3(a-Bi2O3)wassynthesized.

Thecorrespondinglatticeconstantswere:a=5.850Å,b=8.170Å,c=7.512Å.Thesharppeaksindicatedthatallthesam-pleswerehighlycrystallized.Besides,accordingtotherelationshipbetweenintensityofthestrongestpeak,whichindicated(120)crystalface,withotherpeaks,itcouldbefoundthatthe(120)crystalfaceofBi2O3synthesizedbyPEG4000grewthemostpref-erentially,thesecondwasthatofBi2O3synthesizedbyPEG6000andthelastwasthatofBi2O3synthesizedbyPEG1000.

Thesamples’morphologieswereobservedbyFESEM,asshowninFig.2.ItisevidentthatBi2O3particleswerepeanut-likeforallsamples.TheparticlesizeforPEG1000wasrelativelyuniform,inotherword,thesizedistributionrangewasrelativelynarrow,aboutlengthof428–762nmandwidthof214–333nm.Thiscanbeexplainedasfollows.TheconcentrationofPEG1000wasthelargestunderthesamedispersantdosage,somoreparticlescouldbeenwrappedtoavoidforminglargeclusterscomparedtoPEG4000and6000,resultinginsmallerparticlesizeandmoreuniformsizedistribution.Besides,theBi2O3particlesobtainedusingPEG1000asdispersantweremoreinclinedtoisotropicgrowth(asdis-cussedinXRDpatternssection),whichmadetheirlength–widthratioswerethesmallest.However,ifPEG4000wasused,the(120)crystalfaceofBi2O3particlesgrewthemostpreferentially,thusleadingtotheirlength–widthratioswerethelargest.Inaddi-tion,theconcentrationofPEG4000wasjustaquarterofPEG1000,somultipleparticlesmaybeabsorbedonthesamePEG4000molecularchainandeasilyformedclusters,whichcausedseriousparticleagglomeration.Therefore,theparticlesizewasnon-uni-formandthesizedistributionwaswide.Accordingtostatistics,thelengthrangeofBi2O3particleswasabout285–1409nmandthewidthrange190–371nmforPEG4000,whichmaygiverisetoitssmallestspeci csurfacearea(1.375m2/g,whilethespeci csurfaceareaforPEG1000and6000were1.586m2/gand1.381m2/g,respectively).WhenPEG6000wasused,althoughitsconcentra-tionwasevensmallerthanPEG4000andmultipleparticleswerealsoinclinedtobeabsorbedonthesamePEG6000molecularchain,itslongerchainprobablycurveandtwinetoenwrapparti-cles,whichplayedroleofsterichindrancemoreef cientlythanPEG4000.Besides,thepreferentialgrowthof(120)crystalfaceforPEG6000wasrelieved,implyingthelength–widthratiosofBi2O3particlesweresmallerthanthatofPEG4000,sotheoverallsizedistributionwasrelativelynarrowerthanPEG4000.Bymea-surement,thelengthrangewasabout476–952nmandthewidthrangewas238–357nm.Throughtheabovediscussion,itcouldbeconcludedthatthesizeofBi2O3particlesobtainedbyPEG1000wasthesmallest,whichcontributedtotheirseriousagglomerationinthesubsequentcalcinationprocess,asseeninFig.2(a).

TheUV–Visdiffusere ectionspectraofBi2O3samplesobtainedbydifferentdispersantwerealsomeasured,asshowninFig.3(a).It

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

couldbeseennomatterwhatdispersantwasused,thesampleshowedalmostthesamelightabsorptionperformancewiththeothertwo.WhenPEG1000wasused,Bi2O3hadthelargestabsorp-tioninultravioletregion,whileitsabsorptionforvisiblelightwasalittleweakerthanthatofBi2O3synthesizedbyPEG4000andPEG6000.Besides,Bi2O3preparedbyPEG6000showedstronger

(Ahm)2versusphotoenergy(hm)wereabout2.91eV,2.906eVand2.89eVforPEG1000,4000and6000,asshowninFig.3(b).

Tocomparephotocatalyticactivitiesofallthethreesamples,malachitegreensolutionwasusedasthemodelpollutant.Itscon-centrationchangewithirradiationtimeisshowninFig.4.Ingen-eral,Bi2O3preparedbyPEG1000demonstratedthehighestphotocatalyticactivityformalachitegreenalthoughthedifference

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

88L.Cheng,Y.Kangamongallthethreesamplesbecameverysmallwhen

st,approximatelychitegreenwasdegradedforPEG1000.ThebestactivityofBi2O3obtainedbyPEG1000wascloselysmallestgrainsizeamongallthesamples.ForPEG6000,theirdegradationratesformalachitegreenand94%,respectively.Fromtheabovediscussion,itducedthatBi2O3synthesizedbyPEG6000hadandmoreabsorptionforlightthanthatsynthesizedsotheformershowedbetteractivity.Besides,thementwasalsocarriedouttoindentifytheroleplayed.Itisclearthattheconcentrationofmalachiteoutphotocatalystdecreasedapproximately14%afterfor300min.

Tomaketheaboveresultsmoreclear,theparticletionedge,bandgapenergyanddegradationrateofallobtainedbyPEGwithdifferentmolecularweightTable1.

3.2.Effectofdispersantdosage

DispersantdosageisalsoanimportantfactorwhichcanaffectmorphologyofBi2O3.Ifthedispersantdosageistoosmall,thedis-persantcannoteffectivelyproducesterichindranceandevenab-sorbmultipleparticlesonitsmolecularchaintoprovidepossibilityforparticleagglomeration.Ifthedispersantdosageistoolarge,sterichindrancewillbeweakenedassomedispersantmolecularchainstwinewitheachother,thuscausinginterparticleresistancebecomeweakandsomegrainsaggregatetogethertoformlargeparticles.Therefore,dispersantdosageshouldbeappro-priatelycontrolled.

Inthispaper,1g,2gand3gPEG1000wereusedasdispersanttofabricateBi2O3,respectively.Thecalcinationtemperaturewas400°Candthecalcinationtimewas2h.TheXRDpatternsofallthesamplesareshowninFig.5.BycomparingwithPDF(PowderDiffractionFile)cards,itisfoundthatallthecharacteristicpeakswerecorrespondingtoJCPDSNo.41-1449,sopurea-Bi2O3wasob-tained.Thesharppeaksindicatedthatallthesampleswerewellcrystallized.

Themorphologiesofthesamplespreparedbyadding2gand3gofPEG1000areseeninFig.6.TheBi2O3particlesagglomeratedseriouslyaftercalcinationwhenthedosageofPEG1000was2g,whiletheagglomerationsituationimprovedalittlewhenthedis-persantdosagewas3g.Accordingtostatisticmeasurement,thelengthrangewasabout476–667nmandthewidthrangewas190–285nmforBi2O3synthesizedby2gofPEG1000.AndforBi2O3synthesizedby3gofPEG1000,thelengthrangeandwidthrangewereabout666–1048nmand214–323nm,respectively.WhenthedosageofPEG1000increasedfrom1gto2g,itfurtherenwrappedparticlestopreventparticlesfromagglomerationeffec-tively.Butifthedispersantdosageincreasedupto3g,whenthedispersantconcentrationexceededtheoptimalvalue,somedisper-santmolecularchainstwinedwitheachotherandsterichindrancewasweakened,leadingtosomeparticlesaggregatedtogether.SotheappropriatedosageofPEG1000inthisworkwas2g.

Fig.7(a)showsthelightabsorptionperformanceofBi2O3fabri-catedbydifferentdosageofPEG1000.Itcanbeclearlyseentheabsorptionabilitiesofthesampleswerealmostthesameinvisibleregion.Accordingtoextrapolationprinciple,theabsorptionedgeoftheas-preparedBi2O3whenPEG1000dosagewas1gor3glo-catedatabout439nm,whiletheabsorptionedgeshiftedtowardsalittlelongerwavelength,about443nmwhenPEG1000was2g.Accordingly,thebandgapenergyfor1gor3gwas2.91eVandthatfor2gwas2.89eV,asseeninFig.7(b).

Thethreesamples’photocatalyticactivitieswerealsomeasuredbydegradingmalachitegreensolution.TheconcentrationchangeofmalachitegreenwithirradiationtimeisshowninFig.8.Appar-ently,whenthedosageofPEG1000was2g,theobtainedBi2O3showedthebestphotocatalyticactivitytowardsdegradationofmalachitegreen.Thedifferenceofthreesampleswasremarkableat rst150min,buttendedtobecomeverysmallafterthat.Afterilluminationfor300min,approximately95.45%ofmalachitegreenwasdegraded.Whilethedegradationrateswhen1gand3gofPEG1000wereusedwerejust94.06%and92.07%,respectively.Thismaybebecausetheparticlesizewassmaller,theabsorptionforvisiblelightwasstrongerforBi2O3synthesizedby2gofPEG1000.Theparticlesize,absorptionedge,bandgapenergyanddegra-dationrateofthesamplessynthesizedbydifferentdosageofPEG1000arealsosummarized,asseeninTable2.3.3.Effectofcalcinationtemperature

Calcinationtemperaturedeterminesphotocatalyst’scrystallinephase,whichprobablyaffectsphotocatalyst’sactivitygreatly.TorealizecontrollablepreparationofBi2O3withappropriatecrystal-linephase,in uenceofcalcinationtemperatureonperformancesofBi2O3wasstudied.

TheXRDpatternsofthesamplesobtainedunderdifferenttem-perature(300°C,350°Cand400°C)areshowninFig.9.Whenthecalcinationtemperaturewas300°Cor350°C,the nalproductwasmixtureoftetragonalBi2O3(b-Bi2O3,JCPDSNo.27-0050)andorthorhomibcBi5O7NO3(JCPDSNo.51-0525),indicatingthat

Table1

Particlesize,absorptionedge,bandgapenergyanddegradationrateofthesamplesobtainedbyPEGwithdifferentmolecularweight.

ParticlesizeWidth(nm)

PEG1000PEG4000PEG6000

214–333190–371238–357

Length(nm)428–762285–1409476–952

439440445

2.912.9062.89

94.0693.2794

Absorptionedge(nm)

Bandgapenergy(eV)

Degradationrate(%)

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

ticlesizewasinclinedtobecomelargerwithincreaseofsinteringtemperature.

Fig.11showsUV–Visdiffusere ectionspectraofBi2O3sinteredatdifferenttemperature.Whenthetemperaturewas350°C,theobtainedsampleshowedthestrongestabsorptionnomatterinultravioletregionorinvisibleregionamongallthesamples.Whenthetemperaturewasjust300°C,thephotocatalyst’sabsorptionforlightwassmallerthanthatcalcinatedat350°C.Therefore,itcanbeconcludedthatwithcalcinationtemperatureraisingandBi5O7NO3graduallytransformingtob-Bi2O3,theabsorptionabilityofN-dopedb-Bi2O3forvisiblelightalsoincreased.Butifthetemper-atureraisedto400°C,whenN-dopedb-Bi2O3completelychanged

Table2

Particlesize,absorptionedge,bandgapenergyanddegradationrateofthesamplesobtainedbydifferentdosageofPEG1000.

ParticlesizeAbsorptionBandgapDegradationWidth(nm)Length(nm)edge(nm)energy(eV)rate(%)1g214–333428–7624392.9194.062g190–285476–6674432.8995.453g

214–323

666–1048

439

2.91

92.07

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

topurea-Bi2O3,theabsorptionofa-Bi2O3forultravioletlightwasstrongerthanN-dopedb-Bi2O3synthesizedbycalcinationat300°C,butinvisibleregion,N-dopedb-Bi2O3hadstrongerabsorp-tionthana-Bi2O3.Accordingtoextrapolationprinciple,theabsorp-tionedgesoftheas-preparedBi2O3locatedat535nm,533nmand443nmfortemperatureof350°C,300°Cand400°C,respectively.

seenwhenthecalcinationtemperaturewas350°C,thephotolumi-nescenceintensitywasthelowestamongallthephotocatalysts.Whenthetemperaturewasjust300°C,theintensitywasthehighest.Andtheintensityfellinbetweenwhenthecalcinationtemperatureincreasedto400°C.Therefore,electron–holepairsintheN-dopedb-Bi2O3fabricatedat350°Cshowedthemosteffec-tiveseparation.

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

Fig.13showsphotocatlysts’activitiesfordegradingmalachitegreen.Obviously,theN-dopedb-Bi2O3fabricatedat350°Cdemon-stratedthehighestactivity.Afterilluminationfor300min,about96%ofmalachitegreenwasdegraded.WhiletheN-dopedb-Bi2O3fabricatedat300°Chadthelowestactivity.Only70%ofmal-achitegreenwasdegradedafter300min.Fora-Bi2O3obtainedat400°C,itsphotocatalyticactivitywasapparentlylowerthanthatobtainedat350°Cbefore240min,butdifferencebetweenthetwosamplesbecamequitesmallafter240min,andlast,approxi-mately95.45%ofmalachitegreenwasdegradedbya-Bi2O3.Fromthepreviousdiscussion,theN-dopedb-Bi2O3fabricatedat350°Chadrelativelysmallparticlesize,smallestbandgapandthemosteffectiveseparationofelectron–holepairs,soitsactivitywasrelativelyhigher.Besides,althoughtheparticlesizeofN-dopedb-Bi2O3fabricatedat300°Cwassmallerthana-Bi2O3obtainedat400°Canditsbandgapwassmalleraswell,itscrystallinitysitua-tionwasworsethana-Bi2O3andphotoluminescenceintensitywashigher,whichmayleadtoitslowerphotocatalyticactivity.Fromthefollowingcurve,itcanbeseenafter210min,theactivityof

3.4.Effectofcalcinationtime

Intheabovesection,N-dopedb-Bi2O3waspreparedwhentheprecursorwascalcinatedat350°Cfor2h.Tolearnaboutthecon-tentchangeofBi2O3andBi5O7NO3withcalcinationtimeandchangeofotherperformances,experimentswereconductedunderdifferentcalcinationtime.

Fig.14showstheXRDpatternsofthephotocatalystssubjectedtodifferentcalcinationtime.Withcalcinationtimelengthening,thepeaksfromBi5O7NO3becameweakerandthepeaksfromb-Bi2O3becamestronger,indicatingBi5O7NO3graduallychangedtob-Bi2O3.Eventhecalcinationtimeprolongedto6h,the nalprod-uctwasstillN-dopedb-Bi2O3.

Themorphologiesofthesamplessinteredfor4hand6hareshownasfollows.Whenthecalcinationtimewas2h,theaveragesizeofN-dopedb-Bi2O3wasabout200nm(Fig.10(a)).Whenthetimeprolongedto4hand6h,theaverageparticlesizeincreasedtoabout252nmand260nm,respectively.Itisclearthatthe

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

growthrateofN-dopedb-Bi2O3particlesfrom2hto4hwaslargerthanthatfrom4hto6h(seeFig.15).

Fig.16showsUV–Visdiffusere ectionspectraofthethreeN-dopedb-Bi2O3samples.Theabsorptiondifferenceofthesampleswasquitesmall.Basedonextrapolationprinciple,theabsorptionedgeofN-dopedb-Bi2O3subjectedto6hlocatedat533nm,andthecorrespondingbandgapwas2.45eV.Whentheprecursorwascalcinatedfor4h,theabsorptionedgeshiftedtowards536nmandthebandgapreducedto2.43eV.Whiletheabsorptionedgeandbandgapfor2hwere535nmand2.44eV,respectively(Fig.11).Therefore,whenthecalcinationtimewas4h,the

4.Conclusions

AnewinsightforselectivepreparationofBi2O3photocatalystwithappropriateparticlesizeandcrystallinephasebyusingPEGdispersantandadjustingcalcinationparameterswasproposed.Byinvestigatingin uenceofpreparationconditionsonBi2O3crys-tallinephase,morphologyandotherperformances,N-dopedb-Bi2O3withbestphotocatalyticactivityformalachitegreenwasselectivelyobtainedbyusing2gofPEG1000asdispersantandcal-cinationat350°Cfor4h.Afterilluminationby200W lamentlampfor300min,approximately96.5%ofmalachitegreenwaseliminated.

Selective preparation of Bi2O3 visible light-driven photocatalyst by dispersant and calcination

L.Cheng,Y.Kang/JournalofAlloysandCompounds585(2014)85–9393

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