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(%)