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