Photodegradation of methyl orange with PANImodified BiOCl photocatalyst under visible light irradia.docx

Photodegradation of methyl orange with PANImodified BiOCl photocatalyst under visible light irradia.docx

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PhotodegradationofmethylorangewithPANImodifiedBiOClphotocatalystundervisiblelightirradia

PhotodegradationofmethylorangewithPANI-modifiedBiOCl

photocatalystundervisiblelightirradiation

QizhaoWanga,b*,JuanHuia,JiajiaLia,YuxiaCaia,ShuqunYina,FangpingWanga,*,BitaoSua

aCollegeofChemistryandChemicalEngineering,NorthwestNormalUniversity,Lanzhou730070,China

bKeyLaboratoryofEco-Environment-RelatedPolymerMaterials,MinistryofEducationofChina,KeyLaboratoryofGansuPolymerMaterials,Lanzhou730070,China

*Correspondingauthor.Tel:

+869317972677;Fax:

+869317975521.

E-mailaddresses:

wangqizhao@;qizhaosjtu@（Q.Wang）

wangfplz@（F.Wang）

ABSTRACT

PhotocatalystBiOClmodifiedbypolyaniline（PANI/BiOCl）wassynthesizedviaafacilechemisorptionsmethod.X-raydiffraction（XRD）,Scanningelectronmicroscopy（SEM）andUV-visdiffusereflectancespectroscopy（DRS）wereemployedtostudythephasestructure,morphologyandopticalpropertiesofthesamples.TheresultsshowedthatthePANIincreasedabsorptionintensityandabsorptionbandsofthepureBiOCl.Photodegradationofmethylorange（MO）onthesampleswereinvestigatedundervisiblelightirradiationand7wt%PANI/BiOClcompositeshowedthehighestphotocatalyticactivity.TheenhancedphotocatalyticperformancecouldbeattributedtoPANI/BiOClcompositesandthesynergisticeffectbetweenPANIandBiOCl.Accordingtoexperimentalresults,thepossiblephotocatalyticmechanismofthePANI/BiOClphotocatalystswasproposed.

Keywords:

PANI/BiOCl;Photocatalysis;Synergisticeffect;photodegradation

1.Introduction

SinceFujishimaandHondareportedTiO2photochemicalelectrodeforsplittingwaterin1972[1],thestudyonthedevelopmentofphotocatalystsusedfortheremovalofenvironmentalpollutantsandtheutilizationofsolarenergyhasattractedincreasingattention[2].Duringthelasttwodecades,besidesthefocusedworkonTiO2modifications,manyeffortsweremadetodevelopothernovelefficientphotocatalysts.Thereportedphotocatalystsystems,tothebestofourknowledge,canbegenerallyclassifiedasoxides[3],sulfides[4],oxysulfides[5],nitrides[6]andoxynitride[7].Recently,Bi-basedoxychlorides（BiOCl）havedrawnmuchattentionfortheirpotentialapplicationinthetreatmentofcontaminantsinwaterandenvironmental[8-9].BiOClwithawidebandgap（3.19-3.60eV）canonlyabsorbultravioletlight,whichismerelyabout3%ofthesolarenergyspectrum[10-12].TheintrinsicpropertyofBiOCllimitsitsefficientutilizationofsolarenergyaswellasphotocatalyticactivity.InordertoextendthephotoresponseofBiOCltothevisibleregion,manymodificationapproacheshavebeenproposed,suchasmetaldoping（Mn/BiOCl[13]）.ButmanyattemptshavebeenadoptedtoenhanceitsactivitybymodifyingBiOClwithothersemiconductorsthatcanabsorbvisiblelight,suchas,Ag/AgCl/BiOCl[14],Ag/AgX/BiOX[15],WO3/BiOCl[16],Fe3O4/BiOCl[17],Bi2S3/BiOCl[18],Bi2O3/BiOCl[19],BiOCl/BiOI[20]andBiOI/BiOCl[21].

Recently,theconjugatedpolymerswithextendingπ-conjugatedelectronsystemssuchaspolyaniline,polypyrrole,polythiopheneandtheirderivativeshaveshowngreatpromisingduetotheirwideabsorptionregioninthevisiblelightrange,highmobilityofchargecarriersandexcellentstability[22].Furthermore,comparedwithdopednoblemetal,PANIisrelativelycheapandeasilysynthesized.SomestudieshavebeenpublishedonthecombinationofconductivepolymerandTiO2toimprovetheirphotocatalyticperformanceofUVandvisiblelight[23-26].

Inourpresentwork,thenovelphotocatalystsaredevelopedbetweenBiOClandPANItomakeefficientuseofvisiblelight.PureBiOClandPANIshowedverylowphotocatalyticactivityundervisiblelight,theirnanocompositesinduceddecompositionofmethylorange（MO）.ThemechanismwithPANI/BiOClphotocatalystshasbeenproposed.BothPANI/BiOClcouldabsorbvisiblelightandthesynergisticeffectremarkablyenhancedphotocatalyticactivity.

2.Experimental

2.1PreparationofthePANInanoparticle

Allreagents（SinopharmChemicalReagentCo.,Ltd）wereofanalyticgradeandusedwithoutfurthertreatment.5.705gofammoniumperoxydisulfatewasdissolvedinto50mLofwaterandwasaddedinto2.328gofanilinemonomerbythedropwise,whichconstantlystirringatlowtemperature.Thepolymerizationwasallowedtoproceedfor24handthegreenish-blackprecipitatedofpolyanilinewasobtained.Theprecipitateswerecentrifuged,andthenwashedwithdistilledwaterandethanol.Theresultingpolyanilinewasfinallydriedundervacuumovenfor12hat60℃.

2.2PreparationoftheBiOClsample

BiOClpowderwassynthesizedbyahydrolysismethod.Bi2O3wasdissolvedinexcessiveconcentratedhydrochloricacidtoreceiveatransparentBiCl3-HClaqueous.WhenthepHvalueofthesolutionwasadjustedbetween2and3withammonia,thewhitecolloidappeared.Afterthecolloidwasheatedat40℃forhalfanhour,apowderyBiOClmaterialconsistingofsmallplate-likecrystalswasobtained.Theprecipitateswerewashedseveraltimeswithwaterandethanoluntilnochloridionwasleftinthesolution,andthendriedat60℃inovenfor6hbeforefurthercharacterization[27].

2.3PreparationofthePANI/BiOClphtocatalysts

ThePANI/BiOClphotocatalystswerepreparedasfollows:

PANIwasdispersedintetrahydrofuran（THF）toobtainaconcentrationof0.45g/L-1solution,andanamountofBiOClpowderwasaddedto100mLoftheabovesolutionandthenstirredfor24h.Theprecipitatewascentrifugedandwashedseveraltimesbydistilledwaterandethanol,andthentransferredtooventodryat80°Cfor6h.Accordingtothismethod,differentweightratiosofPANI/BiOClphotocatalystsfrom1wt%to9wt%weresynthesized.

2.4Characterizationofthephtocatalysts

X-raydiffractionpatterns（XRD）ofthesamplespreparedwererecordedonaRigakuX-raydiffractometerD/MAX-2200/PCequippedwithCuKαradiation（40kV,20mA）.ThestructuralinformationofthesampleswasmeasuredbyFouriertransformspectrophotometer（FT-IR,Vertex70,Bruker）withKBrasthereferencesample.ThesurfacemorphologyofproductswasobservedusingJSM-6701Ffieldemissionscanningelectronmicroscope（FE-SEM）.UV-visibleDiffuseReflectancespectroscopy（DRS）ofpowdersampleswascarriedoutatroomtemperatureusingaShimadzuModel2550UV-visiblespectrophotometeroverawavelengthrangeof200-800nm.ThereflectancespectraweretransformedtoabsorptionintensitybyusingKubelka-Munkmethod.Thephotoluminescence（PL）spectraweremeasuredatroomtemperatureunder390nmexcitationwavelength（PE,LS-55）.

2.5Measurementofphotocatalyticactivity

Thephotocatalyticactivitiesofthesampleswereevaluatedbythedegradationofmethylorange（MO）inasinglecompartmentphotoreactor.Photocatalyticreactionwaspreformedinaquartztubereactor.0.05gofPANI/BiOClphotocatalystswereplacedintheaqueoussolutionofMO（50mL,10mg/L）.Ahighpressurexenonshortarclamp（CHF-XM35-500W,BeijingChangtuoCo.）wasservedasthevisiblelightsource,aglassfilter（ZUL0400,AsahiSpectraCo.）wasaddedtoallowvisiblelight（λ>420nm）topassthrough.Thesuspensionswerestirredfor1htoreachadsorption-desorptionequilibriumofMOmoleculesonthesurfaceofcatalyst.Duringthephotoreaction,about4mLofsuspensionwascollectedatgiventimeintervalsandcentrifugedtoremovetheparticles.TheconcentrationofMOwasdeterminedbyrecordingthevariationsofsupernatantat464nmusingUV-visspectrophotometer（TU–1901,BeijingPgeneral）.

3.ResultsandDiscussion

3.1.Crystalstructureandmorphology

Fig.1showstheXRDpatternsoftheBiOClandPANI/BiOClphotocatalysts.ThehydrolysissynthesizedBiOClwascrystallizedintoastandardtetragonalstructure（JCPDS06-0249）.Themaindiffractionpeakpositionsoftheobtainedproductsappearat11.98º,24.10ºand33.45º,whichcorrespondtothe（001）,（101）and（102）crystalfacesofBiOCl,respectively.ThecrystallatticeparametersofBiOClwerecalculatedtobea=b=0.3891Å，c=0.7369Å,whichwereconsistentwithliterature[27].TheXRDpatternsofPANI/BiOClphotocatalystshardlychangedinpeakpositionsandshapescomparedwiththeBiOCl,indicatingthatthemodificationwithPANIdidnotinfluencethelatticestructureofBiOCl.Inaddition,thepeakintensitiesoftheBiOCldecreasedgraduallyuponenhancingthePANIcontents,soitcouldbeascribedtothedecreasedparticlesizeandincreaseddispersityoftheBiOClnanoparticles.

Fig.2showstheSEMimagesoftheas-preparedPANI,BiOCland7wt%PANI/BiOClrespectively.AsshowninFig.2A,theSEMimageofPANIrevealedthattheas-preparedsamplesconsistedofamorphousparticlesandthediameterofthemicrosphereswasaround100nmto300nm.InFig.2B,itcouldbeseenclearlythattheBiOClwasdominatedwithsurfacesmoothplatesandthethicknessisabout50nm.InFig.2C,the7wt%PANI/BiOClwasmainlycomposedofmanyplateswithmanysmallparticlesdispersiononthesurfaceofplates.

Fig.3showstheFT-IRspectraofPANI,BiOCland7wt%PANI/BiOCl.Thestrongpeaksatlowfrequency（about500cm−1）wereattributedtotheBi-OvibrationofchemicalbondsinBiOCl[28].ThespectraofPANImainlyincludedthecharacteristicabsorptionbandsasfollowing:

1554cm−1（C＝Cstretchingmodeforthequinonoidunit）,1479cm−1（C＝Cstretchingmodeforbenzenoidunit）,1298cm−1and1242cm−1（C-Nstretchingmodeofbenzenoidunit）and1122cm−1（aplanebendingvibrationofC-H）[29].Forthespectrumof7wt%PANI/BiOCl,thecharacteristicpeaksofPANIat1554cm−1,1479cm−1,1298cm−1,1242cm−1and1122cm−1alsoappeare