First-principles study on the synergistic effects of codoped

First-principlesstudyonthesynergisticeffectsofcodopedanataseTiO2photocatalystscodopedwithN/VorC/Cr

XuWenhui(许文慧)1,MaXinguo(马新国)1; ,WuTong(吴桐)1,HeZhiqi(贺之琦)1,WangHuihu(王辉虎)2,andHuangChuyun(黄楚云)1;3;

1School2School

ofScience,HubeiUniversityofTechnology,Wuhan430068,China

ofMechanicalEngineering,HubeiUniversityofTechnology,Wuhan430068,China

3HubeiCollaborativeInnovationCenterforHigh-EfficientUtilizationofSolarEnergy,HubeiUniversityofTechnology,Wuhan430068,China

Abstract:Aneffectivecompensatedcodopingapproachisdescribedtomodifythephotoelectrochemicalprop-ertiesofanataseTiO2bydopingwithnonmetals(NorC)andtransitionmetals(VorCr)impurities.Here,com-pensatedcodopedTiO2systemsareconstructedwithdifferentdopantspeciesandsources,andthentheirdopantformationenergiesandelectronicstructuresareperformedtostudythestabilityandvisible-lightphotoactivitybyfirst-principlesplane-waveultrasoftpseudopotentialcalculations,respectively.Thecalculatedresultsdemonstratethatthecodopingwithtransitionmetalsfacilitatestheenhancementoftheconcentrationofp-typedopants(NandC)inahostlattice.Especially,compensatedcodopingnotonlyreducestheenergygap,toenhancetheopticalab-sorption,andeliminatethelocaltrapping,toimprovecarriermobilityandconversionefficiency,butitalsokeepstheoxidation-reductionpotentialoftheconductionbandedge.TheseresultsareconducivetotheunderstandingofthesynergisticmechanismofthephotocatalyticactivityofTiO2thatisenhancedbycodoping.Keywords:first-principles;photocatalysis;TiO2;codopingDOI:10.1088/1674-4926/35/10/102002PACC:6170;7155;7125

1.Introduction

AnataseTiO2hasattractedextensiveattentionasapromis-ingactivesemiconductorphotocatalystinthefieldsofphoto-catalysistechnology 1;2 ,dye-sensitizedsolarcells 3;4 andso

on,foritsexcellentphotoelectricandphotocatalyticproperties.However,itisnecessarytomodifythepropertiesofTiO2duetoitswidebandgap(3.23eV)andhighrecombinationrateofphotogeneratedelectron–holepairs.PreviousstudieshavemostlyfocusedontheionmonodopingofTiO2 5 8 ,whichusuallycannotsimultaneouslybroadentheabsorptionspectraofvisiblelightandincreasethephotoquantumyieldvalue.Recently,codopedTiO2withnonmetalsandtransitionmetalshasbecomearapidlygrowingfieldofinterestforexperimentalstudies.Theresultsindicatethatthecodopingwithnonmetalsandtransitionmetalscanimprovethephotocatalyticperfor-mancesofTiO2.Forexample,photocatalyticactivityhasbeenincreasedby10timesthroughtheincorporationofFeintononmetal-dopedTiO2thinfilms 9 .Moreover,byusingthesol-gelmethod,V/Si-dopedTiO2thinfilmshavebeenpreparedbythesol–gelmethod,showingthatthecodopedthinfilmshavehigherphotocatalyticperformancesthanmonodopedsys-tems 10 .So,itisaneffectivewaytomodulatesemiconduc-torphotoelectricresponsebynonmetalsandtransitionmetalscodoping.

Theexperimentalresultsindicatethatcodopinghasacer-taineffectontheabsorptionspectraandphotocatalyticactiv-ityofTiO2 9 12 .However,themechanismofdopingisstill

unclearbecausethedifferentpreparationprocessesandexper-imentalconditionshavecomplexinfluencesonthephotocat-alyticpropertiesofTiO2.Avarietyofnegativeexperimentfac-torscanberesolvedusingthefirst-principlesmethodtoana-lyzetheeffectofdopingontheelectronicstructuresandopti-calproperties 13;14 .Gaietal. 15 usedthecompensateddonor-acceptorcodopingmethodbasedonthefirst-principlescalcu-lationstoexplaintheeffectsofMo/http://doc.guandang.net-pensateddonor-acceptorcodopingmeansthattheelectronsonthedonorlevelscompensatethesameamountofholesontheacceptorlevels,sothatthesystemstillkeepsasemiconduc-torcharacter.Theconceptsofcompensateddonor–acceptorcodopinghavebeenestablishedasthepowerfulguidingprin-cipleinthefuturedesignofphotocatalystsandotherfunc-tionalmaterials.Veryrecently,V/N-codopedTiO2photocata-lystshavebeensynthesizedbyGuetal. 16 ,whodemonstratedtheenhancementofphotocatalyticactivityforthedegradationofmethyleneblueundervisible-lightirradiation( >440nm)comparedwiththoseofV-dopedTiO2andN-dopedTiO2.Fur-therstudyoftheelectronicstructureofN/V-dopedTiO2hasbeenimplemented,thestudyofthesynergisticeffectofV/N-codopedanataseTiO2photocatalystspointedoutthatthein-corporationofVintoN-dopedTiO2candecreasetheformationenergyofN-doping,andthusincreasetheN-dopingconcentra-tions,whichcouldimprovetheabsorptionintensityofanataseTiO2 17 .Thecodopedsystems,suchas(V,N),(Cr,N),and(Mn,N),havebeenproposed,whichhasdemonstratedthatthecodopedsystemshaveimpurityenergylevelswithasignificant

*ProjectsupportedbytheNationalNaturalScienceFoundationofChina(Nos.51102150,51202064),theNationalPost-DoctoralScienceFoundationofChina(No.201104085),andtheChutianScholarProgram(No.GCRC13014). Correspondingauthor.Email:maxg2013@http://doc.guandang.net,chuyunh@http://doc.guandang.netReceived27February2014,revisedmanuscriptreceived21April2014©2014ChineseInstituteofElectronics

bandwidth 18 .AlthoughV/N-codopedTiO2hasbeenrevealedasapromisingphotoactivematerialinchemicalreactions,theunderstandingofthephotoresponsemechanismsisratherlim-ited.Inthepresentwork,wehavecalculatedthedopantde-fectformationenergiesoftheV/N-andCr/C-codopedTiO2usingfirst-principles,withtheaimofdiscussingthestabilityofcodopingsystemsandtheeffectofcodopingontheimpurityconcentration.Furthermore,theelectronicandopticalproper-tiesofV/N-andCr/C-codopedTiO2hasbeeninvestigatedtocomparewiththoseofpureandmonodopedTiO2torevealhowtheseimpuritiesaffecttheenergybandstructuresofanataseTiO2.

2.Calculationmodelsandmethods

Allofthecalculationswereperformedwiththeplane-waveultrasoft(PWUS)pseudopotentialmethod 19 ,whichisbasedonthedensityfunctionaltheory(DFT),andthecodewasimplementedinCASTEP 20 .Theelectronicexchange-correlationenergywasdescribedbythegeneralgradientap-proximation(GGA)withPW91 21 becausethegeometrystructureparametersofTiO2calculatedbyPW91areclosertotheexperimentalvalue 22 thanthosecalculatedbyPBE 23 andRPBE 24 schemes 25 .Inaddition,theenergycutoffforaplanewavewassetas380.0eV.Todescribetheion-electroninteraction,theval …… 此处隐藏：25901字，全部文档内容请下载后查看。喜欢就下载吧 ……