Facet Effect of Single-Crystalline Ag3PO4 Sub-microcrystalso

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FacetEffectofSingle-CrystallineAg3PO4Sub-microcrystalsonPhotocatalyticProperties

YingpuBi,ShuxinOuyang,NaotoUmezawa,JunyuCao,andJinhuaYe*

InternationalCenterforMaterialsNanoarchitectonics(MANA)andPhotocatalyticMaterialsCenter,NationalInstituteforMaterialsScience(NIMS),1-2-1Sengen,Tsukuba,Ibaraki305-0047,Japan

SupportingInformationb

ABSTRACT:WerecentlyreportedthatAg3PO4exhibitsexcellentphotooxidativecapabilitiesforO2evolutionfromwaterandorganicdyedecompositionundervisible-lightirradiation.However,verylittleisknownabouttheshapeandfacete ectsofAg3PO4crystalsontheirphotocatalyticproperties.Hereinwehavedevelopedafacileandgeneralrouteforhigh-yieldfabricationofsingle-crystallineAg3PO4rhombicdodecahedronswithonly{110}facetsexposedandcubesboundedentirelyby{100}facets.Moreover,studiesoftheirphotocatalyticperformancehaveindicatedthatrhombicdodecahedronsexhibitmuchhigheractivitiesthancubesforthedegradationoforganiccontaminants,whichmaybeprimarilyascribedtothehighersurfaceenergyof{110}facets(1.31J/m2)thanof{100}facets(1.12J/m2).

hemorphologyandcrystal-facet-controlledfabricationofsemiconductormaterialshaverecentlyattractedconsider-ableattentionbecausetheirphotoelectricandphotocatalyticpropertiescanbefurtherenhancedoroptimizedbytailoringthesurfaceatomicstructures.1À4Forexample,Luandco-workersdemonstratedthatthe{001}facetsofanataseTiO2aremuchmorereactivethanthethermodynamicallystable{101}facetsfortheproductionofH2fromwatersplitting.5À7Moreover,itwasreportedthatBiVO4nanoplateswithexposed{100}facetsexhibitedenhancedphotocatalyticactivityforthedecompositionofrhodamineB.8Althoughthesehighlyreactivefacetsaremoreinterestingandimportantforimprovingphotocatalyticreactivity,theyusuallydiminishrapidlyduringthegrowthprocessbecauseoftheirhighsurfaceenergies.9Toaddressthisissue,organicpolymersorinorganicionshaveusuallybeenemployedforselectivecontrolofthegrowthratesofvariousplanes.10,11However,thepercentageofhighlyreactivefacetsinthe nalproductshasstillbeenrelativelylow.Ontheotherhand,cappingagentsadsorbedonthesurfacesofsemiconductorcrystalsmustberemovedbycomplextreatmentsbeforetheircatalyticapplica-tions,andthehighlyreactivefacetsmaylosemanyoftheiractivesitesasaresultofsurfacereconstruction.Thus,thefabricationofphotocatalystswithonlyhighlyreactivefacetsexposedandwithoutcappingagentsisstillagreatchallenge.

Morerecently,wereportedthenewuseofAg3PO4semicon-ductorinphotocatalyticapplications,12whereitexhibitsextre-melyhighphotooxidativecapabilitiesforO2evolutionfromwaterandorganicdyedecompositionundervisible-lightirradia-tion.Morespeci cally,thisnovelphotocatalystcanachievequantume cienciesofupto90%atwavelengthsgreaterthan

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420nm,whichissigni cantlyhigherthanpreviouslyreportedvalues.However,becausetheas-preparedAg3PO4samplespossessedirregularandpolyhedralcrystalstructures,theshapeandfacete ectsontheirphotocatalyticpropertieshaveremaineduncleartodate.Hereinwedemonstrateafacileandgeneralprocedureforfabricationofsingle-crystallineAg3PO4rhombicdodecahedronswithonly{110}facetsexposedandcubesboundedby{100}facetsintheabsenceofanycappingagent.Furthermore,studiesoftheirphotocatalyticperformancehaveclearlyrevealedthattherhombicdodecahedronsexhibitsuperiorphotocatalyticpropertiesincomparisonwithcubesforthedegradationoforganiccontaminants.TheoreticalcalculationssuggestthatAg3PO4{110}facetsexhibitahighersurfaceenergythan{100}planes,whichmaycontributesigni cantlytotheenhancedphotocatalyticactivity.

Figure1AandFigureS1intheSupportingInformationshowtypicalscanningelectronmicroscopy(SEM)imagesoftheAg3PO4productssynthesizedbysimplyreactingsilveracetatewithNa2HPO4inaqueoussolutionsatroomtemperature.Itcanbeclearlyseenthatallofthesesamplespossessperfectandregularrhombicdodecahedralmorphologywithanaveragediameterof600nm,andsomeofthemself-assembledintotwo-dimensionallyorderedarrays.TheenlargedSEMimage(Figure1Ainset)revealsthattheas-preparedAg3PO4sub-microcrystalswereenclosedby12well-de ned{110}planeswithcubiccrystalsymmetryandsingle-crystalstructure.13Inter-estingly,asshowninFigure1BandFigureS2,whensilveracetatewasreplacedbysilverÀamminecomplexinthissyntheticsystem,uniformAg3PO4sub-microcubeswithsmoothsurfacesandsharpcornersandedgeswerefabricatedinlargequantities.Further-more,itcanbeclearlyseen(Figure1Binset)thattheAg3PO4sub-microcubeswereboundedcompletelybysixsquare{100}facets.ThebasicstructuralunitsofboththeAg3PO4rhombicdodecahedronsandcubesareshowninFigureS3.Withexten-sionoftheirfacetsalongthree-dimensionalspace,thecorre-spondinglargeAg3PO4sub-microcrystalscanbeperfectlyconstructed.Moreover,theirenergy-dispersivespectroscopy(EDS)results(seeFigureS4)indicatethatexceptfortheelementsCuandZnfromthesupports,onlyAg,O,andPelementsweredetected.Furthermore,theX-raydi raction(XRD)patterns(Figure1C)clearlyshowthatallofthedi rac-tionpeaksoftherhombicdodecahedralandcubicsamplescouldbeindexedtothebody-centeredcubicstructureofAg3PO4(JCPDSno.06-0505).However,itisworthnotingthatobvious

Received:January9,2011Published:April12,2011

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Figure3.Relaxedgeometriesforthe(A){110}and(B){100}surfacesofAg3PO4basedona192-atomslabmodel.Thevacuumregionwassettothesame

thickness

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Ag3PO4.

Figure1.(A,B)SEMimagesofAg3PO4sub-microcrystalswithdi erentmorphologies:(A)rhombicdodecahedrons;(B)cubes.(C)XRDpatterns.(D)UVÀvisdi usivere ectancespectra.

Figure2.PhotocatalyticactivitiesofAg3PO4rhombicdodecahedrons,cubes,andspheresandN-dopedTiO2for(A)MOand(B)RhBdegradationundervisible-lightirradiation(λ>420nm).

changesintheintensityratiosforvariouspeakswereobserved,givingfurthersupporttotheaboveSEMobservations.Morespeci cally,inthecaseofrhombicdodecahedrons,theintensityratioof2.7forthe(110)and(200)di ractionswasremarkablyhigherthanthepowderintensityratio(0.78),con rmingthatth …… 此处隐藏：11781字，全部文档内容请下载后查看。喜欢就下载吧 ……