©Copyright1999bytheAmericanChemicalSocietyVOLUME103,NUMBER29,JULY22,1999

LETTERS

SilverBromideasaPhotocatalystforHydrogenGenerationfromCH3OH/H2OSolution

NoriyoshiKakuta,*NaokoGoto,HironobuOhkita,andTakanoriMizushima

DepartmentofMaterialsScience,ToyohashiUniVersityofTechnology,Tempaku,Toyohashi441-8580,JapanReceiVed:January25,1999;InFinalForm:April28,1999

AAgBr/SiO2catalystpreparedfromSchumannemulsionhasbeenusedforphotolysisofCH3OH/H2Osolution.UnderUVillumination,H2generationwasobservedandhydrogenwascontinuouslyevolvedfor200hwithoutdestructionofAgBralthoughAg0wasdetectedbyX-raydiffractionanalysisafterthereaction.ItispresumedthatthehydrogenproductionfrommethanolindistilledwateroccursontheAg0andthesupportplaysimportantrolesforthephotocatalysisaswellasTiO2/SiO2(J.Phys.Chem.B1997,101,2611).

Introduction

Silverhalidesarewell-knownasphotosensitivematerialsandwidelyemployedassourcematerialsinphotographicfilms.Thephotographicprocessinsilverhalidescomprisesbasicallythefollowing:Absorptionofaphotonliberatesanelectronandapositivehole.Theelectronwillcombinewithamobileinterstitialsilverion,leadingtoseparationofasilveratom.Uponrepeatedabsorptionofphotons,ultimatelyaclusterofsilveratomscanbeformed.Thisistheso-calledlatent-imagespeck.Thecriticalsize,whichwasinvestigatedbyFayetetal.,1isfoursilveratomsforthedevelopment.Thismeansthatsilverhalidesareunstableunderirradiationoflight,leadingtothecolorchangeofsilverhalideaftertheexposuretosunlight.Fromthoseproperties,silverhalideshavenotbeensomuchsubjectedtostudiesonthephotolysisofwatersuchasTiO22andCdS.3

Recently,Calzaferrietal.4reportedthatthinsilverchloridelayersonSnO2-coatedglassplatesevolvedO2inthepresenceofsmallexcessAg+ionsinaqueoussolutionundernear-UVillumination.TheroleofAg+ionswastosupplyAgClspeciestoperformcontinuousphotooxidationofwater.Thisindicatesthatsilverhalideshaveapotentialforwatersplittingunderirradiationifwecandiscoverasuitableconditiontoavoidthephotodecompositionofsilverhalides.Wehavethusemployed

*Authortowhomcorrespondenceshouldbe

addressed.

supported-silverhalidecatalyststoinvestigatewhetherornotthephotosensitivitycanbeavailableforwaterdecomposition.Inthisstudy,AgBr,whichwaspreparedusingaSchumannemulsion5describedinthefilmtechnology,wasdispersedonsilicasupportandCH3OH/H2Osolutionwasemployedtoexaminethephotocatalyticactivity.TheformationofH2wasobserved,andH2wascontinuouslyevolvedevenafterUVilluminationfor200h.ExperimentalSection

AgBremulsionwaspreparedaccordingtothepreparationmethodforaSchumanndryplate,5whichiswidelyusedforanUV-sensitivephotograph,becauseUVlightwasemployedinallexperiments.Inbrief,twosolutionswereprepared:Adequateamountsofpotassiumbromideandgelatinweredissolvedindistilledwaterat373K(solutionA)andanadequateamountofAgNO3wasalsodissolvedindistilledwaterat373K(solutionB).SolutionBwasslowlypouredintosolutionAundervigorousstirring,andthemixedsolutionwaskeptat373Kfor30minundermildstirring.Next,themixedsolutionwascooledwithicefor2htoformgel,andthenthegelpieceswerewrappedwithaclothtowashwithflowingwaterfor2h.Afterwashing,thesolidpieceswerecompletelydissolvedindistilledwaterat368K.Finally,AgBremulsionwaspreparedbyfiltrationusingafunnelpackedwithglasswool.

10.1021/jp990287qCCC:$18.00©1999AmericanChemicalSociety

PublishedonWeb07/07/1999