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BiVO4–Ru SrTiO3 Rh composite Z-scheme photocatalyst for solar

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BiVO4–Ru SrTiO3 Rh composite Z-scheme photocatalyst for solar3rbwoaongeoiciVtynenergyisconvertedtochemicalenergyaccompaniedwithalargepositivechangeintheGibbsplitting.Therefore,photocatalytarticialphotosynthesis.SpecicsystemwillbeadvantageousforlwatersplittingbecauseofitssimAtthepresentstage,alotofactivityforwatersplit...

BiVO4–Ru SrTiO3 Rh composite Z-scheme photocatalyst for solar
3rbwoaongeoiciVtynenergyisconvertedtochemicalenergyaccompaniedwithalargepositivechangeintheGibbsplitting.Therefore,photocatalytarticialphotosynthesis.SpecicsystemwillbeadvantageousforlwatersplittingbecauseofitssimAtthepresentstage,alotofactivityforwatersplittinghavemostofthephotocatalystsonlyrimportanttodevelopvisible-lighordertoharvestsunlightefficienAlthoughvisible-light-driventingsuchasRhxCryO/(GaN)x(ZnOnumberofphotocatalystsisvevisible-light-drivenphotocatalysevolutionreactions,thehalfreabeendeveloped.ForexampleAgNbO3,10SrTiO3:Cr,Ta,11TiO2:systemsemployionicelectronmediatorssuchasIO3�/I�,Fe3+/ChemicalScienceEDGEARTICLEPublishedon09December2013.Downloadedon8/4/20198:58:20AM.aDepartmentofAppliedChemistry,FacultyoKagurazaka,Shinjuku-ku,Tokyo162-8601,bPhotocatalysisInternationalResearchCenTechnology,TokyoUniversityofScience,268510,Japan†Electronicsupplementaryinforma10.1039/c3sc52810cThisjournalis©TheRoyalSocietyofCsfreeenergythroughthewatericwatersplittingisregardedasally,apowderedphotocatalystarge-scaleapplicationsofsolarplicityoffabrication.2,3photocatalyststhatshowhighbeendeveloped.4,5However,espondtoultravioletlight.Itist-responsivephotocatalystsintly.photocatalystsforwatersplit-)1�x6havebeenreported,therylimited.Incontrast,manytsforsacricialH2andO2ctionsofwatersplitting,have,WO3,7BiVO4,8TiO2:Cr,Sb,9Rh,Sb,12SrTiO3:Rh,13TaON,14Fe2+,[Co(bpy)3]3+/2+and[Co(phen)3]3+/2+redoxcouples.17–33TheelectronmediatorplaysanimportantroleinelectrontransferfromanO2-evolvingphotocatalysttoaH2-evolvingphotocatalyst.However,theelectronmediatoralsogivesnegativeeffects,suchasbackward-reactionsofwatersplittingandtheshieldingofincidentlight.Inmostcases,moreover,electronmediatorsworkatonlyalimitedpHrange.AuniqueZ-schemephotocatalystsystemforwatersplittinghasalsobeendevelopedbyemployingelectroconductivephotoreduced-grapheneoxide(PRGO)asasolidelectronmediatorforshuttlingelectrons,aH2-evolvingphotocatalyst(Ru/SrTiO3:Rh)andanO2-evolvingphotocatalyst(BiVO4).34WehavealsoreportedanewtypeofZ-schemephoto-catalystsystemdrivenbyinterparticleelectrontransfer(IPET)betweenaH2-evolvingphotocatalyst(Ru/SrTiO3:Rh)andanO2-evolvingphotocatalyst(BiVO4)withoutanelectronmediator.35Inthissystem,onlySrTiO3:Rhwithp-typecharacter40functionsasaH2-evolvingphotocatalystatpresent.Z-schemephotocatalystsystemsconsistingofSrTiO3:RhandvariousO2-evolvingphoto-BiVO4–Ru/SrTiOphotocatalystfoQingxinJia,aAkihideIwaseaBiVO4–SrTiO3:RhcompositesinattachedontheBiVO4particlesmethodandaliquid–solidstaterewatersplittingundervisiblelightoptimumpHforthewatersplittiinterparticleelectrontransferfrombythosepreparationmethods.Ththecrystallinityandmorphologyshowedthehighestphotocatalytsingle-crystal-likeparticles.TheB1.6%at420nmandastableactiviexceptforphotocatalystpowderaIntroductionPhotocatalyticwatersplittingusingpowderedphotocatalystsandsemiconductorphotoelectrodeshasattractedattentionasacleanmethodofhydrogenproductionfromwater.1,2LightCitethis:Chem.Sci.,2014,5,1513Received9thOctober2013Accepted6thDecember2013DOI:10.1039/c3sc52810cwww.rsc.org/chemicalsciencefScience,TokyoUniversityofScience,1-3Japan.E-mail:a-kudo@rs.kagu.tus.ac.jpter,ResearchInstituteforScienceand41Noda-shi,Yamazaki,Chiba-ken278-tion(ESI)available.SeeDOI:hemistry2014:RhcompositeZ-schemesolarwatersplitting†andAkihikoKudo*abhichtheRh-dopedSrTiO3particlesofaH2-evolvingphotocatalystfanO2-evolvingphotocatalystwerepreparedbyanimpregnationction.ThecompositesshowedphotocatalyticactivityforZ-schematicrsimulatedsunlightirradiationwithoutanelectronmediator.Thewasneutral.WatersplittingoverthecompositeproceededviaanBiVO4toRu/SrTiO3:RhparticlesatthelargeinterfacialareaobtainedphotocatalyticwatersplittingactivityofthecompositedependedonfBiVO4.Thecompositepreparedbytheliquid–solidstatereactionactivity.Thiswasduetotheformationofwell-crystallizedBiVO4O4–Ru/SrTiO3:Rhcompositephotocatalystgaveaquantumyieldof.Thus,wehavedevelopedthesimplestsystemrequiringnoadditives,dwater,forphotocatalyticsolarwatersplitting.ATaO2N(A¼Ca,Sr,andBa)14andTa3N5.15,16WatersplittingundervisiblelightirradiationwithoutanysacricialreagentshasbeenachievedbyconstructionofaZ-schemephotocatalystsystem(two-stepphotoexcitation)composedofH2-andO2-evolvingphotocatalysts.17–39MostoftheZ-schemephotocatalystViewArticleOnlineViewJournal|ViewIssuecatalystssuchasTiO2,35TiO2:Cr,Sb,35TiO2:Rh,Sb,35WO3,35andIr/CoOx/Ta3N5(ref.36)alsoshowactivityforwatersplitting.TheactivityofthisZ-schemesystemstronglydependsonthedispersedstateofH2-andO2-evolvingphotocatalystsinthereactantsolution.ThehighestphotocatalyticactivityisobtainedwhentwotypesofphotocatalystparticlesareaggregatedwithChem.Sci.,2014,5,1513–1519|1513suitablecontactunderacidicpHconditions.Incontrast,thisZ-schemephotocatalystsystemshowspooractivityunderneutralpHconditionsinpurewater,becausethephotocatalystparticlesareindependentlysuspended.Therefore,weareinterestedinconstructinganewandsimplecompositeZ-schemephoto-catalystsysteminwhichtheH2-evolvingphotocatalyst(Ru/SrTiO3:Rh)andO2-evolvingphotocatalyst(BiVO4)particlesstronglyattachtoeachothertosolvetheproblemofthepoorcontactbetweentwotypesofphotocatalystparticles.driedpowderwascalcinedat673Kfor2hinair,resultinginthe(Wakopurechemical;99.0%)powderwasaddedto0.5molL�1ofanaqueousnitricacidsolutionofBi(NO3)3(Kantochemical;99.9%).Thesuspensionwasstirredatroomtemperaturefor5days.Then,aBiVO4–Ru(0.7wt%)/SrTiO3:Rh(1%)compositephotocatalyst(Composite-LSR)wasobtained.TheowchartofthecompositepreparationandtheirabbreviatednamesareshowninFig.S1.†TheobtainedcompositepowderwasconrmedbyX-raydiffractionusingCuKaradiation(XRD;Rigaku;MiniFlex).PhotocatalyticwatersplittingwasalsocarriedoutusinganaatWv�ChemicalScienceEdgeArticlePublishedon09December2013.Downloadedon8/4/20198:58:20AM.ViewArticleOnlineformationoftheBiVO4–Ru(0.7wt%)/SrTiO3:Rh(1%)composite(Composite-Imp).Theobtainedcompositephotocatalystwasacid-treatedin0.5molL�1ofanaqueousnitricacidsolutionfor5days(Composite-Imp-AT),ifnecessary.Inthecaseofaliquid–solidstatereaction,8BiVO4waspreparedinthepresenceofRu-loadedSrTiO3:Rhpowder.Ru(0.7wt%)/SrTiO3:Rh(1%)andV2O5Solarenergyconversionefficiency%¼½Output½Energydensityofincidentsol¼½DG0ðH2OÞ=Jmol�1��½R3600�½SolarenergyðAM1:5Þ=¼½237kJmol�1��½RateofH2e3600�½100mWcm�2Inthepresentstudy,aBiVO4–Ru/SrTiO3:Rhcompositewaspreparedbyanimpregnationmethodandaliquid–solidstatereactioninordertoconstructasimplephotocatalystsystemforwatersplittingundervisiblelightirradiation.Solarwatersplittingwasalsodemonstratedusingthepresentcompositephotocatalyst.ExperimentalPreparationandcharacterizationofphotocatalystsSrTiO3:Rh(1%)asaH2-evolvingphotocatalystwaspreparedbyasolid–statereactionaspreviouslyreported.13ThestartingmaterialsofSrCO3(Kantochemical;99.9%),TiO2(Soekawachemical;99.9%)andRh2O3(Wakopurechemical)weremixedinamortarattheratioofSr–Ti–Rh¼1.03:0.99:0.01.Themixturewascalcinedat1273Kfor10hinairusinganaluminacrucible.ARu(0.7wt%)cocatalystworkingasanactivesiteforH2evolutionwasloadedonSrTiO3:Rh(1%)byphotodepositionfromanaqueousmethanolsolution(10vol%)containingRuCl3$nH2O(TanakaKikinzoku).31,35TheRucocatalyst-loadedphotocatalystwascollectedbyltrationandwashedwithwater.BiVO4ofanO2-evolvingphotocatalystwascombinedwithRu(0.7wt%)/SrTiO3:Rh(1%)byanimpregnationmethodandaliquid–solidstatereaction.Inthecaseoftheimpregnationmethod,Bi(NO3)3(Kantochemical;99.9%)andNH4VO3(Kantochemical;99.0%)atanequalmolarratioweredissolvedin4molL�1ofanaqueousnitricacidsolution(Kantochemical)asaprecursorsolution.TheconcentrationsofBi3+andV5+ionswere0.4mmolL�1.TheRu(0.7wt%)/SrTiO3:Rh(1%)powderandadesiredamountoftheprecursorsolutionwereputintoaporcelaincrucible.Waterwasevaporatedinawaterbath.The1514|Chem.Sci.,2014,5,1513–1519Arowsystemandasolarsimulatorwithanair-mass1.5lter(PeccellTechnologies;PEC-L11,100mWcm�2).ThesolarwatersplittingwasconductedusingatopirradiationcellwithaPyrexwindowwithanirradiationareaof33cm2.TheamountofevolvedH2andO2weredeterminedwithgaschromatography(Incon;3000MicroGC,MS-5Acolumn,Arcarrier,TCD).Thesolarenergyconversionefficiency(STH)wasdenedbyeqn(2).energyasH2=J�rlight=Jcm-2��½Irradiatedarea=cm2��100eofH2evolution=molh�1�cm�2��½Irradiatedarea=cm2��100olution=mmolh�1��½33cm2��100(2)SurfaceareasweredeterminedbyBETmeasurements(Coulter;SA3100).Photocatalystparticlesxedwithcarbonpasteonasampleholderwereobservedbyscanningelectronmicroscopy(SEM;Jeol;JSM-6700F).Diffusereectancespectra(DRS)wereobtainedusingaUV-Vis-NIRspectrometer(JASCO;Ubest-570)andwereconvertedfromreectiontoabsorbancebytheKubelka–Munkmethod.PhotocatalyticreactionsPhotocatalyticreactionsweremainlyconductedinagas-closed-circulationsystemandatopirradiationcellwithaPyrexwindow.Photocatalystpowders(0.2–0.4g)weresuspendedinwater(150mL).Ifnecessary,thepHofthereactantsolutionwasadjustedwithH2SO4(Kantochemical)andNaOH(Kantochemical).Thelightsourcewasa300WXe-lamp(ILCtech-nology;CERMAXLX-300).Theirradiationwavelengthwascontrolledbyacombinationofacoldmirrorandacut-offlter(420nm#l#800nm).TheamountsofevolvedH2andO2weredeterminedwithgaschromatography(Shimadzu;GC8A;MS-5Acolumn,Arcarrier,TCD).A300WXe-lamp(AshahiSpectra;MAX-301)withband-passlterswasemployedformeasure-mentofanapparentquantumyield(AQY).Thenumberofincidentphotonswasmeasuredusingaphoto-diodehead(OPHIRA;PD300-UV)andapowermonitor(NOVA).AQYwascalculatedaccordingtoeqn(1).Apparentquantumyield%¼½Thenumberofreactedelectronsorholes�½Thenumberofincidentphotons��100(1)Thisjournalis©TheRoyalSocietyofChemistry2014ResultsanddiscussionPreparationandcharacterizationofthecompositeFig.1showstheXRDpatternsofBiVO4–Ru/SrTiO3:Rhcompos-itespreparedbyanimpregnationmethodandaliquid–solidstatereaction.ThecombinedamountofBiVO4was250wt%toRu(0.7wt%)/SrTiO3:Rh(1%).Theratioinweightwas2.5:1.Inthiscase,themolarratioofBiVO4toSrTiO3:Rhwasabout1.4:1.AllsamplesgavethediffractionpatternofBiVO4withascheelitestructureandamonoclinicphase(s–m)whichshowedahighphotocatalyticactivity,8,41inadditiontothepatternofSrTiO3:Rhwithaperovskitestructure.Thefullwidthsathalfmaximaofthe(110),(011),(002)and(200)peaksfortheComposite-Imp-AT(Fig.S2(B)†)andtheComposite-LSR(Fig.S2(C)†)werenarrowerthanthosefortheComposite-Imp(Fig.S2(A)†),indicatingthehighercrystallinityofBiVO4inComposite-Imp-ATandComposite-LSRcomparedtoComposite-Imp.Fig.2showsSEMimagesofBiVO4–Ru/SrTiO3:Rhcompositespreparedbyanimpregnationmethodandaliquid–solidstatereaction.Ru(0.7wt%)/SrTiO3:Rh(1%)withoutBiVO4(Fig.2(A))andaphysicalmixtureofBiVO4withRu(0.7wt%)/SrTiO3:thetwotypesofparticlewereseparatedfromeachother(Fig.2(G)).ThemorphologyoftheobtainedBiVO4dependedonthepreparationmethodofthecomposite.BiVO4oftheComposite-Impwasanaggregateofsmallparticleswitharoundshapeandhadmanygrainboundaries(Fig.2(B)).Theaggre-gatedBiVO4particlesoftheComposite-Impbecamecrystallineplateparticleswithamicrometersizeaerstirringinanaqueousnitricacidsolutionfor5daystogivetheComposite-Imp-AT(Fig.2(C)).Itwasduetothedissolution–reprecipitationprocessoftheBiVO4particles.BiVO4oftheComposite-LSRwasasingle-crystal-likepolyhedralparticlereectingthecrystalstructureofthes-mphase(Fig.2(D)).Importantly,Ru/SrTiO3:Rhparticleswerepartlywrappedwiththesingle-crystal-likeBiVO4particles(Fig.2(E)),givingalargeinterfacialareaandgoodcontactbetweentheRu/SrTiO3:RhandBiVO4particles.Fig.2Scanningelectronmicroscopeimagesof(A)Ru(0.7wt%)/SrTiO3:Rh,(B)–(F)BiVO4(250wt%)-Ru(0.7wt%)/SrTiO3:Rh(1%)composites,and(G)aphysicalmixtureofBiVO4+Ru(0.7wt%)/SrTiO3:Rh(1%).Preparationmethods:(B)impregnation(Composite-Imp),(C)nitricacidtreatmentatroomtemperaturefor5daysafterimpregnation(Composite-Imp-AT),and(D,EandF)aliquid–solidstatereaction(Composite-LSR).(F)Afterphotocatalyticreaction.SrTiO3:Rhwaspreparedbysolidstatereactionat1273Kfor10h.TheRucocatalystwasloadedbyphotodeposition.EdgeArticleChemicalSciencePublishedon09December2013.Downloadedon8/4/20198:58:20AM.ViewArticleOnline3preparedbyasolidstatereactionat1273Kfor10h.Rucocatalystwasloadedbyphotodeposition.Rh(1%)powder(Fig.2(G))werealsoobservedasreferencesamples.TheSrTiO3:Rh(1%)particlewithoutBiVO4preparedbyasolid–statereactionwasanaggregateofprimaryparticleswithabout100nmoftheparticlesize(Fig.2(A)).Twokindsofparticleswithdifferentshapesandparticlesizeswereobservedforthecomposites(Fig.2(B–F)).SEM-EDSmappingswerecarriedoutforthesamplesofFig.2(B)and(D)toexaminetheseparticles(Fig.S3†).TheparticleswereidentiedasBiVO4andSrTiO3:Rh.ItwasconrmedthatBiVO4particlesofabout100nanometersfortheComposite-Imp(Fig.2(B))and1–2micrometersfortheComposite-LSR(Fig.2(DandE))werecombinedwiththeRu/SrTiO3:Rhparticles.Thus,SrTiO3:Rh(1%)wassuccessfullycombinedwithBiVO4bytheimpregnationmethodandtheliquid–solidstatereaction(Fig.2(B–F)),whichdifferedfromthephysicalmixtureinwhichFig.1X-raydiffractionpatternsoftheBiVO4(250wt%)-Ru(0.7wt%)/SrTiO3:Rh(1%)compositeZ-schemephotocatalyst.Preparationmethods:(A)impregnation(Composite-Imp),(B)nitricacidtreatmentatroomtemperaturefor5daysafterimpregnation(Composite-Imp-AT),and(C)aliquid–solidstatereaction(Composite-LSR).SrTiO:RhwasThisjournalis©TheRoyalSocietyofChemistry2014Chem.Sci.,2014,5,1513–1519|1515Thus,thecompositeofRu/SrTiO3:RhandBiVO4withsuitableChemicalScienceEdgeArticlePublishedon09December2013.Downloadedon8/4/20198:58:20AM.ViewArticleOnlinecontactwassuccessfullyobtainedbyfacilemethods.Table1WatersplittingusingtheBiVO4–Ru/SrTiO3:Rh(1%)compositeZ-schemephotocatalystundervisiblelightirradiationaEntryPhotocatalystRatioofBiVO4toRu/SrTiO3:RhinweightActivity/mmolh�1H2O21Composite-Imp1.05.02.22Composite-Imp1.510.04.33Composite-Imp2.015.87.54Composite-Imp2.523.811.75Composite-Imp3.011.45.46Composite-Imp-AT2.533.215.37Composite-LSR2.045.821.28Composite-LSR2.547.222.49HeatedComposite-LSR2.519.29.110Composite-LSR3.040.818.511Composite-LSR3.539.017.212Ru/SrTiO3:Rhonly—0.10.013Physicalmixture1.03.01.114Physicalmixture2.54.52.115Heatedphysicalmixtureb2.51.00.416Heatedphysicalmixturec2.50.90.4aCatalytst:0.2–0.4g;water:150mL(pHwasnotadjusted);lightsource:300WXe-arclampwithacoldmirrorandacut-offlter(420nm#l#800nm);reactor:topirradiationcellwithaPyrexwindow.bHeat-treatedphysicalmixtureofBiVO4andRu/SrTiO3:Rh.cPhysicalmixtureofnon-heat-treatedBiVO4andheat-treatedRu/SrTiO3:Rh.Conditionsofheating,573Kfor1hinair.PhotocatalyticwatersplittingTable1showswatersplittingundervisiblelightirradiationusingtheBiVO4–Ru/SrTiO3:Rh(1%)compositeZ-schemepho-tocatalystspreparedbyseveralmethods.Allcompositesshowedphotocatalyticactivities(entries1–11).Theactivitystronglydependedonthepreparationmethod(entries4,6and8)andtheratioofBiVO4toRu/SrTiO3:Rh(entries1–5,7,8,10and11).TheComposite-Imp-AT(entry6)showedahigheractivitythantheComposite-Imp(entry4).Theacid-treatmentofstirringintheaqueousnitricacidsolutionimprovedthecrystallinityofBiVO4.Therefore,therecombinationprobabilityofphoto-generatedelectronsandholeswassuppressed,resultinginanincreaseintheactivityofBiVO4.Suchimprovementofphoto-catalyticactivityviaacid-treatmenthasbeenseeninthecaseofame-madeBiVO4.42Thecompositephotocatalystpreparedbyaliquid–solidstatereaction(Composite-LSR)showedthehighestphotocatalyticactivity(entry8)amongthecomposites.ThiswasduetofurtherimprovementofthecrystallinityofBiVO4andbettercontactasobservedinFig.2(D)and(E).WealsocheckedtheComposite-LSRaerphotocatalyticwatersplittingbySEM(Fig.2(F)).BiVO4andRu/SrTiO3:Rhremainedasastablecomposite.TheseresultsindicatethattheBiVO4andRu/SrTiO3:RhparticlesinthecompositestayedtogetherevenunderneutralpHconditions,resultinginanefficientelectrontransferbetweentheRu/SrTiO3:RhandBiVO4particles.Entries1–5,7,8,10and11inTable1showthedependenceofphotocatalytic1516|Chem.Sci.,2014,5,1513–1519activityontheratioofBiVO4toRu/SrTiO3:Rh.Thehighestactivitywasobtainedwhentheratiowas2.5inweight(themolarratioofBiVO4toSrTiO3:Rhwasabout1.4:1)forbothpreparationmethods.Thisdependenceontheratiowasprob-ablyduetothebalanceoftheamountofcontactareabetweentheRu/SrTiO3:RhandtheBiVO4particlesandthenumberofphotonsabsorbedbyeachphotocatalyst.Forcomparison,thephotocatalyticactivityoftheRu(0.7wt%)/SrTiO3:Rh(1%)powderandRu(0.7wt%)/SrTiO3:Rh(1%)physicallymixedwithBiVO4powder(physicalmixture)wasalsoexamined.Photo-catalyticwatersplittingdidnotproceedusingRu/SrTiO3:RhwithoutBiVO4(entry12).13InthepresenceofBiVO4,H2andO2evolvedfromwater(entries13and14).ItisreportedthattheactivityunderneutralpHconditionsislowerthanthatunderacidicconditionsbecauseofpoorcontactbetweentheSrTiO3:RhandBiVO4particlesforthesampleofthephysicalmixture.35Therefore,weexaminedtheeffectofheat-treatmentinairforthesampleofthephysicalmixture,becausetheheat-treatmentwouldhavegivenagoodcontactbetweentheBiVO4Fig.3DependenceofthephotocatalyticactivityoftheBiVO4(250wt%)-Ru(0.7wt%)/SrTiO3:Rh(1%)composite(Composite-LSR)Z-schemephotocatalystonpHadjustedwithH2SO4andKOH.Catalyst:0.3g;lightsource:300WXe-arclampwithacoldmirrorandacut-offfilter(420nm#l#800nm).andRu/SrTiO3:Rhinthephysicalmixture(entries15and16).However,theactivitywasdecreasedbytheheat-treatment.Thisresultismainlyduetothedegradationofcocatalysts,becausetheactivityofthephysicalmixtureofnon-heat-treatedBiVO4andheat-treatedRu/SrTiO3:Rh(entry16)wasquitelow.Wehavealsoexaminedtheeffectofheat-treatmentinairforthesampleofComposite-LSRshowingthehighestactivity(entry9).Theactivitywasalsodecreasedbytheheat-treatment.Thisresultisthesameasthatoftheheat-treatedphysicalmixture.Thephotocatalyticactivityforwatersplittingusingthepresentcomposite(Composite-LSR)undervisiblelightirradia-tiondependedonthepHoftheaqueoussolutionasshowninFig.3.ThehighestandmoststableactivitywasobtainedunderneutralpHconditions(Fig.S4†).ThispHdependencewasdifferentfromthatofamixtureofRu/SrTiO3:RhandBiVO4powder(physicalmixture),35showingitshighestactivityatpH3.5.Asmentionedabove,acidicpHconditionswererequiredforthephysicalmixturetogainfavorablecontactbyaggregation.Incontrast,sincethecompositesoriginallypossessedsuitableThisjournalis©TheRoyalSocietyofChemistry2014solution(TableS1†).AsthepHincreased,theactivitiesofRu/SrTiO3:RhandBiVO4increasedanddecreased,respectively.Moreover,BiVO4dissolvedinbasicconditionsabovepH10.AsthebalancebetweenthepositiveandnegativeeffectsofpH,theoptimumpH7wasobtained.WealsoexaminedtheeffectsoftheadditionofanelectrolytesuchasK2SO4.TheactivityinanaqueousK2SO4solutionatpH7wascomparablewiththatinpurewater.Thisresultindicatesthenegligibleeffectofanelectrolyteontheactivityinthepresentphotocatalystsystem.Therefore,itisconcludedthatthedecreaseintheactivityunderacidicandbasicconditionswasnotduetothepresenceoftheelectrolytebutduetopH.Fig.4showsanactionspectrumforwatersplittingusingthecompositephotocatalyst.ThediffusereectionspectrumofthecompositephotocatalystagreedwiththesumofthediffusereectionspectraofBiVO4(Fig.S5(B)†)andSrTiO3:Rh(1%)Fig.4Photoresponseofthecomposite(Composite-LSR)Z-schemephotocatalysissystem.(A)Actionspectrumofwatersplitting;(B)thediffusereflectionspectrumoftheBiVO4(250wt%)-Ru(0.7wt%)/SrTiO3:Rh(1%)compositeZ-schemephotocatalystsystem.EdgeArticleChemicalSciencePublishedon09December2013.Downloadedon8/4/20198:58:20AM.ViewArticleOnlinecontactbetweenBiVO4andRu/SrTiO3:Rhparticlesforelectrontransfer,theyshowedwatersplittingactivityunderawiderangeofpHconditions.WemeasuredtheeffectsofpHonsacricialH2andO2evolutionoverRu/SrTiO3:RhandBiVO4,toseewhetherthechangeinphotocatalyticactivityshowninFig.3wasduetothepHortheionicconcentrationintheaqueousFig.5SolarwatersplittingoverBiVO4(250wt%)-Ru(0.7wt%)/SrTiO3:Rh(1%)composite(Composite-LSR)Z-schemephotocatalyst.Catalyst:0.3g;lightsource:asolarsimulatorwithanAM1.5filter(100mWcm�2);reactor:topirradiationcellwithPyrexwindow;irradiationarea:33cm2;rateofArflow:30mLmin�1.Table2WatersplittingusingZ-schemephotocatalysissystemscompomediatorsundervisiblelightirradiationaEntryMediatorpHS
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