Facile synthesis of Ag2O-TiO2/sepiolite composites with enhanced visible-light photocatalytic properties

Article abstract of DOI:10.1016/S1872-2067(15)61015-4

Ag₂O-TiO₂/sepiolite heterostructure composites were synthesized by a simple two-step method at low temperatures (100-450 °C). Acid red G aqueous solution and gaseous formaldehyde were chosen as model organic pollutants to evaluate the photocatalytic performance of the as-prepared composites. The results showed that the Ag₂O-TiO₂/sepiolite exhibited enhanced photocatalytic activity over pure Ag₂O-TiO₂, TiO₂/sepiolite, and Ag₂O/sepiolite under visible-light irradiation (λ > 420 nm). The excellent photocatalytic efficiency of these composites can be ascribed to the synergistic effect between the heterojunction and the porous structure of the clay layers, which induced high adsorption and efficient charge separation. In addition, the active species involved in the degradation reaction have been investigated by photoluminescence spectroscopy and quenching experiments. A possible photocatalytic degradation mechanism of acid red G dye by the Ag₂O-TiO₂/sepiolite composite is also discussed.

Full text of DOI:10.1016/S1872-2067(15)61015-4

ChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228
ꢀ
ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
ꢀ
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
ꢀ
ꢀ
Article (Special Issue on Photocatalysis)
FacileꢀsynthesisꢀofꢀAg
2
O‐TiO /sepioliteꢀcompositesꢀwithꢀenhancedꢀ
2
visible‐lightꢀphotocatalyticꢀpropertiesꢀ
ꢀa
ꢀa
ꢀa,b,
ꢀa
YuꢀDu ,ꢀDandanꢀTang ,ꢀGaokeꢀZhang *,ꢀXiaoyongꢀWu
ꢀ
aꢀSchoolꢀofꢀResourcesꢀandꢀEnvironmentalꢀEngineering,ꢀWuhanꢀUniversityꢀofꢀTechnology,ꢀ122ꢀLuoshiꢀRoad,ꢀWuhanꢀ430070,ꢀHubei,ꢀChinaꢀ
bꢀStateꢀKeyꢀLaboratoryꢀofꢀSilicateꢀMaterialsꢀforꢀArchitectures,ꢀWuhanꢀUniversityꢀofꢀTechnology,ꢀ122ꢀLuoshiꢀRoad,ꢀWuhanꢀ430070,ꢀHubei,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Ag O‐TiO /sepioliteꢀheterostructureꢀcompositesꢀwereꢀsynthesizedꢀbyꢀaꢀsimpleꢀtwo‐stepꢀmethodꢀatꢀ
Articleꢀhistory:ꢀ
2
2
Receivedꢀ17ꢀAugustꢀ2015ꢀ
Acceptedꢀ11ꢀNovemberꢀ2015ꢀ
Publishedꢀ20ꢀDecemberꢀ2015ꢀ
lowꢀtemperaturesꢀ(100–450ꢀ°C).ꢀAcidꢀredꢀGꢀaqueousꢀsolutionꢀandꢀgaseousꢀformaldehydeꢀwereꢀcho‐
senꢀ asꢀ modelꢀ organicꢀ pollutantsꢀ toꢀ evaluateꢀ theꢀ photocatalyticꢀ performanceꢀ ofꢀ theꢀ as‐preparedꢀ
composites.ꢀ Theꢀ resultsꢀ showedꢀ thatꢀ theꢀ Ag
activityꢀoverꢀpureꢀAg O‐TiO ,ꢀTiO /sepiolite,ꢀandꢀAg
20ꢀnm).ꢀTheꢀexcellentꢀphotocatalyticꢀefficiencyꢀofꢀtheseꢀcompositesꢀcanꢀbeꢀascribedꢀtoꢀtheꢀsyner‐
2 2
O‐TiO /sepioliteꢀ exhibitedꢀ enhancedꢀ photocatalyticꢀ
2
2
2
2
O/sepioliteꢀunderꢀvisible‐lightꢀirradiationꢀ(λꢀ>ꢀ
4
Keywords:ꢀ
gisticꢀeffectꢀbetweenꢀtheꢀheterojunctionꢀandꢀtheꢀporousꢀstructureꢀofꢀtheꢀclayꢀlayers,ꢀwhichꢀinducedꢀ
highꢀadsorptionꢀandꢀefficientꢀchargeꢀseparation.ꢀInꢀaddition,ꢀtheꢀactiveꢀspeciesꢀinvolvedꢀinꢀtheꢀdeg‐
radationꢀreactionꢀhaveꢀbeenꢀinvestigatedꢀbyꢀphotoluminescenceꢀspectroscopyꢀandꢀquenchingꢀex‐
periments.ꢀ Aꢀ possibleꢀ photocatalyticꢀ degradationꢀ mechanismꢀ ofꢀ acidꢀ redꢀ Gꢀ dyeꢀ byꢀ theꢀ
Silverꢀoxideꢀ
Titaniumꢀdioxideꢀ
Sepioliteꢀ
Heterostructureꢀ
Photocatalysisꢀ
AcidꢀredꢀGꢀ
2 2
Ag O‐TiO /sepioliteꢀcompositeꢀisꢀalsoꢀdiscussed.ꢀ
©ꢀ2015,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
Photocatalyticꢀmechanism
1.ꢀ ꢀ Introductionꢀ
photocatalyticꢀ activityꢀ forꢀ decomposingꢀ formaldehydeꢀ underꢀ
sunlightꢀ irradiationꢀ thanꢀ didꢀ pureꢀ TiO2ꢀandꢀ AgAlO
attributedꢀ toꢀ theꢀ heterojunctionꢀ providingꢀ aꢀ matchingꢀ energyꢀ
bandꢀstructure.ꢀLeeꢀetꢀal.ꢀ[18]ꢀfoundꢀthatꢀTiO /CuOꢀnanofiberꢀ
exhibitedꢀ highꢀ photocatalyticꢀ propertiesꢀ forꢀ degradingꢀ andꢀ
cleaningꢀ theꢀ organicsꢀ producedꢀ fromꢀ dyeꢀ wastewater,ꢀ whichꢀ
canꢀbeꢀascribedꢀtoꢀtheꢀhighꢀquantumꢀefficiency.ꢀ ꢀ
2
.ꢀ Thisꢀ wasꢀ
Photocatalysisꢀtechnologyꢀisꢀconsideredꢀaꢀpromisingꢀmeth‐
odꢀforꢀairꢀandꢀsewageꢀpurificationꢀbecauseꢀitꢀisꢀefficient,ꢀeco‐
nomical,ꢀ andꢀ environmentallyꢀ viableꢀ [1–6].ꢀ Titaniumꢀ dioxideꢀ
2
(
TiO
nontoxicity,ꢀ highꢀ chemicalꢀ stability,ꢀ andꢀ lowꢀ costꢀ [7–9].ꢀ How‐
ever,ꢀ TiO ꢀ canꢀ onlyꢀ exhibitꢀ photocatalyticꢀ activityꢀ underꢀ UVꢀ
2
)ꢀ hasꢀ alsoꢀ receivedꢀ increasedꢀ attentionꢀ becauseꢀ ofꢀ itsꢀ
2
Inꢀaddition,ꢀresearchersꢀhaveꢀfoundꢀthatꢀsilverꢀoxideꢀ(Ag O)ꢀ
2
light.ꢀ Furthermore,ꢀ itsꢀ poorꢀ adsorptionꢀ capacityꢀ andꢀ highꢀ re‐
combinationꢀrateꢀofꢀphotogeneratedꢀelectron‐holeꢀpairsꢀhinderꢀ
itsꢀpracticalꢀapplicationꢀ[10–12].ꢀToꢀresolveꢀthisꢀproblem,ꢀvari‐
ousꢀmethods,ꢀsuchꢀasꢀchemicalꢀmodificationꢀ[13],ꢀmetallizationꢀ
canꢀactꢀasꢀaꢀnovelꢀvisible‐light‐drivenꢀsemiconductorꢀmaterialꢀ
becauseꢀofꢀitsꢀuniqueꢀbandꢀgap,ꢀgoodꢀsensitivityꢀtoꢀlight,ꢀfacileꢀ
preparation,ꢀ andꢀ inexpensiveness,ꢀ meaningꢀ thatꢀ thisꢀ couldꢀ beꢀ
anꢀexcellentꢀcharge‐separationꢀpromoterꢀandꢀbuilt‐inꢀacceptorꢀ
[19–21].ꢀ Agꢀ particlesꢀ areꢀ alsoꢀ usedꢀ asꢀ aꢀ cleaningꢀ agentꢀ toꢀ re‐
moveꢀbacteriaꢀfromꢀcontaminatedꢀwaterꢀ[22–24].ꢀTheoretically,ꢀ
[14],ꢀ andꢀ theꢀ developmentꢀ ofꢀ novelꢀ heterostructureꢀ semicon‐
ductorsꢀ [15,16],ꢀ haveꢀ beenꢀ employedꢀ toꢀ enhanceꢀ theꢀ
charge‐separationꢀefficiency.ꢀForꢀexample,ꢀTangꢀetꢀal.ꢀ[17]ꢀre‐
2
theꢀ conductionꢀ bandꢀ (CB)ꢀ ofꢀ Ag Oꢀ isꢀ moreꢀ negativeꢀ thanꢀ theꢀ
2 2
portedꢀthatꢀtheꢀAg/AlO /TiO ꢀheterojunctionꢀpresentedꢀhigherꢀ
correspondingꢀbandꢀofꢀTiO ,ꢀandꢀtheꢀvalenceꢀbandꢀ(VB)ꢀofꢀTiO ꢀ
2
2
*
ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐27‐87651816;ꢀFax:ꢀ+86‐27‐87887445;ꢀE‐mail:ꢀgkzhang@whut.edu.cnꢀ
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀKeyꢀTechnologyꢀR&DꢀProgramꢀofꢀChinaꢀ(2012BAJ25B02‐03).ꢀ
DOI:ꢀ10.1016/S1872‐2067(15)61015‐4ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ36,ꢀNo.ꢀ12,ꢀDecemberꢀ2015ꢀ ꢀ

2220ꢀ
YuꢀDuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228ꢀ
isꢀmoreꢀpositiveꢀthanꢀthatꢀofꢀAg
gapsꢀandꢀpositionsꢀmightꢀfavorꢀtheꢀformationꢀofꢀAg
2
Oꢀ[25].ꢀ Theirꢀmatchingꢀbandꢀ
calcinedꢀatꢀ100,ꢀ200,ꢀ350,ꢀandꢀ450ꢀ°Cꢀforꢀ30ꢀminꢀunderꢀambientꢀ
conditions.ꢀ Theꢀ resultingꢀ samplesꢀ wereꢀ storedꢀ inꢀ theꢀ darkꢀ inꢀ
theꢀformꢀofꢀfineꢀwhiteꢀpowdersꢀ(<ꢀ400ꢀ°C),ꢀinꢀwhichꢀtheꢀAg Oꢀ
phaseꢀ mayꢀ existꢀ onꢀ theꢀ surfaceꢀ ofꢀ theꢀ TiO /sepioliteꢀ compo‐
sites.ꢀTheꢀcolorꢀofꢀtheꢀAg O‐TiO /sepioliteꢀcompositesꢀchangedꢀ
toꢀ grayꢀ byꢀ increasingꢀ theꢀ calcinationꢀ temperatureꢀ toꢀ 450ꢀ °C,ꢀ
owingꢀ toꢀ theꢀ decompositionꢀ ofꢀ Ag Oꢀ toꢀ metallicꢀ Agꢀ [25].ꢀ Forꢀ
comparisonꢀ andꢀ toꢀ investigateꢀ theꢀ effectꢀ ofꢀ Ag Oꢀ particlesꢀ onꢀ
theꢀ photocatalyticꢀ performanceꢀ ofꢀ sepioliteꢀ clay,ꢀ pureꢀ
Ag O‐TiO ꢀandꢀAg O/sepioliteꢀcompositesꢀwereꢀalsoꢀpreparedꢀ
2
O‐TiO ꢀhet‐
2
erostructures,ꢀ whichꢀ expandsꢀ theꢀ photoabsorptionꢀ rangeꢀ andꢀ
facilitatesꢀtheꢀseparationꢀofꢀphotogeneratedꢀelectronsꢀandꢀholeꢀ
pairsꢀ [26–31].ꢀ However,ꢀ theirꢀ applicationꢀ isꢀ alsoꢀ limitedꢀ byꢀ
weakꢀ adsorptionꢀ andꢀ theꢀ difficultyꢀ inꢀ separatingꢀ themꢀ fromꢀ
wastewater.ꢀ
Sepioliteꢀisꢀ aꢀmicrofibrousꢀ clayꢀmineralꢀconsistingꢀofꢀaꢀ2:1ꢀ
layeredꢀstructureꢀbuiltꢀbyꢀtwoꢀtetrahedralꢀsilicaꢀsheetsꢀwithꢀaꢀ
centralꢀmagnesiaꢀsheetꢀ[32].ꢀItsꢀpeculiarꢀstructuralꢀtunnelsꢀleadꢀ
2
2
2
2
2
2
2
2
2
toꢀinterestingꢀsurfaceꢀpropertiesꢀandꢀhighꢀabsorptionꢀcapacityꢀ
followingꢀtheꢀsameꢀprocedureꢀtoꢀprovideꢀ10%Ag
sepioliteꢀ(200ꢀ°C).ꢀ
2
O‐30%TiO
2
/
ꢀ
ꢀ
[33].ꢀZhangꢀetꢀal.ꢀ[34]studiedꢀbicrystallineꢀTiO
2
ꢀbyꢀsupportingꢀitꢀ
onꢀporousꢀ sepioliteꢀ clayꢀforꢀtheꢀ photocatalyticꢀdegradationꢀofꢀ
gaseousꢀ formaldehyde,ꢀ whereinꢀ theꢀ TiO /sepioliteꢀ showedꢀ aꢀ
higherꢀphotocatalyticꢀactivityꢀthanꢀcommercialꢀDegussaꢀP‐25ꢀorꢀ
bareꢀTiO .ꢀMoreover,ꢀtheꢀlayeredꢀstructureꢀofꢀsepioliteꢀexhibit‐
edꢀhigherꢀphysicochemicalꢀstability.ꢀThus,ꢀsepioliteꢀmayꢀalsoꢀbeꢀ
aꢀgoodꢀsupportꢀforꢀtheꢀAg O‐TiO ꢀheterojunctionꢀcatalyst,ꢀwhichꢀ
2
2.2.ꢀ ꢀ Catalystꢀcharacterizationꢀ
2
X‐rayꢀ diffractionꢀ (XRD,ꢀ Rigakuꢀ D/MAX‐RBꢀ diffractometer,ꢀ
operatingꢀatꢀ40ꢀkVꢀandꢀ50ꢀmAꢀwithꢀCuꢀK ꢀradiation,ꢀλꢀ=ꢀ0.15406ꢀ
nm)ꢀ wasꢀ usedꢀ toꢀ determineꢀ theꢀ structureꢀ andꢀ crystallinityꢀ ofꢀ
theꢀ as‐preparedꢀ samples.ꢀ X‐rayꢀ photoelectronꢀ spectroscopyꢀ
(XPS)ꢀ dataꢀ wereꢀ collectedꢀ usingꢀ anꢀ ESCALABꢀ IIꢀ XPSꢀ systemꢀ
α
2
2
canꢀimproveꢀtheꢀcatalystꢀadsorptionꢀcapacityꢀandꢀcatalystꢀsep‐
aration,ꢀandꢀitsꢀrecyclingꢀfromꢀwastewater.ꢀ
2 2
Inꢀ theꢀ presentꢀ work,ꢀ heterostructureꢀ Ag O‐TiO /sepioliteꢀ
operatingꢀinꢀhybridꢀmode,ꢀwithꢀaꢀmonochromaticꢀMgꢀK ꢀsourceꢀ
α
compositesꢀ wereꢀ synthesizedꢀ byꢀ aꢀ simpleꢀ two‐stepꢀ method.ꢀ
Theirꢀphotocatalyticꢀactivitiesꢀwereꢀinvestigatedꢀbyꢀtheꢀphoto‐
catalyticꢀdegradationꢀofꢀacidꢀredꢀGꢀ(ARG)ꢀaqueousꢀsolutionꢀandꢀ
gaseousꢀformaldehydeꢀunderꢀvisible‐lightꢀirradiationꢀ(λꢀ>ꢀ420ꢀ
nm).ꢀTheꢀstructuralꢀfeaturesꢀofꢀtheꢀcompositesꢀwereꢀanalyzedꢀ
throughꢀsystematicꢀcharacterization,ꢀandꢀtheꢀvisible‐lightꢀpho‐
andꢀaꢀchargeꢀneutralizer.ꢀAllꢀbindingꢀenergiesꢀobtainedꢀbyꢀtheꢀ
XPSꢀspectralꢀanalysisꢀusedꢀtheꢀCꢀ1sꢀpeakꢀatꢀ284.5ꢀeVꢀasꢀaꢀrefer‐
ence.ꢀTheꢀmorphologiesꢀofꢀtheꢀsamplesꢀwereꢀobservedꢀbyꢀscan‐
ningꢀelectronicꢀmicroscopyꢀ(SEM,ꢀJSM5610LV).ꢀTheꢀabsorptionꢀ
edgeꢀ ofꢀ theꢀ samplesꢀ wasꢀ measuredꢀ byꢀ anꢀ ultraviolet‐visibleꢀ
(UV‐vis)ꢀ spectrophotometerꢀ (UV‐2550,ꢀ Shimadzu),ꢀ forꢀ whichꢀ
2 2
tocatalyticꢀmechanismꢀofꢀtheꢀAg O‐TiO /sepioliteꢀcompositesꢀisꢀ
2
theꢀ rawꢀ sepioliteꢀ andꢀ TiO ‐supportedꢀ catalystꢀ samplesꢀ wereꢀ
discussedꢀinꢀdetail.ꢀ
2
usedꢀ asꢀ theꢀ reflectanceꢀ standard.ꢀ Aꢀ N ꢀ adsorption‐desorptionꢀ
isothermꢀ wasꢀ obtainedꢀ atꢀ liquidꢀ nitrogenꢀ temperatureꢀ (196ꢀ
°C)ꢀ usingꢀ aꢀ Quantachromeꢀ AUTOSORB‐1ꢀ nitrogenꢀ adsorptionꢀ
apparatus.ꢀ Theꢀ specificꢀ surfaceꢀ areaꢀ wasꢀ determinedꢀ byꢀ theꢀ
multi‐pointꢀBETꢀmethodꢀandꢀtheꢀporeꢀsizesꢀwereꢀmeasuredꢀbyꢀ
theꢀBJHꢀmethodꢀofꢀadsorption.ꢀTheꢀFourierꢀtransformꢀinfraredꢀ
(FT‐IR)ꢀ spectraꢀ ofꢀ theꢀ chemicalꢀ bondsꢀ onꢀ theꢀ surfaceꢀ ofꢀ theꢀ
samplesꢀ wereꢀ obtainedꢀ usingꢀ aꢀ Thermoꢀ Nicoletꢀ Nexusꢀ spec‐
trometer.ꢀPhotoluminescenceꢀ(PL)ꢀspectraꢀwereꢀrecordedꢀviaꢀaꢀ
fluorescenceꢀspectrophotometerꢀ(RF‐5301PC,ꢀShimadzu)ꢀwithꢀ
anꢀ excitationꢀ wavelengthꢀ ofꢀ 312ꢀ nm,ꢀ whichꢀ isꢀ capableꢀ ofꢀ de‐
2
.ꢀ ꢀ Experimentalꢀ
.1.ꢀ ꢀ Catalystꢀprepartationꢀ
Theꢀ sepioliteꢀ sampleꢀ usedꢀ inꢀ thisꢀ studyꢀ wasꢀ fromꢀ Hunanꢀ
2
Province,ꢀChina.ꢀAllꢀchemicalꢀreagentsꢀwereꢀofꢀanalyticalꢀgradeꢀ
andꢀ usedꢀ withoutꢀ furtherꢀ purification.ꢀ Theꢀ synthesisꢀ ofꢀ
Ag
2
O‐TiO
TiO ꢀsolꢀwasꢀpreparedꢀbyꢀanꢀacid‐catalyzedꢀsol‐gelꢀmethodꢀ
fromꢀaꢀTiCl ꢀprecursorꢀ(SinopharmꢀChemicalꢀReagentꢀCo.,ꢀLtd.,ꢀ
China).ꢀTiCl ꢀ(8ꢀmL)ꢀwasꢀaddedꢀgraduallyꢀtoꢀaꢀHClꢀsolutionꢀ(22ꢀ
wt%)ꢀ underꢀ continuousꢀ stirringꢀ forꢀ 0.5ꢀ hꢀ atꢀ 25ꢀ °C,ꢀ andꢀ thenꢀ
agedꢀforꢀ6ꢀhꢀtoꢀobtainꢀaꢀtransparentꢀTiO ꢀsol.ꢀThen,ꢀtheꢀTiO ꢀsolꢀ
2
/sepioliteꢀcompositeꢀcomprisesꢀtwoꢀmainꢀprocesses.ꢀ
2
•
4
tectingꢀ theꢀ hydroxylꢀ radicalꢀ ( OH)ꢀ duringꢀ theꢀ photocatalyticꢀ
degradationꢀprocess.ꢀ
4
2
2
2.3.ꢀ ꢀ Photocatalyticꢀactivityꢀmeasurementsꢀ
wasꢀaddedꢀdropwiseꢀintoꢀsepioliteꢀpowderꢀsaturatedꢀwithꢀde‐
ionizedꢀwaterꢀ(1ꢀwt%)ꢀunderꢀvigorousꢀstirringꢀforꢀ0.5ꢀhꢀatꢀ70ꢀ
TheꢀphotocatalyticꢀdegradationꢀexperimentsꢀofꢀARGꢀdyeꢀandꢀ
gaseousꢀ formaldehydeꢀ wereꢀ performedꢀ underꢀ visible‐lightꢀ ir‐
radiationꢀatꢀroomꢀtemperature.ꢀAꢀdesiredꢀamountꢀ(0.15ꢀg)ꢀofꢀ
theꢀas‐preparedꢀcatalystꢀwasꢀhomogeneouslyꢀsuspendedꢀinꢀtheꢀ
ARGꢀdyeꢀaqueousꢀsolutionꢀ(100ꢀmg/L)ꢀunderꢀcontinuousꢀstir‐
ringꢀforꢀ30ꢀminꢀinꢀaꢀdarkꢀenvironmentꢀtoꢀestablishꢀtheꢀadsorp‐
tion‐desorptionꢀequilibrium.ꢀTheꢀreactionꢀwasꢀstartedꢀbyꢀdirectꢀ
exposureꢀ toꢀ visible‐lightꢀ irradiationꢀ (300ꢀ Wꢀ Dyꢀ lamp)ꢀ withꢀ aꢀ
420‐nmꢀ cutoffꢀ filter.ꢀ Atꢀ givenꢀ timeꢀ intervalsꢀ ofꢀ illumination,ꢀ
smallꢀaliquotsꢀofꢀtheꢀstirredꢀsuspensionꢀwereꢀdrawnꢀandꢀcen‐
trifugedꢀtoꢀremoveꢀtheꢀphotocatalyst.ꢀTheꢀsupernatantꢀliquorꢀofꢀ
theꢀ ARGꢀ dyeꢀ wasꢀ analyzedꢀ byꢀ UV‐visꢀ spectrophotometryꢀ
(UV751GD,ꢀ China)ꢀ atꢀ itsꢀ maximumꢀ absorptionꢀ wavelengthꢀ
°
C,ꢀbeforeꢀbeingꢀagedꢀforꢀ12ꢀhꢀtoꢀobtainꢀindividualꢀTiO
2
ꢀloadingsꢀ
ofꢀ30ꢀwt%ꢀonꢀtheꢀ sepioliteꢀsupportꢀ (30%TiO /sepiolite).ꢀ Theꢀ
2
resultingꢀ mixedꢀ suspensionsꢀ wereꢀ centrifugedꢀ atꢀ 5000ꢀ r/minꢀ
severalꢀ timesꢀ andꢀ thenꢀ washedꢀ withꢀ deionizedꢀ waterꢀ toꢀ neu‐
−
tralizeꢀ theꢀ supernatantsꢀ untilꢀ noꢀ Cl ꢀ wasꢀ detectedꢀ byꢀ AgNO
3
ꢀ
solution.ꢀ Afterꢀ removingꢀ allꢀ excessiveꢀ chloride,ꢀ theꢀ samplesꢀ
wereꢀdriedꢀatꢀ70ꢀ°Cꢀforꢀ5ꢀh.ꢀ
Ag
impregnationꢀmethod.ꢀTiO
persedꢀinꢀ18.5ꢀmLꢀofꢀAgNO
2
O‐TiO
2
/sepioliteꢀ compositesꢀ wereꢀ synthesizedꢀ viaꢀ anꢀ
/sepioliteꢀpowderꢀ(1.00ꢀg)ꢀwasꢀdis‐
ꢀsolutionꢀ(0.05ꢀmol/L)ꢀtoꢀproduceꢀaꢀ
2
3
suspensionꢀ(Ag/powdersꢀ=ꢀ10ꢀwt%).ꢀAfterꢀstirringꢀinꢀtheꢀdarkꢀ
forꢀ2ꢀh,ꢀtheꢀresultingꢀsuspensionꢀwasꢀdriedꢀatꢀ60ꢀ°Cꢀandꢀthenꢀ

ꢀ
YuꢀDuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228ꢀ
2221ꢀ
(λmax)ꢀofꢀ505ꢀnm.ꢀ
2 2
theꢀ anataseꢀ crystallineꢀ phaseꢀ forꢀ Ag O‐TiO /sepioliteꢀ compo‐
Gaseousꢀ formaldehydeꢀ degradationꢀ wasꢀ conductedꢀ inꢀ aꢀ
sitesꢀcanꢀlikelyꢀbeꢀattributedꢀtoꢀtheꢀstabilizingꢀeffectꢀofꢀtheꢀsilicaꢀ
thatꢀ existsꢀ inꢀ theꢀ sepioliteꢀ frameworkꢀ [32].ꢀ Inꢀ Fig.ꢀ 1(a),ꢀ theꢀ
closedꢀstainlessꢀsteelꢀphotoreactorꢀwithꢀanꢀinnerꢀvolumeꢀofꢀ0.8ꢀ
L.ꢀTheꢀas‐preparedꢀcatalyst,ꢀwithꢀaꢀdosageꢀofꢀ0.15ꢀg,ꢀwasꢀdis‐
persedꢀinꢀaꢀdishꢀofꢀdiameterꢀ70ꢀmm.ꢀThenꢀtheꢀsampleꢀwasꢀsetꢀ
intoꢀ theꢀ gasꢀ photoreactor,ꢀ andꢀ formaldehydeꢀ solutionꢀ (2ꢀ μL)ꢀ
wasꢀinjectedꢀintoꢀtheꢀphotoreactorꢀbyꢀmicrosyringe.ꢀTheꢀreac‐
torꢀwasꢀblownꢀbyꢀaꢀfanꢀforꢀtheꢀformaldehydeꢀtoꢀslowlyꢀvolatilizeꢀ
untilꢀtheꢀinitialꢀconcentrationꢀreachedꢀequilibrium.ꢀAfterꢀsever‐
alꢀ minutes,ꢀ aꢀ 300ꢀ Wꢀ Dyꢀ lampꢀ wasꢀ turnedꢀ onꢀ toꢀ irradiateꢀ theꢀ
photoreactorꢀwithꢀaꢀ420‐nmꢀcutoffꢀfilter.ꢀAꢀ1412ꢀphotoacousticꢀ
fieldꢀgas‐monitorꢀ(InnovaꢀAirTechꢀInstruments,ꢀDenmark)ꢀwasꢀ
appliedꢀ toꢀ detectꢀ theꢀ concentrationꢀ ofꢀ gaseousꢀ formaldehyde,ꢀ
peaksꢀcorrespondingꢀtoꢀtheꢀAg
ble.ꢀToꢀfurtherꢀdemonstrateꢀtheꢀphaseꢀstructuresꢀofꢀtheꢀAgꢀonꢀ
theꢀsurfaceꢀofꢀtheꢀsepiolite,ꢀtheꢀweakꢀdiffractionꢀpeaksꢀofꢀAg Oꢀ
2
Oꢀphaseꢀareꢀnotꢀclearlyꢀdetecta‐
2
atꢀ 2θꢀ =ꢀ 32.7°ꢀ (JCPDSꢀ 12‐0793)ꢀ andꢀ metallicꢀ Agꢀ atꢀ 2θꢀ =ꢀ 44.3°ꢀ
(JCPDSꢀ04‐0783)ꢀwereꢀfurtherꢀdetected,ꢀasꢀshownꢀinꢀFig.ꢀ1(b)ꢀ
andꢀ(c).ꢀTheꢀsamplesꢀobtainedꢀatꢀ200ꢀandꢀ350ꢀ°Cꢀwereꢀfoundꢀtoꢀ
containꢀtheꢀAg
theꢀcalcinationꢀtemperatureꢀwasꢀincreasedꢀtoꢀ450ꢀ°Cꢀ(Fig.ꢀ1(c)),ꢀ
whichꢀcanꢀbeꢀattributedꢀtoꢀtheꢀdecompositionꢀofꢀAg Oꢀ[38].ꢀInꢀ
thisꢀstudy,ꢀTiO ꢀcouldꢀexistꢀasꢀaꢀmixtureꢀofꢀnanosizedꢀanataseꢀ
andꢀ rutileꢀ inꢀ theꢀ composites,ꢀ andꢀ theꢀ formationꢀ ofꢀ theꢀ Ag Oꢀ
2
Oꢀphaseꢀ(Fig.ꢀ1(b)).ꢀMetallicꢀAgꢀwasꢀobservedꢀasꢀ
2
2
andꢀtheꢀmineralizationꢀproductsꢀ(CO
2 2
ꢀandꢀH O)ꢀwereꢀalsoꢀmon‐
2
itored.ꢀTheꢀtestsꢀwereꢀperformedꢀatꢀroomꢀtemperatureꢀ(25ꢀ°C).ꢀ
phaseꢀcouldꢀbeꢀinhibitedꢀbyꢀcontrollingꢀtheꢀcalcinationꢀtemper‐
atureꢀbelowꢀ450ꢀ°C.ꢀ
3.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
XPSꢀwasꢀemployedꢀtoꢀanalyzeꢀtheꢀchemicalꢀstateꢀofꢀtheꢀele‐
mentsꢀ onꢀ theꢀ surfaceꢀ ofꢀ theꢀ Ag
2
O‐TiO /sepioliteꢀ composites,ꢀ
2
3
.1.ꢀ ꢀ Photocatalystꢀcharacterizationꢀ
andꢀtheꢀresultsꢀareꢀshownꢀinꢀFig.ꢀ2(a).ꢀInꢀFig.ꢀ2(b),ꢀtheꢀAgꢀ3dꢀ
regionꢀshowsꢀXPSꢀpeaksꢀwithꢀtwoꢀindividualꢀpeaksꢀatꢀ368.3ꢀandꢀ
374.3ꢀeV,ꢀwhichꢀareꢀassignedꢀtoꢀtheꢀAgꢀ3d5/2ꢀandꢀAgꢀ3d3/2ꢀpeaksꢀ
XRDꢀwasꢀusedꢀtoꢀinvestigateꢀtheꢀcrystalꢀstructureꢀofꢀtheꢀcat‐
alystꢀ particles.ꢀ Fig.ꢀ 1(a)ꢀ showsꢀ theꢀ XRDꢀ patternsꢀ overꢀ aꢀ scanꢀ
rangeꢀ ofꢀ 5°ꢀ toꢀ 70°ꢀ forꢀ theꢀ sepiolite,ꢀ TiO /sepiolite,ꢀ andꢀ
Ag O‐TiO /sepioliteꢀcompositesꢀobtainedꢀatꢀdifferentꢀtempera‐
inꢀAg
2
Oꢀphaseꢀ[39,40],ꢀrespectively.ꢀInꢀFig.ꢀ2(c),ꢀtheꢀTiꢀ2pꢀregionꢀ
2
exhibitsꢀ twoꢀ individualꢀ peaksꢀ atꢀ 458.7ꢀ andꢀ 464.3ꢀ eV,ꢀ whichꢀ
indicateꢀ thatꢀ Ti ꢀ ofꢀ TiO
4+
2
2
2
ꢀ isꢀ theꢀ majorꢀ Tiꢀ speciesꢀ inꢀ theꢀ
tures.ꢀItꢀisꢀfoundꢀthatꢀallꢀsamplesꢀshowꢀtheꢀmainꢀphaseꢀofꢀsepio‐
lite,ꢀforꢀwhichꢀtheꢀdiffractionꢀpeaksꢀatꢀ2θꢀ=ꢀ8.78°,ꢀ12.2°,ꢀ24.8°,ꢀ
andꢀ 26.6°ꢀ areꢀ indexedꢀ toꢀ theꢀ (110),ꢀ (130),ꢀ (231),ꢀ andꢀ (080)ꢀ
planes,ꢀrespectively,ꢀofꢀtheꢀpristineꢀsepioliteꢀ(JCPDSꢀ26‐1226).ꢀ ꢀ
Meanwhile,ꢀ theꢀ intensitiesꢀ ofꢀ theꢀ (130),ꢀ (231),ꢀ andꢀ (080)ꢀ
peaksꢀ ofꢀ theꢀ sepioliteꢀ graduallyꢀ decreasedꢀ byꢀ increasingꢀ theꢀ
calcinationꢀ temperature,ꢀ whichꢀ indicatesꢀ thatꢀ theꢀ layeredꢀ
structureꢀofꢀsepioliteꢀwas,ꢀtoꢀsomeꢀextent,ꢀdestroyedꢀ[35,36].ꢀInꢀ
addition,ꢀtheꢀdiffractionꢀpeaksꢀatꢀ2θꢀ=ꢀ25.3°,ꢀ48.1°,ꢀandꢀ55.1°ꢀareꢀ
indexedꢀtoꢀtheꢀ(101),ꢀ(200),ꢀandꢀ(211)ꢀplanes,ꢀrespectively,ꢀofꢀ
Ag O‐TiO /sepioliteꢀcompositesꢀ[41–43].ꢀInꢀaddition,ꢀitꢀcanꢀbeꢀ
seenꢀ thatꢀ theꢀ bindingꢀ energyꢀ valuesꢀ ofꢀ theꢀ Tiꢀ 2pꢀ regionꢀ areꢀ
slightlyꢀincreased,ꢀwhichꢀisꢀattributedꢀtoꢀtheꢀinteractionꢀofꢀAgꢀ
2
2
ionsꢀwithꢀtheꢀTiO
theꢀOꢀ1sꢀregionꢀwithꢀaꢀbindingꢀenergyꢀofꢀ530.1ꢀeVꢀisꢀassignedꢀtoꢀ
theꢀoxygenꢀinꢀtheꢀTiO ꢀcrystalꢀlatticeꢀ[38,39,43],ꢀwhileꢀtheꢀpeakꢀ
2
ꢀsurfaceꢀ[44,45].ꢀInꢀFig.ꢀ2(d),ꢀtheꢀmainꢀpeakꢀofꢀ
2
atꢀ532.4ꢀeVꢀisꢀassignedꢀtoꢀtheꢀmetal–OHꢀbondsꢀ[46].ꢀTheꢀfor‐
+
mationꢀofꢀsilverꢀoxideꢀisꢀattributedꢀtoꢀtheꢀAg ꢀ ionsꢀ absorbingꢀ
2
oxygenꢀ ionsꢀ originatingꢀ fromꢀ theꢀ TiO ꢀmetalꢀcrystalꢀlatticeꢀorꢀ
fromꢀdispersedꢀ–OHꢀinꢀtheꢀclayꢀ[47].ꢀ
theꢀanataseꢀphaseꢀofꢀTiO
atꢀ 2θꢀ =ꢀ 27.4°ꢀ andꢀ 36.0°ꢀ areꢀ indexedꢀ toꢀ theꢀ (110)ꢀ andꢀ (101)ꢀ
planes,ꢀ respectively,ꢀ ofꢀ theꢀ rutileꢀ phaseꢀ ofꢀ TiO
2
ꢀ(JCPDSꢀ83‐2243),ꢀwhereasꢀtheꢀpeaksꢀ
Theꢀ morphologiesꢀ ofꢀ theꢀ sepiolite,ꢀ TiO
O‐TiO /sepioliteꢀcompositesꢀwereꢀcharacterizedꢀbyꢀSEM.ꢀInꢀ
Fig.ꢀ3(a),ꢀtheꢀsepioliteꢀexhibitsꢀaꢀsmoothꢀandꢀflatꢀsurface,ꢀwhileꢀ
theꢀ TiO /sepioliteꢀ compositeꢀ presentsꢀ aꢀ relativelyꢀ roughꢀ andꢀ
loose‐knitꢀsectionꢀ(Fig.ꢀ3(b)).ꢀFromꢀFig.ꢀ3(c),ꢀitꢀcanꢀbeꢀseenꢀthatꢀ
2
/sepiolite,ꢀ andꢀ
Ag
2
2
2
ꢀ (JCPDSꢀ
ꢀ
7
8‐2485) [37].ꢀ Thereꢀ areꢀ commonlyꢀ twoꢀ naturallyꢀ occurringꢀ
2
phasesꢀ ofꢀ titaniaꢀ (rutileꢀ andꢀ anatase)ꢀ whenꢀ theꢀ calcinationꢀ
temperatureꢀisꢀaboveꢀ400ꢀ°Cꢀ[33],ꢀandꢀtheꢀthermalꢀstabilityꢀofꢀ
2 2
aꢀlargeꢀnumberꢀofꢀtheꢀTiO ꢀandꢀAg Oꢀparticlesꢀassembledꢀonꢀtheꢀ
S
SS
S: Sepiolite
A: Anatase
R: Rutile
(
a)
1)
(2)
(b)
(c)
Ag
2
O
Ag
(6)
(5)
(
A
R
R A
A
A
(
4)
(5)
(
3)
4)
5)
6)
(4)
(
(3)
(
(1)
(
10
20
30
2
40
)
50
60
70
30
31
32
)
33
34 43.5
44.0
44.5
45.0
o
o
o
/(
2/(
2/(
)
Fig.ꢀ1.ꢀ(a)ꢀXRDꢀpatternsꢀofꢀsepioliteꢀ(1),ꢀTiO
2
/sepioliteꢀ(2),ꢀAg
2
O‐TiO
2
/sepioliteꢀ(100ꢀ°C)ꢀ(3),ꢀAg
2
O‐TiO
2
/sepioliteꢀ(200ꢀ°C)ꢀ(4),ꢀAg
2
O‐TiO /sepioliteꢀ
2
(
350ꢀ°C)ꢀ(5),ꢀandꢀAg O‐TiO
typicalꢀsamples.ꢀ
2
2
/sepioliteꢀ(450ꢀ°C)ꢀ(6);ꢀTheꢀcorrespondingꢀenlargedꢀdiffractionꢀareasꢀfromꢀ30°ꢀtoꢀ34°ꢀ(b)ꢀandꢀ43.5°ꢀtoꢀ45°ꢀ(c)ꢀforꢀsomeꢀ

2222ꢀ
YuꢀDuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228ꢀ
(a)
Survey
(b)
Ag 3d
O 1s
368.3
374.3
Ti 2p
Ag 3d
C 1s
Si 2p
1200 1000
800
600
400
200
0
380
376
372
368
364
Binding energy (eV)
Binding energy (eV)
Ti 2p
(c)
(d)
O 1s
458.7
532.4
530.1
464.3
4
68
464
Binding energy (eV)
O‐TiO /sepioliteꢀcompositesꢀ(a)ꢀandꢀhigh‐resolutionꢀXPSꢀspectraꢀofꢀAgꢀ3dꢀregionꢀ(b),ꢀTiꢀ2pꢀregionꢀ(c),ꢀandꢀOꢀ1sꢀregionꢀ(d).
460
456
452
538 536 534 532 530 528 526 524
Binding energy (eV)
Fig.ꢀ2.ꢀXPSꢀspectrumꢀofꢀAg
2
2
(
a)
(b)
(c)
Fig.ꢀ3.ꢀSEMꢀimagesꢀofꢀrawꢀsepioliteꢀ(a),ꢀTiO
2 2 2
/sepioliteꢀ(b),ꢀandꢀAg O‐TiO /sepioliteꢀcompositesꢀ(c).ꢀ
surfaceꢀ ofꢀ theꢀ sepiolite,ꢀ andꢀ theirꢀ shapesꢀ areꢀ quiteꢀ irregular.ꢀ
Theꢀmorphologyꢀofꢀtheꢀsepioliteꢀclayꢀshowsꢀnoꢀobviousꢀdiffer‐
ence,ꢀ whileꢀ theꢀ layeredꢀ structuresꢀ ofꢀ theꢀ mineralꢀ congeriesꢀ
Theꢀ N
2
ꢀ adsorption‐desorptionꢀ isothermꢀ andꢀ poreꢀ sizeꢀ dis‐
tributionꢀcurveꢀofꢀtheꢀAg
areꢀ shownꢀinꢀFig.ꢀ5.ꢀTheꢀBETꢀ surfaceꢀ area,ꢀporeꢀvolume,ꢀandꢀ
averageꢀporeꢀsizeꢀofꢀtheꢀdifferentꢀsamplesꢀareꢀsummarizedꢀinꢀ
2
O‐TiO /sepioliteꢀcompositeꢀ(200ꢀ°C)ꢀ
2
wereꢀ partiallyꢀ destroyedꢀ whenꢀ theꢀ TiO ꢀ nanoparticlesꢀ wereꢀ
2
2
introducedꢀintoꢀtheꢀsepioliteꢀbyꢀtheꢀsol‐gelꢀprocess.ꢀ
Tableꢀ 1.ꢀ Theꢀ surfaceꢀ areaꢀ (60.39ꢀ m /g)ꢀ ofꢀ theꢀ
HRTEMꢀwasꢀusedꢀtoꢀfurtherꢀinvestigateꢀtheꢀphaseꢀstructureꢀ
Ag
2
O‐TiO
2
/sepioliteꢀcompositeꢀpreparedꢀatꢀ200ꢀ°Cꢀisꢀfiveꢀtimesꢀ
2
2 2
ofꢀ theꢀ Ag O‐TiO /sepioliteꢀ composite.ꢀ Fig.ꢀ 4(a)ꢀ andꢀ (b)ꢀ showꢀ
higherꢀthanꢀthatꢀofꢀtheꢀrawꢀsepioliteꢀ(12.21ꢀm /g).ꢀTakingꢀintoꢀ
typicalꢀTEMꢀimagesꢀofꢀtheꢀAg
2
O‐TiO /sepioliteꢀcompositeꢀwithꢀ
2
accountꢀ theꢀ calcinationꢀ temperature,ꢀ Ag
compositesꢀshowꢀaꢀhigherꢀthermalꢀstabilityꢀandꢀaꢀlossꢀofꢀspecif‐
icꢀsurfaceꢀareaꢀofꢀbetweenꢀ15%ꢀandꢀ33%ꢀ[49].ꢀTheꢀN ꢀadsorp‐
tion‐desorptionꢀisothermꢀofꢀtheꢀcompositeꢀseemsꢀtoꢀbeꢀtypeꢀIV,ꢀ
accordingꢀtoꢀtheꢀIUPACꢀclassification,ꢀwhichꢀdemonstratesꢀtheꢀ
presenceꢀofꢀmesoporesꢀ(2–50ꢀnm)ꢀ[26].ꢀTheꢀshapeꢀofꢀtheꢀhys‐
teresisꢀloopsꢀisꢀofꢀtypeꢀH3,ꢀwhichꢀisꢀtheꢀmainꢀfeatureꢀofꢀaꢀmul‐
tiporousꢀstructureꢀ[32,50].ꢀTheꢀcontinuouslyꢀincreasedꢀadsorp‐
2
O‐TiO /sepioliteꢀ
2
aꢀlayeredꢀstructure,ꢀwhichꢀisꢀconsistentꢀwithꢀtheꢀSEMꢀobserva‐
tions.ꢀFig.ꢀ4(c)ꢀandꢀ(d)ꢀshowꢀHRTEMꢀimagesꢀrecordedꢀfromꢀtheꢀ
whiteꢀ framedꢀ areasꢀ indicatedꢀ inꢀ Fig.ꢀ 4(b),ꢀ inꢀ whichꢀ itꢀ canꢀ beꢀ
2
seenꢀ thatꢀ twoꢀ crystalsꢀ ofꢀ Ag
nected,ꢀ andꢀ theꢀ latticeꢀ fringeꢀ spacingꢀ ofꢀ 0.272ꢀ nmꢀ (Fig.ꢀ 4(c))ꢀ
correspondsꢀtoꢀ theꢀ(111)ꢀ crystallographicꢀ planeꢀofꢀ Ag O.ꢀ Theꢀ
2
2
Oꢀ andꢀ TiO ꢀ areꢀ tightlyꢀ intercon‐
2
observedꢀ latticeꢀ spacingsꢀ ofꢀ 0.351ꢀ andꢀ 0.324ꢀ nmꢀ (Fig.ꢀ 4(d))ꢀ
correspondꢀ toꢀ theꢀ (101)ꢀ planeꢀ ofꢀ theꢀ anataseꢀ andꢀ theꢀ (110)ꢀ
planeꢀofꢀtheꢀrutileꢀphase,ꢀrespectively.ꢀTheꢀHRTEMꢀimagesꢀfur‐
therꢀconfirmꢀthatꢀheterostructuresꢀofꢀAg
formedꢀinꢀtheꢀcompositesꢀ[48].ꢀ
tionꢀ branchꢀ atꢀ relativeꢀ pressureꢀ (p/p
capillaryꢀ condensationꢀ ofꢀ N ꢀ moleculesꢀ insideꢀ theꢀ differentꢀ
pore‐sizedꢀstructureꢀ(microporesꢀandꢀmesoporous)ꢀ[50–52].ꢀ
TypicalꢀFT‐IRꢀspectraꢀofꢀsepioliteꢀandꢀtheꢀAg O‐TiO sepio‐
0
ꢀ =ꢀ 0.01–1.0)ꢀ indicatesꢀ
2
2
OꢀandꢀTiO ꢀhaveꢀbeenꢀ
2
2
2
/
ꢀ

ꢀ
YuꢀDuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228ꢀ
Tableꢀ1ꢀ
2223ꢀ
(
a)
(b)
Specificꢀsurfaceꢀareasꢀandꢀporeꢀparametersꢀofꢀsepiolite,ꢀTiO
2
/sepiolite,ꢀ
2 2 2 2
Ag O‐TiO ,ꢀandꢀtheꢀAg O‐TiO /sepioliteꢀcompositesꢀpreparedꢀatꢀdiffer‐
entꢀtemperatures.ꢀ
BETꢀsurfaceꢀ Poreꢀvolumeꢀ Averageꢀporeꢀ
Sampleꢀ
2
3
areaꢀ(m /g)ꢀ (cm /g)ꢀ
sizeꢀ(nm)ꢀ
69.46ꢀ
37.60ꢀ
42.19ꢀ
71.29ꢀ
43.66ꢀ
47.74ꢀ
90.60ꢀ
Sepioliteꢀ
12.21ꢀ
63.21ꢀ
ꢀ 3.13ꢀ
51.21ꢀ
60.39ꢀ
40.44ꢀ
44.99ꢀ
0.06ꢀ
0.10ꢀ
0.01ꢀ
0.09ꢀ
0.10ꢀ
0.07ꢀ
0.07ꢀ
TiO /sepioliteꢀ
2
Ag
2
Ag
2
Ag
2
Ag
2
Ag
2
O‐TiO
O‐TiO
O‐TiO
O‐TiO
O‐TiO
2
2
2
2
2
ꢀ
100 nm
/sepioliteꢀ(100ꢀ°C)
/sepioliteꢀ(200ꢀ°C)
/sepioliteꢀ(350ꢀ°C)
/sepioliteꢀ(450ꢀ°C)
2
0 nm
(
c)
(d)
2
Ag O
r-TiO
2
0.351 nm
byꢀ changesꢀ toꢀ theꢀ chemicalꢀ bondꢀ vibrationꢀ forꢀ TiO ꢀ particlesꢀ
2
insertedꢀintoꢀtheꢀlayerꢀofꢀsepioliteꢀorꢀtheꢀbondingꢀofꢀTi–OHꢀ[58],ꢀ
indicatingꢀthatꢀtheꢀlayeredꢀstructureꢀofꢀsepioliteꢀhasꢀbeenꢀde‐
stroyedꢀduringꢀtheꢀpreparationꢀprocess.ꢀMoreover,ꢀtheꢀcharac‐
teristicꢀbandsꢀofꢀSi–OꢀinꢀtheꢀSi–O–Siꢀgroupsꢀofꢀtheꢀtetrahedralꢀ
TiO
2
a-TiO
.324 nm
2
0
5
nm
Ag
2
O(111)
sheetsꢀ(aroundꢀ 1114,ꢀ1033,ꢀ andꢀ469ꢀcm )ꢀstillꢀexist,ꢀandꢀtheꢀ
−1
5
nm
0.272 nm
−1
newꢀpeakꢀatꢀ908ꢀcm ꢀisꢀcausedꢀbyꢀaꢀTi–O–Hꢀstretchingꢀvibra‐
tion.ꢀ Inꢀ addition,ꢀ theꢀ intensitiesꢀ ofꢀ theꢀ vibrationꢀ modesꢀ atꢀ
Fig.ꢀ4.ꢀTEMꢀ(a,b)ꢀandꢀHRTEMꢀ(c,d)ꢀimagesꢀofꢀtheꢀAg
compositeꢀpreparedꢀatꢀ200ꢀ°C.ꢀ
2
O‐TiO /sepioliteꢀ
2
−1
6
37–1033ꢀcm ꢀareꢀdecreased,ꢀwhichꢀindicatesꢀthatꢀtheꢀorganicꢀ
matterꢀonꢀtheꢀclayꢀwasꢀremovedꢀinꢀtheꢀcalcinationꢀprocess.ꢀTheꢀ
FT‐IRꢀspectrumꢀofꢀtheꢀrecoveredꢀcompositeꢀdoesꢀnotꢀshowꢀtheꢀ
characteristicꢀpeakꢀofꢀARGꢀdye,ꢀwhichꢀconfirmsꢀthatꢀotherꢀthanꢀ
thatꢀwhichꢀwasꢀadsorbedꢀbyꢀtheꢀcomposite,ꢀtheꢀARGꢀwasꢀde‐
gradedꢀcompletelyꢀbyꢀtheꢀphotocatalysis.ꢀMeanwhile,ꢀtheꢀresultꢀ
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
0
. .1 .10
.0.0
.0.0
.0.0
.0.0
0
0
0
0
0
0
0 8
8
0 6
6
0 4
4
alsoꢀindicatesꢀthatꢀtheꢀAg
2
O‐TiO /sepioliteꢀcompositeꢀhasꢀgoodꢀ
2
0 2
2
stability.ꢀ
0.00
0.00
Theꢀ UV‐visꢀ diffuseꢀ reflectanceꢀ spectraꢀ ofꢀ sepiolite,ꢀ TiO
O,ꢀ TiO /sepiolite,ꢀ andꢀ Ag O‐TiO /sepioliteꢀ compositeꢀ areꢀ
shownꢀinꢀFig.ꢀ7.ꢀTheꢀabsorptionꢀedgeꢀofꢀtheꢀAg O‐TiO /sepioliteꢀ
compositeꢀ tendsꢀ toꢀ red‐shiftꢀ comparedꢀ withꢀ thatꢀ ofꢀ theꢀ
TiO /sepioliteꢀ sample.ꢀ Theꢀ bandꢀ gapsꢀ ofꢀ pureꢀ TiO ꢀ andꢀ pureꢀ
Oꢀ areꢀ calculatedꢀ toꢀ beꢀ 2.9ꢀ andꢀ 1.0ꢀ eV,ꢀ respectively.ꢀ Theꢀ
O‐TiO /sepioliteꢀ compositeꢀ exhibitedꢀ enhancedꢀ photoab‐
2
,ꢀ
0
10
10
20
30
30
40
40
0
20
Pore diameter (nm)
Ag
2
2
2
2
Pore diameter (nm)
2
2
2
2
Ag
Ag
2
2
0
.0
0.2
0.4
Relative pressure (p/p
ꢀ adsorption‐desorptionꢀ isothermꢀ ofꢀ theꢀ Ag
0.6
0.8
1.0
2
0
)
sorptionꢀfromꢀtheꢀUVꢀlightꢀregionꢀtoꢀtheꢀvisible‐lightꢀregionꢀinꢀ
theꢀrangeꢀ370–430ꢀnm.ꢀTheꢀresultsꢀindicateꢀthatꢀtheꢀAg Oꢀna‐
Fig.ꢀ 5.ꢀ N
2
2
O‐TiO /sepioliteꢀ
2
2
compositeꢀpreparedꢀatꢀ200ꢀ°C.ꢀTheꢀinsetꢀisꢀtheꢀcorrespondingꢀporeꢀsize
distribution.ꢀ
(1)
430
1
637
liteꢀ compositeꢀ beforeꢀ andꢀ afterꢀ photocatalyticꢀ degradationꢀ ofꢀ
ARGꢀdyeꢀareꢀillustratedꢀinꢀFig.ꢀ6.ꢀTheꢀbandsꢀobservedꢀatꢀ3668ꢀ
1
114
3
668
−1
3435
(2)
(3)
cm ꢀcanꢀbeꢀattributedꢀtoꢀtheꢀstretchingꢀvibrationsꢀofꢀhydroxylꢀ
groupsꢀ(Mg OH)ꢀandꢀwaterꢀmoleculesꢀboundꢀtoꢀtheꢀoctahedralꢀ
sheetsꢀofꢀMgꢀionsꢀinꢀtheꢀsepioliteꢀclayꢀ[53–55].ꢀTheꢀbandsꢀbe‐
1
631
637
3
469
1
033
3
668
−1
tweenꢀ 3435ꢀ andꢀ 1637ꢀ cm ꢀ canꢀ beꢀ assignedꢀ toꢀ theꢀ O–Hꢀ
stretchingꢀmodeꢀandꢀtheꢀH–O–Hꢀbendingꢀmodeꢀfromꢀtheꢀinter‐
beddedꢀwaterꢀmoleculeꢀofꢀtheꢀclayꢀ[37].ꢀTheꢀbandsꢀatꢀ1114ꢀandꢀ
3424
1114 908
1
635
633
469
1
033
−
1
1
033ꢀ cm ꢀ areꢀ dueꢀ toꢀ theꢀ stretchingꢀ ofꢀ Si–Oꢀ inꢀ theꢀ Si–O–Siꢀ
3
668
3446
−1
1114
groupsꢀ ofꢀ theꢀ tetrahedralꢀ sheet,ꢀ andꢀ theꢀ peakꢀ atꢀ 637ꢀ cm ꢀ isꢀ
assignedꢀ toꢀ OHꢀ bendingꢀ vibrationsꢀ [56].ꢀ Asꢀ reported,ꢀ theꢀ
Si–O–Alꢀ (octahedral)ꢀ bendingꢀ vibrationsꢀ areꢀ presentꢀ atꢀ 469ꢀ
913
633469
1
008
4000 3500 3000 2500 2000 1500 1000
500

1
−1
Wavenumber (cm )
cm ꢀ[57].ꢀAsꢀshownꢀinꢀFig.ꢀ6(b),ꢀtheꢀdisappearanceꢀofꢀtheꢀbandꢀ
−
1
atꢀ430ꢀcm ꢀisꢀassignedꢀtoꢀSi–O–Siꢀbendingꢀvibrationsꢀ[54],ꢀandꢀ
Fig.ꢀ6.ꢀFT‐IRꢀspectraꢀofꢀsepioliteꢀ(1)ꢀandꢀtheꢀAg O‐TiO /sepioliteꢀcom‐
positeꢀbeforeꢀ(2)ꢀandꢀafterꢀ(3)ꢀphotocatalyticꢀreaction.ꢀ
2
2
−1
theꢀshiftꢀofꢀtheꢀbandsꢀatꢀ3424ꢀandꢀ1631ꢀcm ꢀmightꢀbeꢀcausedꢀ

2224ꢀ
YuꢀDuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228ꢀ
0
0
0
.12
.10
.08
3
.0
.5
2.0
.5
1.0
.5
2.1
1.8
1.5
1.2
0.9
0.6
0.3
0.0
Sepiolite
TiO /sepiolite
Ag O-TiO /sepiolite
TiO
Ag
2
2
2
2
2
1
TiO
Ag
2
2
O
2
O
0
0.06
1
.0
2
.9
0.0
0
1
2
3
4
5
6
0.04
0.02
0.00
hv (eV)
100
200
350
450
o
Calcination temperature ( C)
Fig.ꢀ9.ꢀComparisonꢀofꢀapparentꢀrateꢀconstantsꢀforꢀtheꢀAg
2
O‐TiO /sepio‐
2
3
00
400
500
Wavelength (nm)
Fig.ꢀ 7.ꢀ UV‐visꢀ diffuseꢀ reflectanceꢀ spectraꢀ ofꢀ sepiolite,ꢀ TiO
TiO /sepiolite,ꢀandꢀAg O‐TiO /sepioliteꢀcomposite.ꢀ
600
700
800
liteꢀcatalystsꢀcalcinedꢀatꢀdifferentꢀtemperaturesꢀforꢀtheꢀdegradationꢀofꢀ
ARGꢀsolution.ꢀ
2
,ꢀ Ag O,ꢀ
2
2
2
2
ln(C
0
/C)ꢀ=ꢀkt.ꢀFig.ꢀ9ꢀshowsꢀtheꢀcomparisonꢀofꢀtheꢀapparentꢀrateꢀ
constantsꢀ ofꢀ theꢀ Ag
2
O‐TiO /sepioliteꢀ compositesꢀ atꢀ differentꢀ
2
noparticlesꢀloadedꢀontoꢀtheꢀTiO
gapꢀ forꢀ photocatalyticꢀ decompositionꢀ ofꢀ organicꢀ pollutantsꢀ inꢀ
theꢀvisible‐lightꢀregion.ꢀ
2
/sepioliteꢀhaveꢀaꢀsuitableꢀbandꢀ
calcinedꢀtemperaturesꢀforꢀtheꢀdegradationꢀofꢀARGꢀsolution.ꢀTheꢀ
kꢀvaluesꢀforꢀtheꢀARGꢀdecompositionꢀbyꢀtheꢀcatalystsꢀcalcinedꢀatꢀ
100,ꢀ200,ꢀ 350,ꢀ andꢀ450ꢀ °Cꢀ areꢀ0.064,ꢀ0.104,ꢀ0.048,ꢀandꢀ 0.020ꢀ
−1
min ,ꢀrespectively.ꢀFig.ꢀ10ꢀshowsꢀtheꢀphotocatalyticꢀactivitiesꢀ
ofꢀ theꢀ samplesꢀ withꢀ differentꢀ amountsꢀ ofꢀ Ag Oꢀ underꢀ visi‐
ble‐lightꢀirradiation.ꢀItꢀisꢀclearlyꢀshownꢀthatꢀtheꢀsamplesꢀwithꢀaꢀ
contentꢀ ofꢀ Ag Oꢀ fromꢀ 2%ꢀ toꢀ 10%ꢀ exhibitedꢀ enhancedꢀ photo‐
catalyticꢀactivity.ꢀHowever,ꢀwhenꢀtheꢀcontentꢀofꢀAg Oꢀwasꢀfur‐
therꢀincreasedꢀtoꢀ15%,ꢀnoꢀfurtherꢀenhancementꢀofꢀARGꢀdegra‐
dationꢀcanꢀbeꢀobserved.ꢀHence,ꢀwhenꢀtheꢀcontentꢀofꢀAg Oꢀwasꢀ
increasedꢀ toꢀ 10%,ꢀ aꢀ heterostructureꢀ ofꢀ Ag Oꢀ andꢀ TiO ꢀ wasꢀ
3.2.ꢀ ꢀ PhotocatalyticꢀactivityꢀofꢀAg
2 2
O‐TiO /sepioliteꢀcompositeꢀ
2
Theꢀ photocatalyticꢀ activitiesꢀ ofꢀ theꢀ Ag
compositesꢀ wereꢀ evaluatedꢀ byꢀ photocatalyticꢀ degradationꢀ ofꢀ
ARGꢀdyeꢀsolutionꢀandꢀgaseousꢀformaldehydeꢀunderꢀvisible‐lightꢀ
2
O‐TiO /sepioliteꢀ
2
2
2
irradiation.ꢀAsꢀshownꢀinꢀFig.ꢀ8,ꢀitꢀisꢀclearꢀthatꢀtheꢀTiO
compositesꢀ showedꢀlittleꢀ photocatalyticꢀ performance.ꢀHowev‐
er,ꢀ afterꢀ coatingꢀ Ag Oꢀ nanoparticles,ꢀ theꢀ Ag O‐TiO /sepioliteꢀ
2
/sepioliteꢀ
2
2
2
2
2
2
formedꢀonꢀtheꢀsurfaceꢀofꢀsepiolite,ꢀwhichꢀmadeꢀtheꢀphotocata‐
lyticꢀprocessꢀmoreꢀefficient.ꢀ
Fig.ꢀ11ꢀ displaysꢀtheꢀ photocatalyticꢀdegradationꢀofꢀtheꢀ ARGꢀ
solutionꢀ byꢀ theꢀ differentꢀ photocatalysts.ꢀ Itꢀ isꢀ clearꢀ thatꢀ theꢀ
compositesꢀ showedꢀ anꢀ obviouslyꢀ enhancedꢀ photocatalyticꢀ ac‐
tivityꢀandꢀARGꢀwasꢀcompletelyꢀdecomposedꢀwithꢀanꢀincreaseꢀinꢀ
irradiationꢀtime.ꢀSpecifically,ꢀwhenꢀtheꢀcalcinationꢀtemperatureꢀ
isꢀ 200ꢀ °C,ꢀ theꢀ obtainedꢀ Ag
superiorꢀphotocatalyticꢀ activityꢀandꢀtheꢀconcentrationꢀofꢀARGꢀ
wasꢀdecreasedꢀbyꢀ98%ꢀafterꢀ40ꢀmin,ꢀwhereasꢀonlyꢀaboutꢀ24%ꢀ
2
O‐TiO
2
/sepioliteꢀ compositeꢀ showsꢀ
Ag
catalyticꢀ activityꢀ ofꢀ theꢀ systemsꢀ studied.ꢀ ARGꢀ isꢀ almostꢀ com‐
pletelyꢀdegradedꢀafterꢀ40ꢀminꢀirradiationꢀoverꢀAg O‐TiO sepi‐
2
O‐TiO /sepioliteꢀ compositeꢀ exhibitedꢀ theꢀ highestꢀ photo‐
2
2
2
/
ꢀ
ofꢀARGꢀcouldꢀbeꢀremovedꢀoverꢀtheꢀTiO
2
/sepioliteꢀafterꢀ40ꢀminꢀ
oliteꢀunderꢀvisibleꢀlight,ꢀwhereasꢀonlyꢀaboutꢀ7%ꢀofꢀARGꢀcouldꢀ
beꢀ removedꢀ overꢀ P‐25,ꢀ 11%ꢀ overꢀ pureꢀ sepiolite,ꢀ 24%ꢀ overꢀ
irradiation.ꢀFurthermore,ꢀtheꢀphotocatalyticꢀdegradationꢀofꢀtheꢀ
ARGꢀsolutionꢀfollowedꢀaꢀpseudo‐first‐orderꢀreactionꢀrateꢀ[59].ꢀ
TiO
2
/sepiolite,ꢀ62%ꢀoverꢀTiO
2
‐Ag
2
O,ꢀandꢀ87%ꢀoverꢀAg
2
O/
ꢀ
sepi‐
−1
Thus,ꢀ theꢀ rateꢀ constantꢀ (k,ꢀ min )ꢀ ofꢀ theꢀ ARGꢀ decompositionꢀ
oliteꢀ afterꢀ 40ꢀ minꢀ irradiation.ꢀ Therefore,ꢀ itꢀ isꢀ possibleꢀ thatꢀ aꢀ
2 2
overꢀ Ag O‐TiO /sepioliteꢀ compositesꢀ canꢀ beꢀ estimatedꢀ byꢀ
steadyꢀsystemꢀisꢀformedꢀbetweenꢀAg
2
OꢀandꢀTiO ꢀnanoparticlesꢀ
2
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
Light off
0% Ag
2
O
0.6
0.4
0.2
0.0
2% Ag O
2
2
5% Ag O
2
TiO /sepiolite
o
10% Ag O
1
2
3
4
00 C
2
o
15% Ag O
00 C
2
o
50 C
o
50 C
Light off Light on
-
20
-10
0
10
20
30
40
-20
-10
0
10
Irradiation time (min)
Fig.ꢀ10.ꢀVisible‐lightꢀphotocatalyticꢀdegradationꢀofꢀARGꢀbyꢀAg
sepioliteꢀcatalystsꢀwithꢀdifferentꢀAg Oꢀcontents.ꢀ
20
30
40
Irradiation time (min)
Fig.ꢀ 8.ꢀ Photocatalyticꢀ degradationꢀ ofꢀ ARGꢀ byꢀ TiO
Ag O‐TiO /sepioliteꢀcatalystsꢀobtainedꢀatꢀdifferentꢀtemperaturesꢀunder
visible‐lightꢀirradiation.ꢀ
2
/sepioliteꢀ andꢀ theꢀ
2
O‐TiO /
2
2
2
2

ꢀ
YuꢀDuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228ꢀ
2225ꢀ
1
60
140
20
100
2
2
2
60
40
20
1
0
0
0
0
0
.0
.8
.6
.4
.2
Formaldehyde
(with catalyst)
1
Light off
2
CO (with catalyst)
200
80
80
1
P-25
Sepiolite
TiO /sepiolite
Ag O/sepiolite
Ag O-TiO
Ag O-TiO
Light on
60
40
20
0
160
140
120
2
2
2
2
CO
2
(without catalyst)
2
2
/sepiolite
.0
-
100
30
-20
-10
0
10
20
30
40
0
60
120
180
240
300
Irradiation time (min)
Time (min)
Fig.ꢀ 11.ꢀ Visible‐lightꢀ photocatalyticꢀ degradationꢀ ofꢀ ARGꢀ solutionꢀ byꢀ
differentꢀsamples.ꢀ
Fig.ꢀ12.ꢀVisible‐lightꢀphotocatalyticꢀdegradationꢀofꢀformaldehydeꢀwithꢀ
andꢀwithoutꢀAg O‐TiO /sepioliteꢀcatalyst.ꢀ
2
2
•
basedꢀonꢀmultiphaseꢀheterostructures,ꢀwhichꢀexistꢀinꢀthisꢀcoor‐
dinationꢀtoꢀimproveꢀtheꢀphotocatalyticꢀactivitiesꢀofꢀtheꢀcompo‐
sites.ꢀ Formaldehyde,ꢀ whichꢀ isꢀ aꢀ typicalꢀ volatileꢀ organicꢀ com‐
pound,ꢀ wasꢀ selectedꢀ toꢀ furtherꢀ evaluateꢀ theꢀ photocatalyticꢀ
niqueꢀ wasꢀ conductedꢀ toꢀ detectꢀ theꢀ formationꢀ ofꢀ OH.ꢀ Scaven‐
gersꢀ wereꢀ alsoꢀ employedꢀ toꢀ determineꢀ theꢀ oxidativeꢀ speciesꢀ
duringꢀtheꢀphotocatalyticꢀdegradationꢀprocess.ꢀAsꢀshownꢀinꢀFig.ꢀ
13(a),ꢀtheꢀintensityꢀofꢀtheꢀpeaksꢀincreasedꢀslightlyꢀwithꢀanꢀin‐
•
2 2
propertiesꢀofꢀtheꢀAg O‐TiO /sepioliteꢀcomposites.ꢀ ꢀ
creaseꢀinꢀtheꢀilluminationꢀtime,ꢀindicatingꢀthatꢀ OHꢀwasꢀnotꢀtheꢀ
Fig.ꢀ 12ꢀ showsꢀ theꢀ photocatalyticꢀ degradationꢀ ofꢀ gaseousꢀ
formaldehydeꢀunderꢀvisible‐lightꢀirradiation.ꢀTheꢀconcentrationꢀ
ofꢀ formaldehydeꢀ inꢀ airꢀ wasꢀ reducedꢀ andꢀ theꢀ decompositionꢀ
dominantꢀ speciesꢀ forꢀ theꢀ degradationꢀ ofꢀ ARGꢀ solution.ꢀ Fromꢀ
•
Fig.ꢀ 13(b),ꢀ OHꢀ radicalsꢀ trappingꢀ experimentsꢀ (IPA)ꢀ furtherꢀ
•
determineꢀthatꢀtheꢀ OHꢀwasꢀnotꢀtheꢀmainꢀactiveꢀspeciesꢀinꢀtheꢀ
+
2
productꢀofꢀCO ꢀgasꢀwasꢀgraduallyꢀincreasedꢀwithꢀanꢀincreaseꢀinꢀ
photocatalyticꢀprocess.ꢀKIꢀwasꢀusedꢀasꢀtheꢀscavengerꢀofꢀh ꢀandꢀ
•OH,ꢀsodiumꢀoxalateꢀ(Na
zoquinoneꢀ(BQ)ꢀasꢀtheꢀscavengerꢀofꢀO
theꢀKIꢀandꢀNa ꢀhadꢀsignificantꢀeffectsꢀonꢀtheꢀphotocatalyticꢀ
O‐TiO /sepioliteꢀcomposite,ꢀwhichꢀindicatesꢀ
O
)ꢀasꢀtheꢀscavengerꢀofꢀh ,ꢀandꢀben‐
+
theꢀirradiationꢀtime.ꢀMeanwhile,ꢀFig.ꢀ12ꢀalsoꢀshowsꢀtheꢀresultsꢀ
ofꢀaꢀblankꢀcontrastꢀexperimentꢀforꢀgasꢀformaldehydeꢀexposedꢀ
toꢀvisibleꢀlightꢀwithoutꢀcatalyst,ꢀimplyingꢀthatꢀtheꢀcatalystꢀwasꢀ
criticalꢀforꢀtheꢀdegradationꢀofꢀgaseousꢀformaldehydeꢀtoꢀoccur.ꢀ
2 2
C
4
•−ꢀ[60].ꢀItꢀcanꢀbeꢀseenꢀthatꢀ
2
2 2 4
C O
activityꢀofꢀtheꢀAg
thatꢀtheꢀh ꢀisꢀoneꢀofꢀtheꢀmainꢀactiveꢀspeciesꢀinꢀtheꢀphotocatalyt‐
icꢀsystem.ꢀInꢀtheꢀpresenceꢀofꢀBQ,ꢀtheꢀdegradationꢀefficiencyꢀofꢀ
2
2
+
2 2
Theseꢀ resultsꢀ suggestꢀ thatꢀ theꢀ Ag O‐TiO /sepioliteꢀ compositeꢀ
alsoꢀexhibitsꢀrelativelyꢀhighꢀphotocatalyticꢀactivityꢀforꢀtheꢀdeg‐
radationꢀofꢀgaseousꢀformaldehydeꢀunderꢀvisible‐lightꢀillumina‐
tion.ꢀ
Ag
isꢀalsoꢀoneꢀofꢀtheꢀmajorꢀactiveꢀspeciesꢀinꢀtheꢀphotocatalyticꢀsys‐
tem.ꢀO
•−ꢀcouldꢀbeꢀgeneratedꢀbyꢀtheꢀadsorbedꢀoxygenꢀmoleculeꢀ
2
O‐TiO
2
/
ꢀ
sepioliteꢀlargelyꢀdecreased,ꢀwhichꢀsuggestsꢀthatꢀO
2
•−ꢀ
2
3
.3.ꢀ ꢀ Photocatalyticꢀmechanismꢀ
onꢀtheꢀ surfaceꢀ ofꢀtheꢀcatalystꢀ capturingꢀactiveꢀ electronsꢀ[26].ꢀ
+
•−ꢀradicalsꢀcouldꢀplayꢀanꢀimportantꢀroleꢀinꢀ
Thus,ꢀoxidativeꢀh /O
2
•
+
•−)ꢀareꢀveryꢀim‐
Photoinducedꢀactiveꢀspeciesꢀ( OH,ꢀh ,ꢀandꢀO
2
theꢀphotocatalyticꢀsolutionꢀunderꢀvisible‐lightꢀirradiationꢀandꢀinꢀ
portantꢀforꢀtheꢀmineralizationꢀofꢀorganicꢀcontaminants.ꢀThere‐
fore,ꢀ theꢀ terephthalicꢀ acidꢀ photoluminescenceꢀ (TAPL)ꢀ tech‐
theꢀ photocatalyticꢀ ARGꢀ degradationꢀ abilityꢀ ofꢀ theꢀ compositeꢀ
capturingꢀtheꢀreactiveꢀspeciesꢀh ,ꢀ OH,ꢀandꢀ O
–.ꢀ
+
•
•
2
40
30
20
10
0
(a)
(b)
1
.0
0.8
0.6
5
4
0 min
0 min
Light off
30 min
2
1
0 min
0 min
KI
Na
BQ
IPA
0.4
0.2
0.0
2
C
2
O
4
0
min
No quenchers
3
60
390
420
450
Wavelength (nm)
Fig.ꢀ13.ꢀ(a)ꢀ OHꢀtrappingꢀPLꢀspectraꢀofꢀterephthalicꢀacidꢀ(TA)ꢀsolutionꢀinꢀtheꢀpresenceꢀofꢀtheꢀAg
dationꢀofꢀARGꢀoverꢀtheꢀAg O‐TiO /sepioliteꢀwithꢀandꢀwithoutꢀtheꢀquenchers.
480
510
540
570
-20
-10
0
10
Irradiation time (min)
O‐TiO /sepioliteꢀcomposite;ꢀ(b)ꢀPhotocatalyticꢀdegra‐
20
30
40
•
2
2
2
2

2226ꢀ
YuꢀDuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228ꢀ
substrateꢀ forꢀ Ag
activeꢀsitesꢀandꢀenhanceꢀtheꢀadsorptionꢀproperties.ꢀInꢀaddition,ꢀ
2
O‐TiO ꢀ heterostructureꢀ couldꢀ provideꢀ moreꢀ
2
Organic dye
Products
O2
e- e- e- e-
CB
+
•−ꢀradicalsꢀcouldꢀbeꢀtheꢀmainꢀactiveꢀspeciesꢀduringꢀ
theꢀh ꢀandꢀO
2
·
O2¯
theꢀ photo‐oxidationꢀ process.ꢀ Thisꢀ resultꢀ mayꢀ provideꢀ aꢀ newꢀ
strategyꢀforꢀtheꢀdesignꢀandꢀdevelopmentꢀofꢀhigh‐performanceꢀ
visible‐lightꢀphotocatalysts.ꢀ
Ag O
E
g
= 1.0 eV
2
e- e- e- e-
CB
Visible light
Organic dye
Visible light
h+ h+ h+ h+
VB
Referencesꢀ
E = 2.9 eV
TiO2
g
Products
[1] WangꢀH,ꢀYuanꢀXꢀZ,ꢀWuꢀY,ꢀZengꢀGꢀM,ꢀChenꢀXꢀH,ꢀLengꢀLꢀJ,ꢀWuꢀZꢀB,ꢀ
JiangꢀLꢀB,ꢀLiꢀH.ꢀJꢀHazardꢀMater,ꢀ2015,ꢀ286:ꢀ187ꢀ
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[2] LiuꢀJ,ꢀZhangꢀGꢀK.ꢀApplꢀSurfꢀSci,ꢀ2014,ꢀ319:ꢀ291ꢀ
[
[
[
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VB
Fig.ꢀ 14.ꢀ Proposedꢀ photocatalyticꢀ mechanismꢀ ofꢀ Ag
catalystsꢀforꢀtheꢀdegradationꢀofꢀARGꢀsolutionꢀunderꢀirradiationꢀofꢀvisi‐
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2
O‐TiO /sepioliteꢀ
2
2012,ꢀ17:ꢀ200ꢀ
[
[
[
[
6] LiuꢀJ,ꢀZhangꢀGꢀK.ꢀPhysꢀChemꢀChemꢀPhys,ꢀ2014,ꢀ16:ꢀ8178ꢀ
7] HeꢀF,ꢀMaꢀF,ꢀLiꢀT,ꢀLiꢀGꢀX.ꢀChinꢀJꢀCatal,ꢀ2013,ꢀ34:ꢀ2263ꢀ
8] YangꢀYꢀQ,ꢀZhangꢀGꢀK,ꢀXuꢀW.ꢀJꢀColloidꢀInterfaceꢀSci,ꢀ2012,ꢀ376:ꢀ217ꢀ
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Theꢀ enhancedꢀ photocatalyticꢀ mechanismꢀ ofꢀ Ag
pioliteꢀheterostructureꢀisꢀpresentedꢀinꢀFig.ꢀ14.ꢀTheꢀhighꢀphoto‐
catalyticꢀ activityꢀ ofꢀ theꢀ Ag O‐TiO /sepioliteꢀ compositeꢀ canꢀ beꢀ
attributedꢀtoꢀAg O‐TiO ꢀheterostructureꢀbeingꢀinꢀtheꢀcompositeꢀ
andꢀtheꢀporousꢀstructureꢀofꢀsepiolite.ꢀUnderꢀvisible‐lightꢀirradi‐
2
O‐TiO
2
/
ꢀ
se‐
[
10] CaoꢀXꢀY,ꢀOdaꢀY,ꢀShiraishiꢀF.ꢀChemꢀEngꢀJ,ꢀ2010,ꢀ156:ꢀ98ꢀ
11] PelaezꢀM,ꢀdeꢀlaꢀCruzꢀAꢀA,ꢀStathatosꢀE,ꢀFalarasꢀP,ꢀDionysiouꢀDꢀD.ꢀ
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[12] ArañaꢀJ,ꢀPeñaꢀAlonsoꢀA,ꢀDoñaꢀRodríguezꢀJꢀM,ꢀHerreraꢀMeliánꢀJꢀA,ꢀ
GonzálezꢀDíazꢀO,ꢀPérezꢀPeñaꢀJ.ꢀApplꢀCatalꢀB,ꢀ2008,ꢀ78:ꢀ355ꢀ
2
2
[
2
2
+
−
ation,ꢀAg
theirꢀnarrowꢀbandꢀgap.ꢀMeanwhile,ꢀAg
chargesꢀ thatꢀ canꢀ easilyꢀ adsorbꢀ ontoꢀ positivelyꢀ chargedꢀ TiO
nanoparticlesꢀ[48,61,62].ꢀInꢀthisꢀcase,ꢀtheꢀphotogeneratedꢀelec‐
tronsꢀonꢀtheꢀCBꢀofꢀAg OꢀcanꢀtransferꢀintoꢀtheꢀCBꢀofꢀTiO ꢀandꢀtheꢀ
photogeneratedꢀ holesꢀ gatherꢀ inꢀ theꢀ VBꢀ ofꢀ Ag O.ꢀ Finally,ꢀ theꢀ
2
Oꢀnanoparticlesꢀcanꢀbeꢀexcitedꢀtoꢀh ꢀandꢀe ꢀbecauseꢀofꢀ
2
Oꢀhasꢀexcessiveꢀnegativeꢀ
[13] HeꢀX,ꢀTangꢀAꢀD,ꢀYangꢀHꢀM,ꢀOuyangꢀJ.ꢀApplꢀClayꢀSci,ꢀ2011,ꢀ53:ꢀ80ꢀ
14] ZhaoꢀW,ꢀChenꢀCꢀC,ꢀLiꢀXꢀZ,ꢀZhaoꢀJꢀC,ꢀHidakaꢀH,ꢀSerponeꢀN.ꢀJꢀPhysꢀ
[
2
ꢀ
ChemꢀB,ꢀ2002,ꢀ106:ꢀ5022ꢀ
[
15] HeꢀRꢀA,ꢀCaoꢀSꢀW,ꢀZhouꢀP,ꢀYuꢀJꢀG.ꢀChinꢀJꢀCatal,ꢀ2014,ꢀ35:ꢀ989ꢀ
16] XuꢀJ,ꢀWangꢀGꢀX,ꢀFanꢀJꢀJ,ꢀLiuꢀBꢀS,ꢀCaoꢀSꢀW,ꢀYuꢀJꢀG.ꢀJꢀPowerꢀSources,ꢀ
015,ꢀ274:ꢀ77ꢀ
17] TangꢀAꢀD,ꢀJiaꢀYꢀR,ꢀZhangꢀSꢀY,ꢀYuꢀQꢀM,ꢀZhangꢀXꢀC.ꢀCatalꢀCommun,ꢀ
014,ꢀ50:ꢀ1ꢀ
18] LeeꢀSꢀS,ꢀBaiꢀHꢀW,ꢀLiuꢀZꢀY,ꢀSunꢀDꢀD.ꢀWaterꢀRes,ꢀ2013,ꢀ47:ꢀ4059ꢀ
19] ChenꢀL,ꢀHuaꢀH,ꢀYangꢀQ,ꢀHuꢀCꢀG.ꢀApplꢀSurfꢀSci,ꢀ2015,ꢀ327:ꢀ62ꢀ
[20] YuꢀCꢀL,ꢀZhouꢀWꢀQ,ꢀYuꢀJꢀC,ꢀLiuꢀH,ꢀWeiꢀLꢀF.ꢀChinꢀJꢀCatal,ꢀ2014,ꢀ35:ꢀ
1609ꢀ
2
2
[
2
2
migrationꢀ ofꢀ photogeneratedꢀ carriersꢀ isꢀ promotedꢀ becauseꢀ ofꢀ
theꢀ differenceꢀ inꢀ bandꢀ positionsꢀ betweenꢀ thoseꢀ inꢀ theꢀ
[
2
Ag
electronsꢀonꢀtheꢀsurfaceꢀofꢀAg
TiO ꢀthatꢀhasꢀreactedꢀwithꢀmolecularꢀoxygenꢀtoꢀproduceꢀO
andꢀtheꢀholesꢀgeneratedꢀinꢀAg Oꢀdirectlyꢀoxidizeꢀtheꢀadsorbedꢀ
2
O‐TiO
2
ꢀ heterojunction.ꢀ Thereafter,ꢀ theꢀ photogeneratedꢀ
OꢀcanꢀtransferꢀintoꢀtheꢀCBꢀofꢀtheꢀ
•−,ꢀ
[
2
[
2
2
2
dyesꢀ orꢀ participateꢀ inꢀ theꢀ reactionꢀ toꢀ generateꢀ otherꢀ radicalꢀ
speciesꢀthatꢀoxidizeꢀtheꢀorganicꢀcompounds.ꢀThus,ꢀtheꢀseriesꢀofꢀ
oxidation‐reductionꢀreactionsꢀcausedꢀbyꢀtheꢀheterostructureꢀofꢀ
[21] HsuꢀMꢀH,ꢀChangꢀCꢀJ.ꢀJꢀHazardꢀMater,ꢀ2014,ꢀ278:ꢀ444ꢀ
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Interfaces,ꢀ2010,ꢀ2:ꢀ2385ꢀ
Ag
2
O‐TiO ꢀcanꢀrestrainꢀtheꢀfastꢀrecombinationꢀofꢀphotoinducedꢀ
2
[24] Bouzidꢀ H,ꢀ Faisalꢀ M,ꢀ Harrazꢀ Fꢀ A,ꢀ Al‐Sayariꢀ Sꢀ A,ꢀ Ismailꢀ Aꢀ A.ꢀ Catalꢀ
electron‐holeꢀpairsꢀeffectively.ꢀMeanwhile,ꢀtheꢀporousꢀstructureꢀ
ofꢀtheꢀsepioliteꢀclayꢀprovidesꢀnumerousꢀnucleationꢀsitesꢀforꢀtheꢀ
Today,ꢀ2015,ꢀ252:ꢀ20ꢀ
[25] GuoꢀYꢀD,ꢀZhangꢀGꢀK,ꢀLiuꢀJ,ꢀZhangꢀYꢀL.ꢀRSCꢀAdv,ꢀ2013,ꢀ3:ꢀ2963ꢀ
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Sol‐GelꢀSciꢀTechnol,ꢀ2015,ꢀ73:ꢀ314ꢀ
formationꢀofꢀAg
2
O‐TiO ꢀheterostructure.ꢀThisꢀsynergisticꢀeffectꢀ
2
leadsꢀtoꢀtheꢀenhancementꢀinꢀphotocatalyticꢀactivityꢀ[63].ꢀ
4.ꢀ ꢀ Conclusionsꢀ
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81ꢀ
NovelꢀAg
wereꢀ synthesizedꢀ byꢀ aꢀ simpleꢀ two‐stepꢀ method.ꢀ Theꢀ
as‐preparedꢀ Ag O‐TiO /sepioliteꢀ compositesꢀ exhibitedꢀ en‐
hancedꢀvisible‐lightꢀphotocatalyticꢀactivityꢀforꢀtheꢀdegradationꢀ
ofꢀ ARG.ꢀ Thisꢀ enhancementꢀ mayꢀ beꢀ ascribedꢀ toꢀ theꢀ porousꢀ
structureꢀ ofꢀ sepioliteꢀ andꢀ theꢀ highꢀ quantumꢀ efficiencyꢀ ofꢀ
2
O‐TiO /sepioliteꢀcompositesꢀwithꢀheterostructureꢀ
2
[
30] Renꢀ Hꢀ T,ꢀ Jiaꢀ Sꢀ Y,ꢀ Zouꢀ Jꢀ J,ꢀ Wuꢀ Sꢀ H,ꢀ Hanꢀ X.ꢀ Applꢀ Catalꢀ B,ꢀ 2015,ꢀ
176–177:ꢀ53ꢀ
2
2
[
31] KerkezꢀO,ꢀBozꢀI.ꢀChemꢀEngꢀCommun,ꢀ2015,ꢀ202:ꢀ534ꢀ
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L.ꢀApplꢀClayꢀSci,ꢀ2007,ꢀ36:ꢀ245ꢀ
[
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Ag
nanoparticlesꢀasꢀaꢀvisible‐lightꢀactiveꢀcomponentꢀenhancedꢀtheꢀ
Ag O‐TiO ꢀheterostructureꢀphotocatalyticꢀactivityꢀviaꢀsynerget‐
icꢀeffectsꢀonꢀtheꢀelectron‐holeꢀseparationꢀandꢀefficientꢀelectronꢀ
transmissionꢀ atꢀ theꢀ Ag O‐TiO ꢀ interface.ꢀ Sepioliteꢀ clayꢀ asꢀ theꢀ
2
O‐TiO
2
ꢀheterostructure.ꢀUnderꢀvisible‐lightꢀirradiation,ꢀAg
2
Oꢀ
2
2
283ꢀ
[36] AkgunꢀBꢀA,ꢀDurucanꢀC,ꢀMellottꢀNꢀP.ꢀJꢀSol‐GelꢀSciꢀTechnol,ꢀ2011,ꢀ58:ꢀ
2
2
277ꢀ

ꢀ
YuꢀDuꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ36ꢀ(2015)ꢀ2219–2228ꢀ
GraphicalꢀAbstractꢀ
2227ꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2015,ꢀ36:ꢀ2219–2228ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(15)61015‐4
FacileꢀsynthesisꢀofꢀAg O‐TiO /sepioliteꢀcompositesꢀwithꢀenhancedꢀ
visible‐lightꢀphotocatalyticꢀpropertiesꢀ
2
2
Organic dye
Products
O2
e- e- e- e-
¯
·
O
2
CB
ꢀ
YuꢀDu,ꢀDandanꢀTang,ꢀGaokeꢀZhang*,ꢀXiaoyongꢀWuꢀ
Ag O
WuhanꢀUniversityꢀofꢀTechnologyꢀ
E
g
= 1.0 eV
2
e- e- e- e-
CB
Visible light
Visible light
h+ h+ h+ h+
ꢀ
ꢀ
ꢀ
ꢀ
VB
Organic dye
Products
E
g
= 2.9 eV TiO
2
Underꢀvisible‐lightꢀirradiation,ꢀtheꢀphoto‐generatedꢀelectronsꢀonꢀtheꢀsurfaceꢀ
ofꢀAg
actedꢀwithꢀO
theꢀphoto‐generatedꢀholesꢀandꢀ O
2
Oꢀwouldꢀtransferꢀintoꢀtheꢀconductionꢀbandꢀ(CB)ꢀofꢀTiO
2
ꢀandꢀthenꢀre‐
h+ h+ h+ h+
•
−
2
ꢀmoleculesꢀtoꢀgenerateꢀ O
2
.ꢀTheꢀorganicꢀdyeꢀwasꢀdegradedꢀbyꢀ
VB
•
−ꢀactiveꢀspecies.ꢀ
2
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