hydroxide double Synthesis, characterization photocatalytic and activity of crystallineMn(II)Cr(III)-layered Catalysis Today

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Catalysis Today

jo u rn al h om ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / c a t t o d

Synthesis, characterization and photocatalytic activity of crystalline Mn(II)Cr(III)-layered double hydroxide

Zita Timár

^a,b

, Gábor Varga

^a,b

, Szabolcs Muráth

^a,b

, Zoltán Kónya

^c,d

, Ákos Kukovecz

^c,e

, Viktor Havasi

^e

, Albert Oszkó

^f

, István Pálinkó

^a,b

, Pál Sipos

^b,g,∗

aDepartmentofOrganicChemistry,UniversityofSzeged,Dómtér8,Szeged,H-6720,Hungary

bMaterialsandSolutionStructureResearchGroup,InstituteofChemistry,UniversityofSzeged,AradiVértanúktere1,Szeged,H-6720,Hungary

cDepartmentofAppliedandEnvironmentalChemistry,UniversityofSzeged,RerrichBélatér1,Szeged,H-6720,Hungary

dMTA-SZTEReactionKineticsandSurfaceChemistryResearchGroup,RerrichBélatér1,Szeged,H-6720,Hungary

eMTA-SZTE“Lendület”PorousNanocompositesResearchGroup,RerrichBélatér1,Szeged,H-6720,Hungary

fDepartmentofPhysicalChemistryandMaterialScience,UniversityofSzeged,AradiVértanúktere1,Szeged,H-6720,Hungary

gDepartmentofInorganicandAnalyticalChemistry,UniversityofSzeged,Dómtér7,Szeged,H-6720,Hungary

a r t i c l e i n f o

Articlehistory:

Received6July2016 Receivedinrevisedform 30November2016 Accepted16December2016 Availableonline23December2016

Keywords:

Layereddoublehydroxide Heterogeneousphotocatalysis Photodegradationofmethyleneblue UV–vislightirradiation

a b s t r a c t

Photocatalyticdecompositionofmethylenebluewasattemptedoveras-preparedMn(II)Cr(III)-layered doublehydroxide(LDH)containingMn(II)andCr(III)in2:1molarratio.TheLDHwaspreparedbythe co-precipitationmethod,andwasfoundtoformatpH=10andat80^◦Cfollowing24hhydrothermaltreat- ment.TheMn2Cr-LDHthusobtainedwasstructurallycharacterizedbyX-raydiffractometry,scanning electronmicroscopyandenergy-dispersiveX-rayspectroscopy.TheMn2Cr-LDHdisplayedsigniﬁcant photocatalyticactivityinthedegradationofmethyleneblueunderilluminationwithUV–vislight.The photocatalyticperformanceofthephase-pureanduncalcinedMn2Cr-LDHispracticallyidenticaltothat ofthecommerciallyavailableDegussaP25TiO2,anditwasfoundtoremainunalteredoverﬁvecon- secutivephotocatalyticruns.ThepresenceoftheLDHstructureinthecompositeistheprerequisiteof thephotocatalyticactivity.Applyingincreasingcalcinationtemperature,theLDHstructuregradually collapses,andtheMn2Cr-LDHtransformstophotocatalyticallyinactivedoubleoxide.

1. Introduction

Theuseofheterogeneousphotocatalysisinvariousindustrial processessteadilyincreases,andphotocatalystsareintheprocess ofbecomingmoreandmorepopularinavarietyofpracticalappli- cations.Eventhough traditional(non-photoactive) catalystsare stillpredominateandareproducedinmuchhigheramounts,pho- tocatalystsofferaviableandenvironmentallyfriendlyalternative in,e.g.,cleaningindustrialsewage[1,2].

Certaintypesofcompositematerialsarecapableofcatalysing transformationsofbothorganicandinorganiccompoundsinapho- tocatalyticway[3].Layereddoublehydroxides(LDHs)wereamong those tested. Atthe earlystage ofthese studies,it was shown thatboth thetreatmentofthecompositecompound beforethe reactionandthereactionconditionsplaycrucialroleinthepho-

∗ Correspondingauthorat:DepartmentofInorganicandAnalyticalChemistry, UniversityofSzeged,Dómtér7,Szeged,H−6720Hungary.

E-mailaddress:sipos@chem.u-szeged.hu(P.Sipos).

tocatalyticefﬁciency[4,5].Transitionmetal-containingLDHsare usuallypoorlycrystallinematerials[6,7],andaslongasthisisthe case,photocatalystsofpoorperformancewaspossibletobepre- paredofthem. Ontheotherhand,withincreasingcrystallinity, thespeciﬁcsurfaceareaofthephotocatalystinevitablydecreases, whichmayalsoexertanadverseeffectonthephotoactivity[8,9].

In thiswork,ouraimswere(i) thesynthesis ofmanganese- chromiumcontainingLDHsampleswithoptimalcrystallinityand (ii)theiruseasphotocatalystsinthedegradationofmethyleneblue, asmodelcompound.

ThetrivalentcationofchoicewasCr(III),becauseofitsexpected photoactivity [10]. It has been already shown that ZnCr-LDHs, duetothepresenceofCr(III),displaysphotocatalyticactivity[10], whichcanbeenhancedbydopingitwithTb(III)[11] orinclud- inggrapheneinthecomposite[12].Althoughthedivalentcationic partnerismostoftenZn(II)inthelayers,someexamplesforapply- ingCu(II),Ni(II)andevenMg(II)areknown[10,13,14].Itistobe noted, however, that Cr(III)-containing LDHswere only seldom made[15,16]anddetailsaboutthesynthesisisevenmorescarcely

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efﬁciency. Accordingly, the following experimental parameters weresystematically varied duringthe preparation:pH (from 8 to11);thepreparationtemperature(from25to80^◦C),theratio betweenthe di-andthetrivalent ions (from 2:1 to4:1).¹ Both nitrateandchloridesaltswereusedforthesyntheses;however, chloridesaltswereomitted,asitwasobservedthattheLDHdidnot precipitatefromthereactionmixtureifchloridesaltswereutilized.

Duringatypical,e.g.,Mn₂Cr-LDH,synthesis viaco-precipitation, a mixture of analytical grade Mn(NO3)2×4H2O (30mmol) and Cr(NO₃)₃×9H₂O(15mmol) (bothareReanal products)wasdis- solvedin100mLofdistilledwater,andwasstirredatpH=10for 24h.ThepHwasadjustedviaaddingasolutionof3MNaOHtothe system,thepHofwhichwasmonitoredwithacalibratedglasselec- trode.Thesuspensionwasﬁltered,washedwithdistilledwaterand theblackish-bluecrystalsweredriedfor24hinvacuooverP2O5. Hydrothermaltreatment[22]wascarried outin aclosed Pyrex glassvesselat80±3^◦C,usingcontinuousstirring.Theresulting suspensionwasﬁlteredanddriedfor24hinvacuooverP2O5.

Thematerialspreparedwerecharacterizedbyvariousmethods.

X-raydiffractometry(XRD)wasusedtoverifythesuccess(or thefailure)ofthepreparationoftheLDHs,sinceLDHsareknown tohavecharacteristicXRDpatterns.TheXRDtracesofthevarious sampleswererecordedonaRigakuXRD-6000diffractometer,using CuK␣radiation(␭=0.15418nm)at40kV,30mA.

Scanning electron microscopy (SEM) was also employed to makethecharacteristichexagonalmorphologyoftheLDHsvisi- ble.ThemorphologyofthinﬁlmswasinvestigatedusingaHitachi S-4700scanningelectronmicroscopewiththeacceleratingvoltage of10–18kV.

Energy dispersive X-ray (EDX) microspectroscopy gives a (semi)quantitative picture of the components in the material synthesized. EDX data wereobtained on a Röntec QX2 energy dispersivemicroanalyticalsystemfromtwodifferentpartsofthe sample.ThesystemwascoupledtotheSEM,andprovidedwiththe elementalmapofthechosenregionofthesample.

To identify interlayer anions, IR spectra of some selected sampleswererecorded.Forthis,aBIO-RADDigilabDivisionFTS- 65A/896FT-IRspectrophotometerwith4cm⁻¹ resolution,using DRS technique was employed. Spectra in the 4000–600cm⁻¹ wavenumber range were recorded, but the most relevant 1850–600cm⁻¹rangewillbedisplayedanddiscussed.256scans werecollectedforeachspectrum.

Thebandgapofthematerialpreparedwasdeterminedfromthe UV–visspectrumregisteredonOceanOpticsUSB4000spectrome-

1 IntheacronymusedfortheLDHsprepared,i.e.,MnnCr,nstandsfortheMn:Cr molarratiointhesolid.

Fig.1.XRDpatternsforthesolidsubstancesobtainedfromasolutioncontaining Mn(II)andCr(III)inamolarratioof2:1atvariouspH-s:A:pH=9,B:pH=10,C:

pH=11;thetemperatureofthereactionmixturewasT=25^◦C.

terwithaDH-2000-BALUV–vis-NIRlightsourcemeasuringdiffuse reﬂectancemodeandusingBaSO₄asreference.Thespectrumwas analyzedwiththeSpectraSuitepackage.Theband-gapenergywas determinedfromtheextrapolationofthestraightsectionofthe modiﬁedKubelka-Munkfunctionplottedvs.energyoftheincident light.Bandgapdeterminationwasdoneonlyforthephase pure LDH,asthisspecimenwasexclusivelyusedforthephotocatalytic tests.

Forthephotocatalytictests,1mgofcatalyst in200mLsolu- tionwasused,thepHwascontrolledbyabufferbasedonKH2PO4

(0.15M).Todeterminethebestparametersetforthephotocat- alyticdegradation,thepHofthesolution(7–10),thetemperatureof thereactionmixture(8–50^◦C)andtheconcentrationofsubstrate, methylenebluethatis(productofAldrichChemicals)weresystem- aticallyvaried.ThephotoreactorwasanopenPyrexglassvessel.An OSRAMPowerStarHCl-TC70W/WDLlamp(␭=360–800nm)was appliedataﬁxedposition)forirradiatingthereactor;theirradi- ationtookplacefromverticalposition,ca.10cmfromtheinletof thevessel.ThedegradationofthedyewasfollowedbyUV–visspec- trometryonaShimadzuUV–1650spectrophotometer.Absorbance valuesatabsorptionmaximumofmethyleneblue(665nm)were recorded.

The X-ray photoelectron spectra (XPS) of the freshly pre- paredandtheusedsamplesweretakenwithaSPECSinstrument equipped with a PHOIBOS 150 MCD 9 hemispherical electron energyanalyzer(Germany)operatedintheFATmode.Theexci- tationsourcewastheK␣radiationofmagnesium(h␯=1253.6eV) andaluminum(h␯=1486.3eV)anodes.TheX-raygunwasoper- atedat180Wpower(12kV,15mA).Thepassenergywassetto 20eV,thestepsizewas25 meV,andthecollectiontimeinone channelwas150ms.

3. Resultsanddiscussion

3.1. PreparationandstructuralcharacteristicsoftheMn₂Cr-LDH samples

During thepreparative work, ﬁrst, the synthesis of Mn_nCr- LDH with appreciable crystallinity was aimed at. As simple co-precipitationwithouthydrothermalpost-treatmentisreported tobea veryefﬁcientwayofLDH preparationingeneral,therefore,thistrivialsynthesisroutewasinitiallyemployed[22,23].As itisshowninFigs.1–3,viausingthispreparationmethod,the

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Fig.2.XRDpatternsforthesolidsubstancesobtainedfromasolutioncontaining Mn(II)andCr(III)atvariousmolarratios:A:2:1;B:3:1;C:4:1.Thesyntheseswere performedatpH=10andT=25^◦Cthroughout.

Fig.3.XRDpatternsforthesolidobtainedfromasolutioncontainingMn(II)and Cr(III)inamolarratioof2:1atvarioustemperatures:A:T=40^◦C,B:T=60^◦C,C:

T=80^◦C.ThepHofthereactionmixturewas10throughout.Theweakfeatureat2

≈12^◦denotedby(003)islikelytobeareﬂectionstemmingfromsomeMn2Cr-LDH.

desiredLDHformationcouldnotbeobservedeitherviasystem- aticallychangingthepH(Fig.1),thereactantratio(Fig.2)orthe temperature(Fig.3).Thelackofthecharacteristic(003)reﬂectionof theLDHsaround2≈12^◦(exceptfortheweakfeaturecorrespond- ingtoinFig.3C,seebelow)unambiguouslyprove,thattheuseof these(otherwisecommonlyemployed)synthesisparametersdid notleadtopureandhighlycrystallineMnnCr-LDH.

InFig.3C,undersuperambientconditions(T=80^◦C),thefor- mationofsomeMn₂Cr-LDHcouldbeobserved.Accordingly,itwas hypothesised,thatalongerhydrothermaltreatmentmayleadto theformationofthedesiredMn₂Cr-LDH.Uponusinghydrother- maltreatmentat80^◦Cfor24h,theappearanceoftheXRDpatterns characteristictotheLDH(Fig.4)couldbeobserved.Fromthis,itcan alsobestatedthattheby-productsalsodisappeared,andthebasal spacingwascalculatedasd=0.744nm(withestimateda[14,24]

andcalculatedclatticeparametersof4.7nmand2.23nm,respec- tively[24]).OnthebasisoftheXRDpatterns,thesampleobtained couldbeconsideredasphasepure.TheXRDpatternandtheBET surfacearea(56.4m²/g)ofthesuccessfullypreparedsampledid

Fig.4. XRDpatternsforthesolidsubstancesobtainedfromasolutioncontaining Mn(II)andCr(III)inamolarratioof2:1,subjectedtohydrothermaltreatmentfor 24hatvarioustemperatures:A:T=40^◦C,B:T=60^◦C,C:T=80^◦C.ThepHofthe reactionmixturewas10throughout.

notchangewithintwomonthsfromthesynthesisindicatingcon- siderablystability.TheaveragethicknessoftheLDHparticleswere calculatedfromtheDebye-Scherrerequationandwasfoundtobe 3.1nm.

Forthephase-pureMn₂Cr-LDHspecimen,theXRDpatternof whichisshowninFig.4C,theSEMimageswerealsorecorded.From thepictures,thelaminarhexagonally-shapedmorphology,typical ofLDHscanbeobserved(Fig.5).

The SEM–EDX elemental map obtained for the phase-pure Mn2Cr-LDHsampleisdisplayedinFig.6.Itshowsthatboththe manganeseandchromiumareevenlydistributed.

TheIRspectrumofthephase-pureMn₂Cr-LDH(Fig.7)showsthe characteristicvibrationoftheintercalatedNO3−ionat1405cm⁻¹ [25].AstheIRbandofthecarbonateionappearsveryclosetothatof nitrate,somecontributionfrompossiblecarbonatecontamination mayalsobepresentinthissignal.Theothertwodistinctvibration bandscorrespondtotheLDH structure,andareassociatedwith

␤-OH(1630cm⁻¹)[26]andCr−O(780cm⁻¹)modes[25].

DRSspectrumoftheas-preparedphasepureMn₂Cr-LDHwas alsorecorded (Fig.8).Assuming direct bandgaptransitionand extrapolatingthestraightsectionofthemodiﬁedKubelka-Munk functionplottedvs.energyoftheincidentlightresultedinbandgap energyof1.46eV.Thiscorrespondsto850nmwavelength,which isconsistentwiththeblackish-bluecolourofthespecimen.Tak- ingindirectbandgaptransition,itsenergywasnotpossibletobe accuratelycomputed(beingatca.0.8eVandthereforefallingout- sidethemeasurementrangeoftheinstrument).Comparingthetwo typesofbandgapenergies,directbandgaptransitionseemstobe morerealisticforthephasepureMn₂Cr-LDHsemiconductor.

3.2. PhotocatalysisofmethyleneblueoverMn₂Cr-LDH

Thephotocatalyticactivityofthephase-pureMn2Cr-LDHcom- positewastestedinthephotodegradationofmethyleneblue(MB) underUV–vislightirradiation.Intheabsenceofthecatalyst,itwas observedthatthedecompositionofMBwasnegligibleevenafter anextendedperiodoftime.Itwasreportedpreviouslybyothers thatuponUV–visirradiation,morethan10%oftheMBdecomposed within6h;however,thosereactionswereperformedunderacidic conditions[27].Atthebeginningofthecatalyticexperiments,MB wasallowedtoadsorbover thesurfaceofthecatalysts;ineach case,onehour“darktime”wasallowed,beforeswitchingtheillu-

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Fig.6. SEM–EDXelementalmapsforthephase-pureMn2Cr-LDH(hydrothermallytreatedatT=80^◦Cfor24hatpH=10).

minationon.TheinitialdecreaseoftheMBconcentrationpriorto switchingonthelightsourceismostprobablyassociatedwiththis surfaceabsorptionofthesubstrate.

3.2.1. TheeffectofpHduringthereaction

The most important parameter that affect degradation was foundtobethepHofthesolution(Fig.9).Itwasfoundthatthe photoreactioncommencedwithaninductionperiodateachpH, andwasthefaster,whenthepHofthesolutionwasadjustedto9.

Undertheseconditions,thedegradationoftheMBreached>80%

after120min.AthigherandatlowerpH,thereactionratewas signiﬁcantlylower.AtpH=7,apparentlythec/c₀ vs.timecurve startsincreasingafterca.60min(Fig.9A),mostprobably,dueto theformationofsomeintermediate,whichalsoabsorbsthelightat thedetectionwavelength.Theseobservationsstronglysuggestthat themechanismofthephotodegradationofMBoverMn2Cr-LDH compositeisstronglypH-dependent[28].

3.2.2. EffectofMBconcentration

TheinitialconcentrationoftheMBcanbeanimportantfactor in the photodegradation reaction. Therefore, in further experiments,itsconcentrationwassystematicallychangedfrom20mg/L to40mg/L.Fig.10atteststhatthedegreeofdegradationvaried inthe70–92%range.Takingintoconsiderationtheerrorsinthese photocatalytictestmeasurements,itseemsreasonabletosuggest, thatintheMBconcentrationrangecovered,thereactionrateis roughlyindependentofthesubstrateconcentration.Inthesub- sequentmeasurements,c₀=30mg/Lsubstrateconcentrationwas employed.

3.2.3. Effectofphotocatalystcalcination

During thesubsequent experiments,thephase-pure Mn₂Cr- LDHcompositewassubjectedtoannealingatvarioustemperatures (250,500and750^◦C)for24h.Followingthiscalcinationprocedure, thephotodegradationexperimentswererepeatedusingtheopti- mized decomposition conditions (c₀=30mg/L,pH=9, T=25^◦C).

Theeffectofthevariouscalcinationtemperaturesonthephoto-

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Fig.7.IRspectrumofphase-pureMn2Cr–LDH.

Fig.8. TaucplotofthephasepureMn2Cr-LDH.

Fig.9. ThephotodegrationofMBexpressedasc/c0asafunctionofillumination timeoverphase-pureMn2Cr-LDHcompositeatvariouspHvaluesandat25^◦C.A:

pH=7,B:pH=9,C:pH=10(initialconcentrationofMB:c0=30mg/L).

Fig.10.ThephotodegrationofMBexpressedasc/c0asafunctionofillumination timeoverphase-pureMn2Cr-LDHcompositeatvariousinitialconcentrationofMB.

A:20mg/L;B:30mg/L;C:40mg/LpH=9,T=25^◦C.

Fig.11.ThephotodegrationofMBexpressedasc/c0asafunctionofillumination timeoverphase-pureMn2Cr-LDHcompositecalcinedatvarioustemperaturesfor 24h.Calcinationtemperatures:A:nocalcination;B:250^◦C;C:500^◦C;D:750^◦C.

Conditionsofphotodegradation:c0=30mg/L;pH=9,T=25^◦C.

catalyticactivityaredisplayedinFig.11,whiletheXRDpatternsof thecalcinedphase-pureMn₂Cr-LDHcompositeisshowninFig.12.

ItwasobservedthatamongtheMn₂Cr-LDHsamples,theuncal- cinedphotocatalystexhibitedthehighestphotocatalyticactivity.

Increasingthecalcinationtemperatureresultedin adrasticand systematicdecreaseinthephotocatalyticactivity.Calcinationat 750^◦Cfor24hresultedinamaterial,whichhadpracticallynopho- tocatalyticactivitywhatsoever.FromFig.12,itis apparentthat theincreasingcalcinationtemperatureresultedinagradualcol- lapseoftheLDHstructure, and(most probably)resultedin the progressiveformationofsomesortofdoubleoxide.Lattercom- positehasnophotocatalyticactivity,asopposedtothecomposite havingthelayeredstructure.Thephotocatalyticactivityofthevar- iousMn2Cr-LDHsamplesclearlycorrelatewiththeproportionof thelayeredstructureremainingaftercalcination.Thisobservation stronglysuggeststhatthepresenceoftheorderedlayeredstructure isadvantageousforthephotocatalyticactivityofthesecomposites inMBdegradation;thehighlyregularstructurehelpsinpreserving theoxidationstateofthecationiccomponentsoftheas-prepared LDH.

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Fig.12. XRDpatternsofphase-pureMn2Cr-LDHsamplescalcinedatvarioustem- peraturesfor24h.Calcinationtemperatures:A:uncalcinedsample,B:250^◦C,C:

500^◦C,D:750^◦C.

Tocomparetheperformance ofourbestMn₂Cr-LDHsample withthat of the commerciallyavailable Degussa P25 TiO₂, MB photodegradationexperiments were performed (Fig. 13) under identicalconditionsemploying1mgphotocatalystofbothsolidsin 200cm³testsolution.Fromthisgraph,itisapparentthatthepho- tocatalyticperformanceoftheMn2Cr-LDHcompositewasalmost thesameasthatofP25.

Thestability of theMn₂Cr-LDHphotocatalyst wastested by reusingthesamplesfivetimesintheMBdegradationexperiment, employing the optimaldegradation conditions. Aftereach run, thephotocatalystwasremovedviafiltrationanddriedoverP₂O₅ invacuo,intheusualway.AsshowninFig.14,thedegradationeffi- ciencydidnotchangesignificantlyafterfivecycles,suggestingthat thephotocatalystpreparedbyusisreasonablystableandresistant tophotocorrosion.

3.2.4. TheXPSanalysisoftheas-preparedandtheusedcatalyst TheoxidationofthecationiccomponentsoftheLDHwasstudied withX-rayphotoelectronspectroscopybeforeandafterthereac- tion(Fig.15).Thephotoelectronspectrarevealedthattheoxidation stateofneithercationiccomponentchangedduringthecatalytic reaction.

Fig.13.ThephotodegrationofMBexpressedasc/c0asafunctionofillumination time.A:Nophotocatalystadded;B:overDegussaP25TiO2;C:overphase-pure, uncalcinedMn2Cr-LDHcomposite.Conditionsofphotodegradation:c0=30mg/L;

pH=9,T=25^◦C.

Fig.14.ThephotodegrationofMBexpressedasc/c0asafunctionofillumina- tiontimeoverﬁveconsecutiveruns,denotedbyA,B,C,DandE.Conditionsof photodegradation:c0=30mg/L;pH=9,T=25^◦C.

4. Conclusions

Insearchforalayereddoublehydroxidethathasappreciable heterogeneousphotocatalyticactivity,ﬁrstthesynthesisofcrys-

Fig.15.TheX-rayphotoelectronspectraoftheMn2Cr-LDHcatalystas-prepared(A)andused(B).

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tallineMn₂Cr-LDHwasattempted.Phase-pureLDHwasisolated fromsolutions containing theMn(II) and Cr(III) in a 2:1molar ratioandatpH=10.Fortheformationofphase-pureMn₂Cr-LDH, hydrothermaltreatmentat80^◦Cfor24hwasfoundtobeneces- sary;thiswayaMn2Cr-LDHsamplewithreasonablecrystallinity wasobtained.Thismaterialprovedtobeanefﬁcientphotocatalyst inthedegradationreactionofMB.Itwasfoundthatoptimalpho- tocatalyticperformancewasobtained,whenthepHofthesolution wasadjustedto9,andwhenthephotocatalystwasnotsubjectedto anycalcinationbeforethedegradationexperiment.Thephase-pure anduncalcinedMn2Cr-LDHphotocatalystdisplayedphotocatalytic performancethatwasfoundtobepracticallyidenticaltothatofthe commerciallyDegussaP25TiO₂.

Acknowledgment

This work was supported by the National Science Fund of HungarythroughOTKANKFI106234andGINOP-2.3.2-15-2016- 00013grants.Theﬁnancialhelpishighlyappreciated.

References

[1]S.Sikarwar,R.Jain,WaterAirSoilPollut.226(2015)277.

[2]G.Karaca,Y.Tasdemir,J.EnvironSci.HealthATox.HazardSubst.EnvironEng.

48(2013)855–861.

[3]E.Dvininova,M.Ignat,P.Barvinschi,M.A.Smithers,E.Popovici,J.Hazard.

Mater.177(2010)150–158.

[4]N.Ahmed,Y.Shibata,T.Taniguchi,Y.Izumi,J.Catal.279(2011)123–135.

[5]Y.Zhao,M.Wei,J.Lu,Z.LinWang,X.Duan,ACSNano3(2009)4009–4016.

[6]M.delArco,M.V.G.Galiano,V.Rives,R.Trujillano,P.Malet,Inorg.Chem.35 (1996)6362–6372.

[7]H.Wan,J.Liu,Y.Ruan,L.Lv,L.Peng,X.Ji,L.Miao,J.Jiang,ACSAppl.Mater.

Interfaces7(2015)15840–15847.

[8]M.F.deAlmeida,C.R.Bellato,A.H.Mounteer,S.O.Ferreirac,J.L.Milagres,L.D.L.

Miranda,Appl.Surf.Sci.357(2015)1765–1775.

[9]K.Abderrazek,F.S.Najoua,E.Srasra,Appl.Clay.Sci.119(2016)229–235.

[10]N.Baliarsingh,K.M.Parida,G.C.Pradhan,Ind.Eng.Chem.Res.53(2014) 3834–3841.

[11]Y.Fu,F.Ning,S.Xu,H.An,M.Shao,M.Wei,J.MaterChem.A4(2016) 3907–3913.

[12]J.L.Gunjakar,I.Y.Kim,J.M.Lee,N.-S.Lee,S.-J.Hwang,EnergyEnviron.Sci.6 (2013)1008–1017.

[13]A.deRoy,C.Forano,J.P.Besse,LayeredDoubleHydroxides:Presentand Future,in:V.Rives(Ed.),NovaSciencePublishers,Inc,NewYork,2006,pp.

1–39(Ch.1).

[14]J.W.Boclair,P.S.Braterman,J.Jiang,S.Lou,F.Yarberry,Chem.Mater.11 (1999)303–307.

[15]V.R.Choudhary,D.K.Dumbre,B.S.Uphade,V.S.Narkhede,J.Mol.Catal.A215 (2004)129–135.

[16]J.W.Boclair,P.S.Braterman,Chem.Mater.11(1999)298–302.

[17]E.Horváth,P.R.Ribiˇc,F.Hashemi,L.Forró,A.Magrez,J.Mater.Chem.22 (2012)8778–8784.

[18]L.Xiong,Y.Yang,J.Mai,W.Sun,C.Zhang,D.Wei,Q.Chen,J.Ni,Chem.Eng.J.

156(2010)313–320.

[19]E.Horváth,I.Szilágyi,L.Forró,A.Magrez,J.Coll.InterfaceSci.416(2014) 190–197.

[20]S.Xia,L.Zhang,G.Pan,P.Qian,Z.Ni,Phys.Chem.Chem.Phys.17(2015) 5345–5351.

[21]E.M.Seftel,M.Niarchos,Ch.Mitropoulos,M.Mertens,E.F.Vansant,P.Cool, Catal.Today252(2015)120–127.

[22]J.H.Choy,Y.M.Kwon,K.S.Han,S.W.Song,S.H.Chang,Mater.Lett.34(1998) 356–363.

[23]F.M.Labajos,V.Rives,M.A.Ulibarri,Mater.Sci.27(1992)1546–1552.

[24]T.P.F.Teixeira,S.F.Aquino,S.I.Pereira,A.Dias,Braz.J.Chem.Eng.31(2014) 19–26.

[25]F.A.Miller,C.H.Wilkins,Anal.Chem.24(1952)1253–1294.

[26]M.Mora,M.I.López,C.Jiménez-Sanchidrián,J.R.Ruiz,SolidStateSci.13 (2011)101–105.

[27]Y.Zhou,L.Shuai,X.Jiang,F.Jiao,J.Yu,Adv.PowderTechnol.26(2015) 439–447.

[28]K.Abderrazek,F.S.Najoua,E.Srasra,Appl.Clay.Sci.119(2016)229–235.