ChineseJournalofCatalysis34(2013)2004–2008 

a v a i l a b l e   a t  www . s c i e n c e d i r e c t . c om  

j o u r n a l   h omep a g e :  www . e l s e v i e r . c om / l o c a t e / c h n j c

Communication (Dedicated to Professor Yi Chen on the occasion of his 80th birthday) 

Fluoride‐freesynthesisofanataseTiO2crystalsrichin(001)facetsinthepresenceofcationicpolymer

WeiweiChang,YanLiu,QiSun,XiangjuMeng*,Feng‐ShouXiao#DepartmentofChemistry,ZhejiangUniversity,Hangzhou310028,Zhejiang,China

A R T I C L E I N F O  

A B S T R A C T

Articlehistory:Received14June2013Accepted16August2013Published20November2013

ControllablesynthesesofanataseTiO2richin(001)facetshaveattractedmuchattentionbecauseoftheexcellentphotocatalyticactivityof thismaterial indyedegradation.Thesesynthesesarenor‐mally performed in the presence of fluoride,which is environmentally unfriendly. In this study,anataseTiO2crystalsrichin(001)facetsweresuccessfullysynthesizedinthepresenceofacationicpolymer and characterized using X‐ray diffraction, scanning electron and transmission electronmicroscopies,andultraviolet‐visiblespectroscopy.PhotocatalytictestsshowedthatthismaterialisveryactiveinthedegradationofmethylorangecomparedwithconventionalanataseTiO2crystalsandacommercialP25photocatalyst.Thehighactivityisattributedtotherich(001)facetstransla‐tion.

©2013,DalianInstituteofChemicalPhysics,ChineseAcademyofSciences.PublishedbyElsevierB.V.Allrightsreserved.

Keywords:Anatasetitanium(001)facetsSolvothermalsynthesisCationicpolymerHighphotocatalyticactivity

 

AnataseTiO2crystalshavebeenextensivelystudiedbecauseof theirwiderangeofapplications inphotocatalysis [1], solarenergy conversion [2], photonic devices [3], and sensors [4].Generally,the(001)facetsofanataseTiO2crystalsareconsid‐eredtobeveryactiveinphotocatalysis[5].However,itisverydifficulttosynthesizeanataseTiO2crystalsrichin(001)facetsbecauseofthehighsurfaceenergy.ThemostexposedsurfaceofanataseTiO2crystalsisthethermodynamicallystable(101)facet,whichcanaccountformorethan94%ofthetotalcrystalsurface in conventional anatase TiO2 crystals [6]. There istherefore great interest in the development of controllablesynthesesofanataseTiO2crystalsrichin(001)facets.

Sinceabreakthrough in synthesizinganataseTiO2 crystalswithalargepercentageof(001)facetsinthepresenceoffluo‐ride species was made [7], much effort has been devoted todevelopingnewroutesforpreparinganataseTiO2crystalsrich

in (001) facets in thepresenceof fluoride species [8–13].Forexample, Alivov et al. [8] reported transformation of TiO2nanotubes to pyramid‐shaped TiO2 nanoparticleswith a highpercentageof (001) facets in thepresenceof fluoridespecies,and Han et al. [13] successfully synthesized TiO2 nanosheetswithahighpercentageofexposed(001)facetsinthepresenceofahighlyconcentratedHFsolution.Despitemuchencourag‐ing progress in recent years, the synthesis of anatase TiO2crystalsrichin(001)facetsstillrequiresthepresenceof fluo‐ridespecies;thesearehighlytoxicandcorrosiveinthegasorliquid state. It is therefore highly desirable to develop a newsynthetic strategy for the fluoride‐free synthesis of anataseTiO2crystalsrichin(001)facets.

Inthispaper,wereportanewfluoride‐freesynthesisofan‐ataseTiO2crystalsrichin(001)facetsinthepresenceofacat‐ionic polymer (poly(diallyldimethylammonium chloride),

*Correspondingauthor.Tel:+86‐571‐88273698;E‐mail:mengxj@zju.edu.cn #Correspondingauthor.Tel:+86‐571‐88273282;E‐mail:fsxiao@zju.edu.cnThisworkwassupportedbytheNationalNaturalScienceFoundationofChina(U1162201and21003107),theNationalHighTechnologyResearchandDevelopmentProgramofChina(2013AA065301),theScienceandTechnologyInnovativeTeamofZhejiangProvince(2012R10014‐01),andtheFundamentalResearchFundsfortheCentralUniversities(2013XZZX001). DOI:10.1016/S1872‐2067(12)60679‐2|http://www.sciencedirect.com/science/journal/18722067|Chin.J.Catal.,Vol.34,No.11,November2013

WeiweiChangetal./ChineseJournalofCatalysis34(2013)2004–2008

PDDA‐Cl).Interestingly,theobtainedmaterialisveryactiveinthe photocatalytic degradation of methyl orange (MO) com‐pared with conventional anatase TiO2 crystals and the com‐mercialP25photocatalyst.

InatypicalsynthesisofanataseTiO2crystalsrichin(001)facets,4mmolof titaniumtetrabutoxide(Aladin)wereaddeddropwise to 30mL of ethanol. After stirring for 4 h, 1.5 g ofPDDA‐Cl were added. Then the mixture was continuouslystirred overnight at room temperature and transferred to aTeflon‐lined stainless‐steel autoclave. After crystallization at160Cfor4d,theproductswereseparatedbycentrifugation,washedwithdeionizedwater,anddriedat100Cfor1h.Aftercalcinationat550C,anataseTiO2crystalsrichin(001)facetswerefinallyobtained;thiswasdesignatedTiO2‐P.

Figure1(a)showsX‐raydiffraction(XRD)patternsofsam‐ples synthesized in thepresenceorabsenceofPDDA‐Cl.BothsampleshavepeaksindexedtoanataseTiO2crystals(JCPDSNo.21‐1272). Interestingly, theultraviolet‐visible (UV‐Vis)diffusereflectance spectrumofTiO2‐P synthesized in thepresenceofPDDA‐ClshowsstrongerabsorptioninboththeUVandvisibleregionsthanthoseofTiO2crystalssynthesizedintheabsenceof PDDA‐Cl (Fig. 1(b)). This is in good agreementwith previ‐ouslyreportedresults[14–16]andisattributedtodifferencesamongthesamplemorphologies.

Figure 2 shows scanning electron microscopy (SEM) andtransmission electron microscopy (TEM) images of variousTiO2 samples. The SEM images of the TiO2‐P sample showwell‐defined rectangular crystals with side lengths of about1.2–1.5mandthicknessesofabout0.5m.AccordingtothesymmetryofanataseTiO2crystals,forasingletruncatedpyra‐midineachanataseTiO2crystal,thetopflatandsquaresurfaceshouldbe (001) facets, and the isosceles trapezoidal surfacesshouldbe(101)facets.Figure2(c)showsahigh‐magnification

TEMimageofTiO2‐Pviewedfromthetop(theinsetisthefastFouriertransform(FFT)pattern);theobservedsetsoflatticesoriented perpendicular to each other with an equal fringespacingof0.19nmareingoodagreementwiththe(200)and(020)planesofanataseTiO2[17,18].Thisimageshowsatypi‐caltopviewof(001)facetsonanataseTiO2.Basedontheabove

20 30 40 50 602/( o )

Inte

nsit

y

(1)

(2)

(101

)

(004

)

(200

)

(105

)(2

11)

(213

)

(a)

200 300 400 500 600 700 800

0.0

0.3

0.6

0.9

1.2

1.5

(1)

Wavelength (nm)

(2)

Abs

orba

nce

(b)(a)

Fig.1.XRDpatterns(a)andUV‐Visspectra(b)ofTiO2crystalssynthe‐sizedintheabsence(1)andpresence(2)ofPDDA‐Cl.

Fig.2.SEM(a,b)andTEM(c)imagesofTiO2‐Psample(insetisthecorrespondingFFTpatternof(c));SEM(d)andTEM(e,f)imagesofTiO2samplesynthesizedintheabsenceofPDDA‐Cl.

(d)

20 nm

50 nm

(e) (f)

(a) (b) (c)

WeiweiChangetal./ChineseJournalofCatalysis34(2013)2004–2008

structural information, the percentage of highly active (001)facetsintheTiO2‐Psamplewasestimatedtobeashighas72%.In contrast, the TiO2 sample synthesized in the absence ofPDDA‐Cl ismainlycomposedofsphericalcrystalsofdiameter3–5m(Fig.2(d)).TheTEMimageofthesampleshowsalat‐ticespacingofabout0.35nm,whichisconsistentwiththatofthe(101)facets(Fig.2(f)).

ThedegradationofMOwaschosenasamodeltodeterminethephotocatalyticactivityof theTiO2‐Psample;commerciallyavailableP25(averageparticlesize25nm)wasusedasaref‐erenceforcomparison.ThephotocatalyticactivityoftheTiO2‐PsampleismuchhigherthanthatofTiO2synthesizedintheab‐senceofPDDA‐Cl,andevenhigherthanthatofthecommercialP25 catalyst, as shown in Fig. 3(a). The anatase phase is thesame(Fig.1(a))andthesurfaceareasaresimilarfortheTiO2‐P(48m2/g)andconventionalTiO2(38m2/g),sothemuchhigheractivityofTiO2‐PthanthatofconventionalTiO2isattributedtothemuchlargernumberofexposed(001)facetsintheTiO2‐Pcrystals.TheTiO2 crystals rich in (001) facetsareveryactiveforMOdegradationcomparedwithconventionalTiO2.ItisalsoworthmentioningthattheTiO2‐Psamplehadverygoodrecy‐clability.Whenthesamplewasrecycledfourtimes,thesampleactivitywasstillcomparablewiththatofthefreshcatalyst(Fig.3(b)).

TheroleofPDDA‐ClinthesynthesisofTiO2crystalsrichin(001)facetscanbeexplainedbyinteractionsofsurfaceTispe‐cieswithPDDA‐Clasaresultofelectrostaticcoulombicforces,giving Ti4+‐Cl−‐PDDA+. Similar interactions have been widelyobservedintheassemblyofcationicsurfactants,chlorides,andinorganic cations in the synthesis of mesoporous materials[19–21].Because theamountof exposedTion the (001) sur‐face is twice that on the (101) surface, PDDA‐Cl species aremore likely to be adsorbed on the (001) surface, leading tosuppressionofgrowthinthe(001)crystaldirection[22].Asaresult, the TiO2‐P sample is rich in photocatalytically active(001)facets.

In summary, we successfully synthesized anatase TiO2‐Pcrystalsrichin(001) facets in thepresenceofPDDA‐ClunderF‐freeconditions.TheactivityoftheTiO2‐PinMOdegradation

ismuchhigher thanthoseofconventionalTiO2crystalsandacommercial P25 catalyst. The controllable synthesis of oxideswith preferred crystal facets usingPDDA‐Cl is potentially im‐portantforthefuturedesignandpreparationoffunctionalox‐idematerials.

References

[1] AsahiR,MorikawaT,OhwakiT,AokiK,TagaY.Science,2001,293:269

[2] ChenDH,HuangFZ,ChengYB,CarusoRA.AdvMater,2009,21:2206

[3] ChenJIL,VonFreymannG,ChoiSY,KitaevV,OzinGA.AdvMater,2006,18:1915

[4] TangH,PrasadK, SanjinésR, LévyF.SensorsActuatorsB, 1995,26:71

[5] LiuM,PiaoLY,ZhaoL,JuST,YanZJ,HeT,ZhouCL,WangWJ.ChemCommun,2010,46:1664

[6] DieboldU.SurfSciRep,2003,48:53[7] YangHG,SunCH,QiaoSZ,ZouJ,LiuG,SmithSC,ChengHM,Lu

GQ.Nature,2008,453:638[8] AlivovY,FanZY.JPhysChemC,2009,113:12954[9] LiuSW,YuJG,JaroniecM.JAmChemSoc,2010,132:11914[10] XiangQJ,YuJG.ChinJCatal,2011,32:525[11] LüKL,ChengB, Yu J G, LiuG.PhysChemChemPhys, 2012, 14:

5349[12] YangHG,LiuG,QiaoSZ,SunCH,JinYG,SmithSC,ZouJ,ChengH

M,LuGQ.JAmChemSoc,2009,131:4078[13] HanXG,KuangQ,JinMS,XieZX,ZhengLS.JAmChemSoc,2009,

131:3152[14] Wang C, Deng Z X, Zhang GH, Fan S S, Li Y D.PowderTechnol,

2002,125:39[15] GuoYG,HuJS,LiangHP,WanLJ,BaiCL.AdvFunctMater,2005,

15:196[16] WangYW,ZhangLZ,DengKJ,ChenXY,ZouZJ.JPhysChemC,

2007,111:2709[17] JungMH,ChuMJ,KangMG.ChemCommun,2012,48:5016[18] FangWQ,YangXH,ZhuHJ,LiZ,ZhaoHJ,YaoXD,YangHG.J

MaterChem,2012,22:22082[19] HuoQS,MargoleseDI,CleslaU,FengPY,GlerTE,SiegerP,Leon

R,PetroffPM,SchüthF,StuckyGD.Nature,1994,368:317[20] HuoQS,MargoleseDI,CieslaU,DemuthDG,FengPY,GierTE,

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0

(4)

(3)

(2)

(1)

C/C

0

Time (min)

(a)

0 20 40 60 80 100 1200.0

0.2

0.4

0.6

0.8

1.0

cycle 5cycle 4cycle 3cycle 2

C/C

0

Time (min)

cycle 1

(b)

Fig.3.(a)PhotocatalyticpropertiesofvariousTiO2samplesinMOdegradationunderUVirradiation(MO,C0=10mg/L).(1)Blank;(2)TiO2synthe‐sizedintheabsenceofPDDA‐Cl;(3)P25;(4)TiO2‐P.(b)RecyclabilityoftheTiO2‐Psample.

WeiweiChangetal./ChineseJournalofCatalysis34(2013)2004–2008

SiegerP,FirouziA,ChmelkaBF,SchüthF,StuckyGD.ChemMater,1994,6:1176

[21] XiaoFS,WangLF,YinCY,LinKF,DiY,LiJX,XuRR,SuDS,Schl‐

glR,YokoiT,TatsumiT.AngewChemIntEd,2006,45:3090 [22] ZhaoWN,LinHX,LiY,ZhangYF,HuangX,ChenWK.JNatGas

Chem,2012,21:544

GraphicalAbstract

Chin.J.Catal.,2013,34:2004–2008 doi:10.1016/S1872‐2067(12)60679‐2

Fluoride‐freesynthesisofanataseTiO2crystalsrichin(001)facetsinthepresenceofcationicpolymer

WeiweiChang,YanLiu,QiSun,XiangjuMeng*,Feng‐ShouXiao*ZhejiangUniversity

AnataseTiO2 crystals rich in (001) facetswere successfully synthesized in thepresenceofacationicpolymerunder fluoride‐freeconditions.Thecrystalshadhighphotocatalyticactivityandgoodrecyclability.

TiO2-P rich in (001) facets

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0

TiO2 -P P25

conventional TiO2C

/Co

T im e (m in)

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0