Electrospun polymeric nanofibrous composites containing TiO2 short nanofibers

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MaterialsChemistryandPhysics129 (2011) 701–704

ContentslistsavailableatScienceDirect

Materials

Chemistry

and

Physics

jo u r n al h om ep a ge : w w w . e l s e v i e r . c o m / l o c a t e / m a t c h e m p h y s

Materials

science

communication

Electrospun

polymeric

nanoﬁbrous

composites

containing

TiO

2

short

nanoﬁbers

Ali

E. Deniz,

Asli

Celebioglu,

Fatma

Kayaci,

Tamer

Uyar

∗

UNAM-InstituteofMaterialsScience&Nanotechnology,BilkentUniversity,Ankara,06800,Turkey

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• PolymericnanofibrouscompositescontaininganataseTiO2shortnanofibers(TiO2-SNF)wereproducedviaelectrospinning. • PMMA,PAN,PETandPCelectrospunnanofiberscontainingTiO2-SNFwereobtained.

• ThenanoﬁbrouscompositescontainingTiO2-SNFhasshownphotocatalyticactivity.

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Articlehistory:

Received19February2011

Receivedinrevisedform13May2011 Accepted12June2011 Keywords: Compositematerials Nanostructures Polymers Electronmicroscopy

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Inthisstudy,polymericnanofibrouscompositescontaininganataseTiO2shortnanofibers(TiO2-SNF) weresuccessfullyproducedviaelectrospinning.Thefabricationofthenanofibrouscompositestructure includestwosteps.First,anataseTiO2nanofiberswereobtainedbycalcinationofelectrospunPVP/TiO2 nanofibersandthencrushedintoshortnanofibersrangingfromfewmicronsinlength.Second,these TiO2-SNFweredispersedintopolymersolutionsandthenelectrospunintonanofibrouscomposites.We obtainednanofiberscontainingTiO2-SNFfromdifferentpolymertypesincludingPMMA,PAN,PETand PC.TheSEMandTEMimagingindicatedthatsomeoftheTiO2-SNFwerefullycoveredbythepolymeric matrixwhereassomeTiO2-SNFwerepartiallycoveredand/orstickonthesurfaceofthefibers.The photocatalyticactivityofnanofibrouscompositescontainingTiO2-SNFwasevaluatedbymonitoringthe photocatalyticdecompositionofamodeldye(rhodamine-6G)underUVirradiation.

1. Introduction

Functional nanoﬁbers can be easily produced from var-ious polymers, polymer blends, sol–gels, composites and metal oxides via electrospinning technique [1–8]. Electrospun nanoﬁbers/nanowebshaveseveralremarkablecharacteristicssuch asaverylargesurfaceareatovolumeratioandnanoporous fea-turesalongwithphysical,chemicalandsurfacefunctionalization

[1–8].Inaddition,itisfairlyeasytoimprovethefunctionalityof theelectrospunnanoﬁbersbyelectrospinningofpolymermatrix containing functional additives (e.g. nanoparticles) [2,3,9]. For instance,theincorporation ofmetaloxide nanoparticlessuchas TiO2 into electrospunpolymeric nanoﬁbers were reported and

itwasshownthatthesefunctionalnanoﬁbrouscompositeshave potentialstobeusedinﬁltrationsinceTiO2 nanoparticlesshow

photocatalyticactivityand arevery effectivefor degradationof organicpollutantsand/orkillingbacteria[10–13].Yet,theleaching ofnanoparticlesfromthesepolymericcompositesandtheir

recov-∗ Correspondingauthor.Tel.:+903122903571;fax:+903122664365. E-mailaddress:tamer@unam.bilkent.edu.tr(T.Uyar).

eryisalwaysanenvironmentalissue[14,15].Recently,ithasalso beenreportedthatelectrospunTiO2 shortnanoﬁbershavingfew

micrometersinlengthhaveshownbetterphotocatalyticactivity comparedtoTiO2nanoparticles[16].

In this study,we used TiO2 short nanoﬁbers(TiO2-SNF)for

producing polymeric nanoﬁbrous composite structures. These polymericnanoﬁberscontainingTiO2-SNFweresuccessfully

pro-duced via electrospinning with the goal to develop functional nanoﬁltrationmaterialssinceTiO2isknowntobeveryeffectivefor

degradationoforganicpollutantsduetoitsphotocatalytic activ-ity.WeelectrospunnanoﬁberscontainingTiO2-SNFfromdifferent

polymer types which are commonly used as ﬁltration materi-alssuchaspoly(methylmethacrylate)(PMMA),polyacrylonitrile (PAN),polyethyleneterephthalate(PET)andpolycarbonate(PC).As apreliminarystudy,thephotocatalyticactivityofPETnanoﬁbers containingTiO2-SNFwasinvestigatedforphotocatalytic

decom-positionofrhodamine-6GunderUVirradiation.Tothebestofour knowledge,thisistheveryfirstreportshowingthatmetaloxide shortnanofiberscan beincorporatedintopolymeric nanofibers viaelectrospinning.Suchnanofibrouscompositestructurescanbe obtainedfromdifferentpolymertypesand willbeapplicablein variousareasdependingonthepolymertypeandthefunctionof metaloxides.

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702 A.E.Denizetal./MaterialsChemistryandPhysics129 (2011) 701–704

Fig.1.(a)RepresentativeSEMimage,(b)and(c)EDXelementalmapsand(d)EDXspectrumofelectrospunTiO2nanoﬁbers,(e)SEMimageofTiO2-SNFobtainedafter

crushingtheelectrospunTiO2nanoﬁbers.

2. Experimentaldetails

2.1. Materials

Titanium(IV)-isopropoxide(97%,Aldrich),glacialaceticacid(100%,Merck), ethanol(≥99.8%, Sigma–Aldrich),dimethylformamide(DMF)(Riedel, Pestenal), tetrahydrofuran(THF)(≥99.5%,Sigma),dichloromethane(DCM)(≥99%,Sigma), triﬂuoroaceticacid(TFA)(99%,Sigma–Aldrich),polyvinylpyrrolidone(PVP,Mw ∼1,300,000,Aldrich),poly(methylmethacrylate)(PMMA)(Mw∼350,000,Aldrich), polyacrylonitrile(PAN)(donatedbyAKSACo.,Turkey),polyethyleneterephthalate (PET)(donatedbyKorteksCo.,Turkey),polycarbonate(PC)(Mw∼64,000,Aldrich) wereusedas-received.

2.2. PreparationofTiO2nanoﬁbers

Titanium(IV)-isopropoxide(2.88ml)precursorwasmixedwithglacialacetic acid(2ml)andethanol(2ml)solventsystem.Afterstirringfor10min,PVP(0.6g) dissolvedinethanol(3ml)wasaddedtothissolution.Theresultingmixturewas constantlystirredfor12h,andtheyellowishsol–gelwasobtained.ThePVP/TiO2

solprecursorwasplacedintoa1mlsyringehavingmetallicneedletip(inner diameter=0.4mm)forelectrospinning.Thesolutionwasfedbyasyringepump hor-izontally(Model:SP101IZ,WPI).Electricﬁeldwascomprisedbythehighvoltage powersupply(MatsusadaPrecision,AUSeries,Japan).Theelectrospinning param-eterswereasfollows:appliedvoltage=15kV,feedrate=0.5mlh−1_,_{tip-to-collector}

distance=10cm.Electrospunnanofibersweredepositedonagroundedstationary cylindricalmetalcollectorcoveredbyapieceofaluminumfoil.Theelectrospinning wascarriedoutinenclosedplexiglassboxandat23◦Cat26%relativehumidity.The electrospunnanofibersweredriedovernightunderthehoodandthencalcinatedat 500◦_C_for₃_h_in_an_oven_in_order_to_obtain_pure_TiO₂_nanofibers.

2.3. PreparationofpolymericnanoﬁberscontainingTiO2shortnanoﬁbers

TiO2shortnanoﬁbers(TiO2-SNF)rangingfrom∼1to∼10␮minlengthwere

obtainedbycrushingtheelectrospunTiO2nanoﬁbersinamortar.The

concentra-tionofthepolymersolutionsandtheelectrospinningparameterswereoptimized inordertogetbead-freeuniformﬁbers.Thepolymersolutionswerepreparedas follows:PMMAandPANweredissolvedinDMFusing12.5%(w/v)and20%(w/v) polymerconcentration,respectively.Inaddition,20%(w/v)PETwasdissolvedin TFA:DCM(1:1,v/v),while25%(w/v)PCwasdissolvedinTHF:DMF(3:2,v/v) sol-ventsystem.Then,6%TiO2-SNF(w/w,withrespecttopolymer)inPMMAand

2%TiO2-SNF(w/w,withrespecttopolymer)inPAN,PETandPCsolutionswere

dispersedbystirringfor1h.The%loadingofTiO2-SNFwasaffectingthe

electro-spinning,therefore,TiO2-SNFloadingwaschosenforeachpolymersolutionthat

didnotaffecttheelectrospinningofbead-freenanoﬁbers.Subsequently,PAN,PET, andPCsolutionswereelectrospunwiththefollowingparameters:applied volt-age=15kV,tip-to-collectordistance=10cmandfeedrate=1mlh−1.ForPMMA

Fig.2. XRDpatternofTiO2-SNF.

solutiontheparameterswereasfollows:appliedvoltage=10kV,tip-to-collector distance=15cmandfeedrate=1mlh−1_.

2.4. PhotocatalyticactivityofpolymericnanoﬁberscontainingTiO2short

nanoﬁbers

Thephotocatalyticactivitywasanalyzedbyphotodegradationof rhodamine-6G(Rh-6G)(2×10−5_M)_in_aqueous_medium._Electrospun_PET_nanoweb_containing

TiO2-SNF(PET-NF/TiO2-SNF)(weightofnanoweb:2mg,dimensionofthenanoweb:

1.0cm×1.0cm)wasputintoquartzcuvette(width:1cm,length:1cm,andheight: 5cm,Hellma)ﬁlledwithrhodamine-6Gsolution.Thecuvettewasplacedwitha distanceof5cmfromtheUVsource(8W,UVLMS-38EL)andkeptunderUV irra-diationat254nmwavelength.Atknowntimeintervals,thedyeconcentrationwas measuredbyusingUV-visspectrophotometer.DuringtheUV–vismeasurement,the PET-NF/TiO2-SNFnanowebwasﬂoatingonthetopofthedyesolutionandtherefore

thenanowebdidnotinterferewiththeUV–vismeasurement. 2.5. Measurementandcharacterization

Scanningelectron microscope (SEM) (FEI – Quanta 200 FEG) and trans-missionelectron microscope (TEM)(FEI – Tecnai G2F30) were usedfor the

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Fig.3.SEMimagesofnanofibrouscompositeswith(1)lowmagnificationand(2)highmagnification:(a1)and(a2)PMMA-NF/TiO2-SNF,(b1)and(b2)PAN-NF/TiO2-SNF,

(c1)and(c2)PET-NF/TiO2-SNFand(d1)and(d2)PC-NF/TiO2-SNF.

Fig.4. TEMimagesofthePMMA-NF/TiO2-SNFfromtwodifferentﬁbersshowingthat(a)theTiO2-SNFwasembeddedinthePMMAﬁbermatrixand(b)thesmallTiO2-SNF

wasembeddedandthelargeTiO2-SNFwasstickingoutfromthePMMAﬁbermatrix.TiO2-SNFwasvisualizedasadarkobjectintheTEMimage.

morphologicalinvestigationofthenanofibers.Thefiberdiameterrangeandthe averagefiberdiameterweredeterminedfromtheSEMimagesandaround100 fiberswereanalyzed.EnergydispersiveX-ray(EDX)wasperformedforthe ele-mentalanalysisoftheTiO2nanofibers.TheX-raydiffraction(XRD)patternforTiO2

nanoﬁberswereobtainedbyusingPANanalyticalX’PertPowderdiffractometerwith CuK␣radiationinarange2Â=10–75◦_._{UV–vis–NIR}_{spectrophotometer}_(Varian_Cary

5000)wasusedattherange400–600nmwavelengthtomonitorthephotocatalytic degradationofrhodamine-6Gdyesolution.

3. Resultsanddiscussion

Pure TiO2 nanoﬁbers were produced via electrospinning of

PVP/TiO2 sol precursor followedby removal oforganic

compo-nent(PVP)bycalcinationat500◦Cfor3h.Duringthecalcination process of PVP/TiO2, thematerial maintained its ﬁbrous

struc-tures and brittle TiO2 nanoﬁbers were obtained. The scanning

Fig.5.TheUV–visspectrumoftheRh-6GsolutioncontainingPET-NF/TiO2-SNF(a)asafunctionoftheUVirradiationtime,(b)therate(C/C0)ofRh-6Gdegradation.The

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704 A.E.Denizetal./MaterialsChemistryandPhysics129 (2011) 701–704

electronmicroscopy(SEM)andtheenergydispersiveX-ray(EDX) spectroscopyanalysesofTiO2nanoﬁberswereperformed(Fig.1).

Bead-free TiO2 nanoﬁbers having diameters in the range of

40–500nm with average ﬁber diameter of 200±120nm were obtained. The elemental mapping of TiO2 nanoﬁbers by EDX

showed that titanium and oxygen are the main elements of thenanoﬁbers(Fig.1(b)–(d)).Electrospun TiO2 nanoﬁberswere

crushed into short nanoﬁbers (TiO2-SNF) ranging from ∼1 to

∼10␮minlength(Fig.1(e)).

ThecrystallinestructureofTiO2-SNFwasidentiﬁedbyX-ray

diffraction(XRD).Fig.2hasshowntheXRDofTiO2-SNFwithseries

ofdiffractionpeakscorrespondingtoanatasephasewhichisknown foritsphotocatalyticactivity[17–19].Thesalientpeakat2Â=25.4◦ correspondstothe(101)planeoftheanataseTiO2structureand

theotherpeaksat2Â=38.1◦,48.4◦,54.3◦,55.3◦,63.0◦,69.1◦,70.3◦ correspondtothediffractionof(004),(200),(105),(211),(204), (116),and(220)planes,respectively[20].XRDpatternoftheTiO2

-SNFhasnodiffractionpeakat2Â=27.5◦whichischaracteristicfor therutile phasesignifying thatcalcinationprocessyieldedTiO2

nanoﬁbershavingpureanatasestructure.

Thefabricationofelectrospunpolymericnanoﬁbers contain-ing TiO2-SNF includes two steps. In the ﬁrst step, PVP/TiO2

electrospunnanoﬁberswerecalcinated in order toobtainpure anataseTiO2 nanoﬁbersand thentheywerecrushedintoshort

nanoﬁbers ranging from ∼1 to ∼10␮m in length (Fig. 1(e)). These TiO2-SNF were blended with polymer solutionand then

electrospunintonanofibrouscompositestructures.Inthisstudy, weelectrospunnanofibersfromseveraldifferentpolymertypes including poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN),polyethyleneterephthalate(PET) andpolycarbonate(PC) containingTiO2-SNF.Theseelectrospunnanofibrouscomposites

wereabbreviatedas:PMMA-NF/TiO2-SNF,PAN-NF/TiO2-SNF,

PET-NF/TiO2-SNFandPC-NF/TiO2-SNF.TherepresentativeSEMimages

ofthesenanoﬁbrouscompositesaredepictedinFig.3.Weobserved thattheincorporationofTiO2-SNFdidnotaffectthe

electrospin-ningofthesepolymersandbead-freenanofiberswereobtained inallcases.Wefurtheranalyzedthesenanofibrouscompositesby transmissionelectronmicroscopy(TEM).TherepresentativeTEM imagesofthePMMA-NF/TiO2-SNFcompositenanofibersaregiven

inFig.4.SEMandTEManalysesrevealedthatsomeoftheTiO2-SNF

werefullycoveredbythepolymericmatrixwhereassomeTiO2-SNF

werepresentonthesurfaceofthepolymericmatrixand/or stick-ingoutfromthepolymericmatrix.Asmentionedabove,TiO2-SNF

hasanatasestructurewhichisknownforitsphotocatalytic activ-ity.Asapreliminarystudy,wealsoinvestigatedthephotocatalytic activityofPET-NF/TiO2-SNF.

Thephotocatalyticdegradationofrhodamine-6G(Rh-6G)dye solutionwasusedasamodelphotoreaction,anditsdegradation wasfollowedbytheUV–vismeasurementofthesolution contain-ingPET-NF/TiO2-SNF.ThechangeintheabsorbanceontheUV–vis

spectrumoftheRh-6GsolutioncontainingPET-NF/TiO2-SNFasa

functionoftheUVirradiationtimeisshowninFig.5.Thechangeof theabsorptionpeakpointofRh-6Gat526nmwasusedfor calcu-latingtherate(C/C0)ofRh-6GdegradationwhereC0andCindicate

theinitialconcentrationofRh-6GbeforeUVirradiationandafterUV irradiationattimet,respectively.AsthephotodegradationofRh-6G

occurredwithrespecttoUVirradiationtime,theabsorbanceofthe Rh-6GsolutionintheUV–visspectrumdecreasedgradually,and theredcolorofthesolutiondisappearedtotallyafter24hofUV irra-diationindicatingthatalmost100%oftheRh-6Gwasdecomposed. ThisresultconﬁrmedthephotocatalyticdegradationofRh-6Gby PET-NF/TiO2-SNFnanoﬁbrouscomposite.

4. Conclusion

Here,wesummarizedtheproductionofpolymericnanoﬁbrous compositescontaininganataseTiO2 shortnanoﬁbers(TiO2-SNF)

viaelectrospinningtechnique.Wehaveshownthat nanoﬁbrous compositescontainingTiO2-SNFfromdifferentpolymerssuchas

PMMA,PAN,PETandPCcaneasilybeobtainedvia electrospin-ning.TheSEMandTEMstudiesrevealedthatsomeTiO2-SNFwere

fullyinside thepolymericmatrix whereassomeTiO2-SNFwere

partiallycoveredandstickontheﬁbersurface.Thephotocatalytic activityofthesenanoﬁbrouscompositescontainingTiO2-SNFwas

evaluatedbythephotocatalyticdecompositionofrhodamine-6G underUVirradiation.Ourpreliminaryresultsindicatedthatthese nanoﬁbrouscompositeshavephotocatalyticactivityandcouldbe usefulfortreatmentoforganicpollutants.Moreover,such nanoﬁ-brouscompositestructurescanalsobeapplicableinotherareas dependingonthepolymertypeandthefunctionofmetaloxides.

Acknowledgements

StatePlanningOrganization(DPT)ofTurkeyisacknowledged forthesupportofUNAM-InstituteofMaterialsScienceand Nano-technology. Dr. Uyar acknowledges Marie Curie International Reintegration Grant (IRG) for funding NANOWEB (PIRG06-GA-2009-256428) project. A. Celebioglu and F. Kayaci thank to TUBITAK-BIDEBfornationalgraduatestudyscholarships.

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