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2 Composites Science nd Technology 70 (2010) Contents lists ville t ScienceDirect Composites Science nd Technology journl homepge: Visile-light photoctlytic ctivity of semiconductor composites supported y electrospun fier Tieshi He,c, Zhengf Zhou, Weiing Xu, *, Yn Co, Zhifeng Shi, Wei-Ping Pn, ** School of Chemicl Engineering, Hefei University of Technology, Hefei , Chin Institute for Comustion Science nd Environmentl Technology, Western Kentucky University, Bowling Green, 42101, USA c Lioning Key Lortory of Applied Chemistry, Bohi University, Jinzhou , Chin rticle info strct Article history: Received 22 Jnury 2010 Accepted 2 My 2010 Aville online 19 My 2010 Keywords: A. Polymer mtrix composites (PMCs) B. Synergism D. Scnning/trnsmission electron microscopy (STEM) D. Thermo-grvimetric nlysis (TGA) E. Electro-spinning The preprtion nd photoctlysis of TiO 2 ZnS/fluoropolymer fier composites were investigted. The fluoropolymer nnofier mts with croxyl groups were prepred y electrospinning, nd then titnium nd zinc ions were introduced onto the fier surfces y the coordinting of croxyl of fluoropolymer in solution. The TiO 2 ZnS composites with dimeters 15 nm to 1 lm were immoilized on the surfce of fluoropolymer electrospun fier using hydrotherml synthesis. The Fourier trnsform infrred spectroscopy nd X-ry photoelectron spectroscopy nlysis revel tht some chemicl interction exists etween TiO 2 ZnS composites nd fluoropolymer fiers, so the semiconductor composites were immoilized tightly on the surfce of fluoropolymer fiers. The ultrviolet visile sorption spectr show the TiO 2 ZnS/fluoropolymer fier composites hve low nd gp nd good visile-light response ility. The degrdtion rte of methylene lue in TiO 2 ZnS/fluoropolymer fier composites system ws considerly higher thn tht of TiO 2 or TiO 2 ZnS nnoprticles system under visile-light irrdition, ecuse the TiO 2 ZnS/fluoropolymer fier composites possess good visile-light response ility, high specific surfce res, nd dsorption migrtion photodegrdtion process. The photoctlytic ctivity of TiO 2 ZnS/fluoropolymer fier composites chnges indistinctively fter 10 repeting photoctlysis tests. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction * Corresponding uthor. Tel./fx: ** Corresponding uthor. Tel.: E-mil ddresses: xw105105@sin.com (W. Xu), wei-ping.pn@wku.edu (W.-P. Pn). Growing concerns over the thret of chemicl wrfre gents nd exposure to toxic industril chemicls hve drwn much ttention to the chllenge of developing new hrmless tretment methods for the toxic orgnic mterils [1]. Photoctlytic degrdtion of hrmful orgnic pollutnts in the ir nd the wter using semiconductor prticles, such s titnium dioxide (TiO 2 ), is one of the most widely studied methods [2]. The semiconductor prticles re le to convert undnt solr energy into effective chemicl energy, nd minerlized the orgnic pollutnts completely [3]. However, the photoctlytic degrdtion of toxic orgnic pollutnts using semiconductor is still chllenged, in terms of the low photoctlytic efficiency under nturl sunlight, esy gglomerting nd losing in the using. Immoiliztion of semiconductor prticles on the crrier is one of the est effective methods to prevent the gglomerting nd losing of semiconductor prticles in using [4]. The semiconductor prticles directly depositing onto polymer electrospun fiers re lso used to prepre photoctlytic mterils [5]. However, polymers usully hve troules in compounding with inorgnic powders, nd esy re degrded in the photoctlytic process [6]. Fluoropolymers like poly(vinylidene difluoride) (PVDF), which hs excellent wether, rdition, chemicl nd therml resistnce due to stle C F ond in the min chin [7]. The fluoropolymers electrospun fier mts with micro-sized porous structure [8] re le to offer high specific re nd good enrichment ility for orgnic compounds, re suitle s photoctlyst crrier [9]. The visile-light photoctlytic ctivity of solitry TiO 2 is le to improved gretly y doping it with other elements, nd the synthesis of nnocrystlline TiO 2 cpped ZnS under hydrotherml conditions is convent wy [10]. In this pper we demonstrte novel method to prepre visile-light photoctlytic ctivity TiO 2 ZnS prticles loded y fluoropolymer electrospun fier with croxyl groups under hydrotherml condition. The photoctlytic ctivity nd stility were investigted through degrdtion of methylene lue using TiO 2 ZnS/fluoropolymer fier composites s photoctlyst under visile-light rdition. The results show the s-prepred composites hve good visile-light photoctlytic ctivity nd stility for the potentil pplicility in environmentl remedition /$ - see front mtter Ó 2010 Elsevier Ltd. All rights reserved. doi: /j.compscitech

3 1470 T. He et l. / Composites Science nd Technology 70 (2010) Experimentl Trifluoroethyl crylte (TFA) ws otined from Xueji Fluorine-silicon Chemicl Co., Ltd, Hrin Chin. Antse Deguss P25 ws purchsed from Shnghi Hiyi Scientific & Trding Co., Ltd. Poly(vinylidene difluoride) (PVDF), titnium oxo-sulphte (TiOS- O 4 ), methcrylic cid (MAA), zinc sulfte (ZnSO 4 ), thiocetmide (TAA), methylene lue, ure nd other chemicls were purchsed from Shnghi Chemicls Ltd., nd used s received. Perkin Elmer Spectrum 100 FTIR spectrometer ws used to widely scn the synthetic products. JSM-6700F scnning electron microscopy (SEM) ws utilized to study the surfce morphologies of the products. The specific surfce re (BET) nlyzed y ASAP 2020 M + C. ESCALAB 250 X-ry photoelectron spectroscopy (XPS) ws used to study the structure of composites. Trnsmission electron microscope (TEM) imge nd the selected re electron diffrction (SAED) pttern were tken on JEOL The crystl structure ws detected through the X-ry diffrction (XRD), Rigku D/mx-rB. The thermo-grvimetric nlysis (TGA), Netzsch TG- 209-F3, ws pplied to estimte the weight loss of composites. Ultrviolet visile (UV/VIS) sorption spectr were otined on Shimdzu Solidspec-3700 DUV spectrophotometer t room temperture. The synthesis of MAA TFA rndom copolymers ws performed in n utomted rector system. 30 g MAA, 70 g TFA, nd 0.5 g 2, 2-zoisisoutyronitrile (AIBN) were dded into three-necked flsk cpcity 250 ml equipped with condenser, stirrer nd N 2 inlet. After polymerizing t 80 C for 1 h, the rection mixture ws trnsferred to stinless steel plte nd plced in n oven t 40 C for 12 h. Then the rection mixture ws mintined t 100 C for 3 h, so tht the remining monomers cn polymerize. Poly(MAA-co-TFA)/PVDF electrospun fier mts were prepred using typicl electrospinning process [11] g PVDF nd 1.7 g poly(maa-co-tfa) were first dissolved in 88 g N,N-dimethylformmide (DMF). The solution ws electrospun t 25 kv positive voltge, 15 cm working distnce (the distnce etween the needle tip nd the trget), nd 1.0 ml h 1 flow rte. The collection time ws set to 2.0 h. All mnipultions were crried out t room temperture. The electrospun fier mts of fluoropolymers were cut into strips of dimension 2.0 cm 2.0 cm for the following experiments. The ove-mentioned strip of fluoropolymer electrospun fier mts were immersed into 10.0 ml, 0.08 mol L 1 queous solution of titnium oxo-sulphte nd 1.0 ml concentrted sulfuric cid in 50 ml Teflon-lined stinless steel utoclve for 6 h in order to form the complex of croxylic of fluoropolymer electrospun fier surfce nd titnium ion. Then 20.0 ml, 0.08 mol L 1 ure nd 20 ml distilled wter were dded. Then 0.0 ml, 0.5 ml, 1.0 ml, 3.0 ml, 5.0 ml, 0.01 mol L 1 ZnSO 4 nd corresponding 0.02 mol L 1 TAA were dded. The rectnt content of hydrotherml system ws shown in Tle 1. The utoclve ws seled t 150 C for 8 h, nd then cooled to room temperture. The TiO 2 ZnS/fluoropolymer fier composites were wshed for three times with distilled wter under ultrsonic to remove the unrected precursor nd yproducts, nd dried in vcuum t 80 C for 12 h. Tle 1 Rectnts content of hydrotherml system. Smples ZnSO 4 (10 2 mol) TiOSO 4 (10 2 mol) EDX of Zn (wt.%) Crystllite size (nm) TiZn TiZn TiZn TiZn TiZn Photoctlytic degrdtion of methylene lue solution ws performed y photochemicl rector (SGY-1, Stonetech Co., Ltd. Nnjing, Chin), light source is 350 W xenon lmp, nd rection system temperture ws 23 ± 1 C. The TiO 2 ZnS/fluoropolymer fier composites nd ml 16.0 mg L 1 methylene lue were dded to the qurtz tue-500 ml. The TiO 2 ZnS/fluoropolymer fier composites cn e extended well in methylene lue solution without stirring. The Deguss P25 nd TiO 2 ZnS powders synthesized ccording to Stengl et l. methods [10] were performed s stted in the previous steps with electromgnetic stirring. Prior to irrdition, the photoctlytic rection system ws stirred in drk condition for 15 min to estlish n dsorption desorption equilirium. The photoctlytic rection system ws smpled t regulr intervls, nd the semiconductor powders suspensions were centrifuged efore mesured. The remining methylene lue concentrtion fter dsorption desorption equilirium (C 0 ) nd photodegrdtion (C) ws detected y UV/VIS t 665 nm, nd the degrdtion efficiency e expressed s (C/C 0 )%. 3. Results nd discussion 3.1. Morphology of TiO 2 ZnS/fluoropolymer fier composites The poly(maa-co-tfa)/pvdf electrospun fier mts were mde of rndom nonwoven mesh of fiers, nd hd n interconnected open porous structure, s shown in Fig. 1. The SEM imges of TiO 2 ZnS/fluoropolymer fier composites prepred y different proportions for 8 h t 150 C re compred in Fig. 1 f nd the corresponding Zn content of composites is presented in Tle 1. The size distriution of semiconductor prticles ws out 5 nm to 1 lm, nd the size nd gglomertion of semiconductor prticles were improved with the incresing zinc ion contents in the rection system, s shown in Tle 1. The resons re le to explined s follows: the sulfide ion ws relesed from TAA t low temperture with high rte [12], ut the TiO 2 crystl prepred y hydrotherml hydrolysis of titnium oxo-sulphte with ure need multi-step rection [13], therefore the genertion nd growth of ZnS crystl were fster thn tht of the TiO 2 crystl under the sme rection system. Without zinc dded, the TiO 2 crystls formtion nd growth were controlled y croxyl long the surfce of electrospun fier, nd the out 5 nm TiO 2 fluoropolymer fier composites were chieved, s shown in Fig. 1. With the zinc ion dded, the ZnS crystls generted on the fier surfce preceded TiO 2 crystls, nd then oth semiconductor crystls decomposing nd comining, so the TiO 2 ZnS mixed crystls generted on the fluoropolymer fier surfce. When the zinc ion content of rection system is low, the TiO 2 ZnS prticle size is less thn 100 nm ecuse of heterogeneous nucletion effect, s shown in Fig. 1c nd d. With zinc ion content increse, ZnS homogeneous nucletion plys s dominnt role, plus, the nucletion nd growth of ZnS prticles ccelertes under hydrotherml conditions, which inhiits instnt decomposing nd comining of semiconductor prticles, thus semiconductor gglomertions sized over 200 nm were otined, s shown in Fig. 1e nd f Chrcteriztion of TiO 2 ZnS/fluoropolymer fier composites The XRD ptterns nd the corresponding chrcteristic 2h vlues of the diffrction peks were shown in Fig. 2. It is confirmed tht semiconductor composites s-prepred smples is identified s ntse-phse (JCPDS crd No ), ZnS s cuic-phse (JCPDS crd No ) nd the typicl PVDF crystl structure [14]. Three intensity peks only of TiO 2 or ZnS hve ppered in the XRD ptterns nd ll other high ngle peks hve sumerged in the ckground due to lrge line rodening. The crystl

4 T. He et l. / Composites Science nd Technology 70 (2010) Fig. 1. SEM imges of () poly(maa-co-tfa)/pvdf electrospun fier mts, nd TiO 2 ZnS/fluoropolymer fier composites prepred y different rectnts. () TiZn 0, (c) TiZn 1, (d) TiZn 2, (e) TiZn 3, (f) TiZn 4. Intensity f e d c Thet (Deg.) Fig. 2. XRD ptterns of () poly(maa-co-tfa)/pvdf electrospun fier nd the TiO 2 ZnS/fluoropolymer fier composites prepred y different rectnts. () TiZn 0, (c) TiZn 1, (d) TiZn 2, (e) TiZn 3, (f) TiZn 4. structure nd figurtion of semiconductor composites were further discussed using TEM nlysis. The TEM imges of TiO 2 ZnS/fluoropolymer fier composites prepred y rectnts TiZn 2 demonstrte the slightly gglomerted TiO 2 ZnS prticles, which re inclusive of nnocrystllites with indistinct polygonl shpe of out 100 nm in size, s shown in Fig. 2. The selected re electron diffrction (SAED) ptterns of cuic ZnS nd ntse TiO 2 re shown in Fig. 3 nd c. Typicl FTIR spectr of poly(maa-co-tfa)/pvdf electrospun fier nd TiO 2 ZnS/fluoropolymer fier composites prepred y rectnts TiZn 2 re compred in Fig. 4. It is evident tht the poly(- MAA-co-TFA)/PVDF electrospun fier mts hve peks t 3350 nd 1670 cm 1, corresponding to hydroxyl nd cronyl stretching of the croxyl groups of poly(maa-co-tfa). The corresponding hydroxyl nd cronyl sorption peks of TiO 2 ZnS/ fluoropolymer fier composites hve een rodened nd slightly

5 1472 T. He et l. / Composites Science nd Technology 70 (2010) Fig. 3. TEM imges of () TiO 2 ZnS/fluoropolymer fier composites prepred y rectnts TiZn 2, SAED of the smple () ZnS nd (c) TiO 2. shift to the low wvenumer. This my e due to tht the metl ion ws complextion dsored y the croxyl on the surfce of fluoropolymer electrospun [15,16], nd then the semiconductor nuclei formed nd grew into compound prticles on the surfce of fluoropolymer fier y hydrotherml precipittion, so the chemicl interction exists etween fluoropolymer fier nd semiconductor prticles. The surfce properties of TiO 2 ZnS/fluoropolymer fier composites were further investigted y XPS nlysis, s shown in Fig. 5. The Ti2p 3/2 onding energy is nd hs 0.6 ev shift compred with the typicl ntse TiO 2 (459.2 ev) [17], which resulted from the interction etween semiconductor prticles nd fluoropolymer [18], s shown in Fig. 5. There re peks ppered t round ev, ev, ev, in the C 1s spectrum nd T / % Wvenumers / cm -1 Fig. 4. FTIR spectr of () poly(maa-co-tfa)/pvdf electrospun fier, () TiO 2 ZnS/ fluoropolymer fier composites prepred y rectnts TiZn ev, ev in the O 1s spectrum, shown in Fig. 5 nd c, nd the peks were lso le to scrie to the influence of croxyl coordinted with nononding metl ion of semiconductor [19]. As result, the semiconductor prticles were le to immoilize tightly on the surfce of fluoropolymer fiers. UV/Vis spectr show the photosensitive properties of TiO 2 /ZnS fluoropolymer fier composites. The poly(maa-co-tfa)/pvdf electrospun fier mts hve no evident sorption ove 250 nm wvenumers (Fig. 6). This revels the poly(maa-co-tfa)/pvdf electrospun fier mts do not distur the light sorption of semiconductor of TiO 2 /ZnS fluoropolymer fier composites during the photoctlytic process. The UV/Vis sorption spectrum of the TiO 2 fluoropolymer fier composites reflects tht the sorption edge is out 382 nm, s shown in Fig. 6. The UV/Vis sorption edge of TiO 2 ZnS/fluoropolymer fier composites hve oviously shift to the long wvelength, s shown in Fig. 6c f. It is due to the S of ZnS surfce chnge the light sorption chrcter of TiO 2 ZnS, reduce the nd gp, [20] nd result in the improvement of the visile-light response ility of TiO 2 ZnS/fluoropolymer fier composites. When the rection system hve lower content zinc ion, the TiO 2 crystls were compounded nd mixed very well with ZnS through heterogeneous nucletion, nd the TiO 2 ZnS prticles hve strong compound effect, therefore the respectively sorption edge is out 473 nm nd 450 nm, s shown in Fig. 6c nd d. However, with the zinc ion content of rection system incresed, the ZnS gglomertion genertion, nd ZnS crystls were hrd to decompose for TiO 2 crystls comining, so the TiO 2 crystls re not cpped very well with ZnS crystls, therefore the compound effect reduces, the respectively sorption edge is out 402 nm nd 390 nm, s shown in Fig. 6e nd f. TGA curve of poly(maa-co-tfa)/pvdf electrospun fier shows severl therml decomposition stges, ut TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2 does not show therml decomposition stge until 450 C, s shown in Fig. 7. This phenomenon my e due to tht the low-moleculr weight sustnces of poly(maa-co-tfa)/pvdf electrospun fier mts dissolved or fused connected under long-time hydrotherml condition, nd the interction etween semiconductors prticles nd fluoropolymer fiers my lso improve the therml stility of TiO 2 ZnS/fluoropolymer

6 T. He et l. / Composites Science nd Technology 70 (2010) Reltive Intensity (cps) x Zn 2p F 1s O 1s Ti 2p C 1s S 2p Binding Energy (ev) C 1s c O 1s Intensity (cps) Intensity (cps) Binding Energy (ev) Binding Energy (ev) Fig. 5. XPS spectrum of TiO 2 ZnS/fluoropolymer fier composites prepred y rectnts TiZn 2 () survge, () C 1s, (c) O 1s Asornce Wvelength nm Fig. 6. UV/VIS sorption spectr of () poly(maa-co-tfa)/pvdf electrospun fier mts, nd the TiO 2 ZnS/fluoropolymer fier composites prepred y different rectnts () TiZn 0, (c) TiZn 1, (d) TiZn 2, (e) TiZn 3, (f) TiZn 4. fier composites. Semiconductor prticles content of TiO 2 ZnS/fluoropolymer fier composites ws mesured though the weight loss fter fluoropolymer electrospun fier ws fully decomposed t 700 C, nd the TiO 2 ZnS content of TiO 2 ZnS/fluoropolymer fier composites clculted ws 24.9%. The specific surfce re of TiO 2 ZnS of TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2 is considerly higher thn tht of Deguss P25 nd poly(maa-co-tfa)/pvdf electrospun fier mts, ut is lower thn tht of TiO 2 ZnS powders, s shown in Tle Photoctlytic degrdtion of methylene lue Photoctlysis of TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2, TiO 2 ZnS powders, Deguss P25, fluoropolymer d c e f Weight (%) Temperture ( 0 C) Fig. 7. Therml grvity nlyticl of () poly(maa-co-tfa)/pvdf electrospun fier mts nd () TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2. Tle 2 Specific surfce re. Smple SBET (m 2 g 1 ) Deguss P TiO 2 ZnS powders (MAA-co-TFA)/PVDF electrospun fier mts 37.2 TiO 2 ZnS of TiO 2 ZnS/fluoropolymer composites (TiZn 2 ) 96.7 electrospun fier mts nd lnk smple were performed for the methylene lue degrdtion under visile-light irrdition, s shown in Fig. 8. Ner-complete degrdtion of methylene lue occurred in 120 min in the presence of TiO 2 ZnS/fluoropolymer fier composites, s shown in Fig. 8. A slight chnge of the methylene

7 1474 T. He et l. / Composites Science nd Technology 70 (2010) C/C 0 (%) Time (min) Fig. 8. Photoctlytic degrdtion of methylene lue y () TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2, () TiO 2 ZnS powders, (c) Deguss P25, (d) (MAA-co-TFA)/PVDF electrospun fier mts; (e) lnk smple. e d c then migrted to semiconductor prticles surfce, finlly ws photoctlytic degrded y semiconductor prticles, so deduce the TiO 2 ZnS/fluoropolymer fier composites possess higher photoctlytic efficiency thn tht of TiO 2 ZnS powders for the degrdtion of methylene lue with the sme concentrtion. The photoctlytic stility of TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2 evluted y the degrdtion of methylene lue solution under 10 times of repeted visile-light irrdition for 120 min. The results revel tht the photoctlytic ctivity of TiO 2 ZnS/fluoropolymer fier composites chnges indistinctively. The SEM imge of TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2 fter 10 times degrdtion of methylene lue solution shows tht the semiconductor prticles re tightly immoilized on the surfce of fluoropolymer nnofiers fter the degrdtion tests. As conclusion, the TiO 2 ZnS/fluoropolymer fier composites possess high photoctlytic stility for the photodegrdtion of orgnic pollutnts Fig. 9. lue concentrtion ws oserved for the lnk smple, s shown in Fig. 8e. The remining methylene lue is 0.01 wt.% in the presence of TiO 2 ZnS/fluoropolymer fier composites, nd it is 75.6 wt.% in the presence of Deguss P25 fter 110 min visile-light irrdition, s shown in Fig. 8 nd c. So the TiO 2 ZnS/fluoropolymer fier composites exhiited higher photoctlytic efficiency thn tht of TiO 2 powder in the lmost sme TiO 2 concentrtion (Tle 3). The reson is tht the specific surfce re nd visile-light respond ility of TiO 2 ZnS/fluoropolymer fier composites were higher thn tht of Deguss P25 (Tle 2). The specific surfce re of TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2 ws lower of thn tht of TiO 2 ZnS powder, s shown in Tle 2, ut the remining methylene lue is 20.2 wt.% fter 110 min visile-light irrdition in the presence of TiO 2 ZnS powders. There my e dsorption migrtion photodegrdtion [21] exists in the photoctlysis rection: methylene lue ws first dsored onto the surfce of fluoropolymer fiers ecuse of its hydrophoicity, nd Tle 3 Photoctlyst concentrtion in solution. Smple Photoctlyst (mg L 1 ) TiO 2 ZnS/fluoropolymer fier composites (TiZn 2 ) 34.2 TiO 2 ZnS powders 34.7 Deguss P (MAA-co-TFA)/PVDF electrospun fier mts Blnk Fig. 9. SEM imge of TiO 2 ZnS/fluoropolymer fier composites prepred y TiZn 2 fter 10 times degrdtion of methylene lue solution under UV irrdition for 2.0 h ech. 4. Conclusion The TiO 2 ZnS composites with dimeters from 15 nm to 1 lm were immoilize on the surfce of fluoropolymer fier under different rection system, nd the chemicl interction existed etween TiO 2 ZnS composites nd fluoropolymer fiers. When the molr rtio of zinc ion nd titnic ion in rection system ws 1:80, the TiO 2 ZnS/fluoropolymer fier composites possess good visile-light photoctlytic ctivity ecuse of its strong visile-light response ctivity, quite high specific re nd synergistic effect. The repeted photoctlysis tests show the TiO 2 ZnS/fluoropolymer fier composites possess good visile-light photoctlytic stility. Acknowledgments This work is supported y the Ntionl Nturl Science Foundtion of Chin ( ), Doctorl Fund of Ministry of Eduction of Chin ( ). References [1] Co Y, Go Z, Zhu J, Wng Q, Hung Y, Chiu C, et l. Impcts of hlogen dditions on mercury oxidtion, in slipstrem selective ctlyst reduction (SCR), rector when urning su-ituminous col. 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