Visible-light photocatalytic activity of semiconductor composites supported by electrospun fiber

Composites Science and Technology 70 (2010) 1469–1475

Contents lists available at ScienceDirect

Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech

Visible-light photocatalytic activity of semiconductor composites supported by electrospun fiber Tieshi He a,c, Zhengfa Zhou a, Weibing Xu a,*, Yan Cao b, Zhifeng Shi a, Wei-Ping Pan b,** a

School of Chemical Engineering, Hefei University of Technology, Hefei 230009, China Institute for Combustion Science and Environmental Technology, Western Kentucky University, Bowling Green, 42101, USA c Liaoning Key Laboratory of Applied Chemistry, Bohai University, Jinzhou 121000, China b

a r t i c l e

i n f o

Article history: Received 22 January 2010 Accepted 2 May 2010 Available online 19 May 2010 Keywords: A. Polymer–matrix composites (PMCs) B. Synergism D. Scanning/transmission electron microscopy (STEM) D. Thermo-gravimetric analysis (TGA) E. Electro-spinning

a b s t r a c t The preparation and photocatalysis of TiO2–ZnS/fluoropolymer fiber composites were investigated. The fluoropolymer nanofiber mats with carboxyl groups were prepared by electrospinning, and then titanium and zinc ions were introduced onto the fiber surfaces by the coordinating of carboxyl of fluoropolymer in solution. The TiO2–ZnS composites with diameters 15 nm to 1 lm were immobilized on the surface of fluoropolymer electrospun fiber using hydrothermal synthesis. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis reveal that some chemical interaction exists between TiO2–ZnS composites and fluoropolymer fibers, so the semiconductor composites were immobilized tightly on the surface of fluoropolymer fibers. The ultraviolet–visible absorption spectra show the TiO2–ZnS/fluoropolymer fiber composites have low band gap and good visible-light response ability. The degradation rate of methylene blue in TiO2–ZnS/fluoropolymer fiber composites system was considerably higher than that of TiO2 or TiO2–ZnS nanoparticles system under visible-light irradiation, because the TiO2–ZnS/fluoropolymer fiber composites possess good visible-light response ability, high specific surface areas, and adsorption–migration–photodegradation process. The photocatalytic activity of TiO2–ZnS/fluoropolymer fiber composites changes indistinctively after 10 repeating photocatalysis tests. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Growing concerns over the threat of chemical warfare agents and exposure to toxic industrial chemicals have drawn much attention to the challenge of developing new harmless treatment methods for the toxic organic materials [1]. Photocatalytic degradation of harmful organic pollutants in the air and the water using semiconductor particles, such as titanium dioxide (TiO2), is one of the most widely studied methods [2]. The semiconductor particles are able to convert abundant solar energy into effective chemical energy, and mineralized the organic pollutants completely [3]. However, the photocatalytic degradation of toxic organic pollutants using semiconductor is still challenged, in terms of the low photocatalytic efficiency under natural sunlight, easy agglomerating and losing in the using. Immobilization of semiconductor particles on the carrier is one of the best effective methods to prevent the agglomerating and losing of semiconductor particles in using [4]. The semicon-

* Corresponding author. Tel./fax: +86 551 2901455. ** Corresponding author. Tel.: +1 270 7452221. E-mail addresses: [email protected] (W. Xu), [email protected] (W.-P. Pan). 0266-3538/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2010.05.001

ductor particles directly depositing onto polymer electrospun fibers are also used to prepare photocatalytic materials [5]. However, polymers usually have troubles in compounding with inorganic powders, and easy are degraded in the photocatalytic process [6]. Fluoropolymers like poly(vinylidene difluoride) (PVDF), which has excellent weather, radiation, chemical and thermal resistance due to stable –C–F bond in the main chain [7]. The fluoropolymers electrospun fiber mats with micro-sized porous structure [8] are able to offer high specific area and good enrichment ability for organic compounds, are suitable as photocatalyst carrier [9]. The visible-light photocatalytic activity of solitary TiO2 is able to improved greatly by doping it with other elements, and the synthesis of nanocrystalline TiO2 capped ZnS under hydrothermal conditions is a convent way [10]. In this paper we demonstrate a novel method to prepare visible-light photocatalytic activity TiO2–ZnS particles loaded by fluoropolymer electrospun fiber with carboxyl groups under hydrothermal condition. The photocatalytic activity and stability were investigated through degradation of methylene blue using TiO2–ZnS/fluoropolymer fiber composites as photocatalyst under visible-light radiation. The results show the as-prepared composites have good visible-light photocatalytic activity and stability for the potential applicability in environmental remediation.

1470

T. He et al. / Composites Science and Technology 70 (2010) 1469–1475

2. Experimental Trifluoroethyl acrylate (TFA) was obtained from Xuejia Fluorine-silicon Chemical Co., Ltd, Harbin China. Anatase Degussa P25 was purchased from Shanghai Haiyi Scientific & Trading Co., Ltd. Poly(vinylidene difluoride) (PVDF), titanium oxo-sulphate (TiOSO4), methacrylic acid (MAA), zinc sulfate (ZnSO4), thioacetamide (TAA), methylene blue, urea and other chemicals were purchased from Shanghai Chemicals Ltd., and used as received. Perkin Elmer Spectrum 100 FTIR spectrometer was used to widely scan the synthetic products. JSM-6700F scanning electron microscopy (SEM) was utilized to study the surface morphologies of the products. The specific surface area (BET) analyzed by ASAP 2020 M + C. ESCALAB 250 X-ray photoelectron spectroscopy (XPS) was used to study the structure of composites. Transmission electron microscope (TEM) image and the selected area electron diffraction (SAED) pattern were taken on JEOL 2010. The crystal structure was detected through the X-ray diffraction (XRD), Rigaku D/max-rB. The thermo-gravimetric analysis (TGA), Netzsch TG209-F3, was applied to estimate the weight loss of composites. Ultraviolet–visible (UV/VIS) absorption spectra were obtained on a Shimadzu Solidspec-3700 DUV spectrophotometer at room temperature. The synthesis of MAA–TFA random copolymers was performed in an automated reactor system. 30 g MAA, 70 g TFA, and 0.5 g 2, 2-azobisisobutyronitrile (AIBN) were added into a three-necked flask capacity 250 mL equipped with a condenser, a stirrer and a N2 inlet. After polymerizing at 80 °C for 1 h, the reaction mixture was transferred to a stainless steel plate and placed in an oven at 40 °C for 12 h. Then the reaction mixture was maintained at 100 °C for 3 h, so that the remaining monomers can polymerize. Poly(MAA-co-TFA)/PVDF electrospun fiber mats were prepared using a typical electrospinning process [11]. 10.3 g PVDF and 1.7 g poly(MAA-co-TFA) were first dissolved in 88 g N,N-dimethylformamide (DMF). The solution was electrospun at 25 kV positive voltage, 15 cm working distance (the distance between the needle tip and the target), and 1.0 mL h 1 flow rate. The collection time was set to 2.0 h. All manipulations were carried out at room temperature. The electrospun fiber mats of fluoropolymers were cut into strips of dimension 2.0 cm  2.0 cm for the following experiments. The above-mentioned strip of fluoropolymer electrospun fiber mats were immersed into 10.0 mL, 0.08 mol L 1 aqueous solution of titanium oxo-sulphate and 1.0 mL concentrated sulfuric acid in a 50 mL Teflon-lined stainless steel autoclave for 6 h in order to form the complex of carboxylic of fluoropolymer electrospun fiber surface and titanium ion. Then 20.0 mL, 0.08 mol L 1 urea and 20 mL distilled water were added. Then 0.0 mL, 0.5 mL, 1.0 mL, 3.0 mL, 5.0 mL, 0.01 mol L 1 ZnSO4 and corresponding 0.02 mol L 1 TAA were added. The reactant content of hydrothermal system was shown in Table 1. The autoclave was sealed at 150 °C for 8 h, and then cooled to room temperature. The TiO2–ZnS/fluoropolymer fiber composites were washed for three times with distilled water under ultrasonic to remove the unreacted precursor and byproducts, and dried in vacuum at 80 °C for 12 h.

Photocatalytic degradation of methylene blue solution was performed by photochemical reactor (SGY-1, Stonetech Co., Ltd. Nanjing, China), light source is 350 W xenon lamp, and reaction system temperature was 23 ± 1 °C. The TiO2–ZnS/fluoropolymer fiber composites and 300.0 mL 16.0 mg L 1 methylene blue were added to the quartz tube-500 mL. The TiO2–ZnS/fluoropolymer fiber composites can be extended well in methylene blue solution without stirring. The Degussa P25 and TiO2–ZnS powders synthesized according to Stengl et al. methods [10] were performed as stated in the previous steps with electromagnetic stirring. Prior to irradiation, the photocatalytic reaction system was stirred in a dark condition for 15 min to establish an adsorption–desorption equilibrium. The photocatalytic reaction system was sampled at regular intervals, and the semiconductor powders suspensions were centrifuged before measured. The remaining methylene blue concentration after adsorption–desorption equilibrium (C0) and photodegradation (C) was detected by UV/VIS at 665 nm, and the degradation efficiency be expressed as (C/C0)%. 3. Results and discussion 3.1. Morphology of TiO2–ZnS/fluoropolymer fiber composites The poly(MAA-co-TFA)/PVDF electrospun fiber mats were made of random nonwoven mesh of fibers, and had an interconnected open porous structure, as shown in Fig. 1a. The SEM images of TiO2–ZnS/fluoropolymer fiber composites prepared by different proportions for 8 h at 150 °C are compared in Fig. 1b–f and the corresponding Zn content of composites is presented in Table 1. The size distribution of semiconductor particles was about 5 nm to 1 lm, and the size and agglomeration of semiconductor particles were improved with the increasing zinc ion contents in the reaction system, as shown in Table 1. The reasons are able to explained as follows: the sulfide ion was released from TAA at low temperature with high rate [12], but the TiO2 crystal prepared by hydrothermal hydrolysis of titanium oxo-sulphate with urea need multi-step reaction [13], therefore the generation and growth of ZnS crystal were faster than that of the TiO2 crystal under the same reaction system. Without zinc added, the TiO2 crystals formation and growth were controlled by carboxyl along the surface of electrospun fiber, and the about 5 nm TiO2–fluoropolymer fiber composites were achieved, as shown in Fig. 1b. With the zinc ion added, the ZnS crystals generated on the fiber surface preceded TiO2 crystals, and then both semiconductor crystals decomposing and combining, so the TiO2–ZnS mixed crystals generated on the fluoropolymer fiber surface. When the zinc ion content of reaction system is low, the TiO2–ZnS particle size is less than 100 nm because of heterogeneous nucleation effect, as shown in Fig. 1c and d. With zinc ion content increase, ZnS homogeneous nucleation plays as a dominant role, plus, the nucleation and growth of ZnS particles accelerates under hydrothermal conditions, which inhibits instant decomposing and combining of semiconductor particles, thus semiconductor agglomerations sized over 200 nm were obtained, as shown in Fig. 1e and f. 3.2. Characterization of TiO2–ZnS/fluoropolymer fiber composites

Table 1 Reactants content of hydrothermal system. Samples

ZnSO4 (10 mol)

TiZn0 TiZn1 TiZn2 TiZn3 TiZn4

0.0 0.5 1.0 3.0 5.0

2

TiOSO4 (10 mol) 80 80 80 80 80

2

EDX of Zn (wt.%)

Crystallite size (nm)

0.0 0.24 0.91 4.73 13.06

5 15 100 200 1000

The XRD patterns and the corresponding characteristic 2h values of the diffraction peaks were shown in Fig. 2. It is confirmed that semiconductor composites as-prepared samples is identified as anatase-phase (JCPDS card No. 21-1272), ZnS as cubic-phase (JCPDS card No. 5-566) and the typical PVDF crystal structure [14]. Three intensity peaks only of TiO2 or ZnS have appeared in the XRD patterns and all other high angle peaks have submerged in the background due to large line broadening. The crystal

T. He et al. / Composites Science and Technology 70 (2010) 1469–1475

1471

Intensity

Fig. 1. SEM images of (a) poly(MAA-co-TFA)/PVDF electrospun fiber mats, and TiO2–ZnS/fluoropolymer fiber composites prepared by different reactants. (b) TiZn0, (c) TiZn1, (d) TiZn2, (e) TiZn3, (f) TiZn4.

f e d c b a 30

40

50

60

2 Theata (Deg.) Fig. 2. XRD patterns of (a) poly(MAA-co-TFA)/PVDF electrospun fiber and the TiO2– ZnS/fluoropolymer fiber composites prepared by different reactants. (b) TiZn0, (c) TiZn1, (d) TiZn2, (e) TiZn3, (f) TiZn4.

structure and figuration of semiconductor composites were further discussed using TEM analysis. The TEM images of TiO2–ZnS/fluoropolymer fiber composites prepared by reactants TiZn2 demonstrate the slightly agglomerated TiO2–ZnS particles, which are inclusive of nanocrystallites with indistinct polygonal shape of about 100 nm in size, as shown in Fig. 2a. The selected area electron diffraction (SAED) patterns of cubic ZnS and anatase TiO2 are shown in Fig. 3b and c. Typical FTIR spectra of poly(MAA-co-TFA)/PVDF electrospun fiber and TiO2–ZnS/fluoropolymer fiber composites prepared by reactants TiZn2 are compared in Fig. 4. It is evident that the poly(MAA-co-TFA)/PVDF electrospun fiber mats have peaks at 3350 and 1670 cm 1, corresponding to hydroxyl and carbonyl stretching of the carboxyl groups of poly(MAA-co-TFA). The corresponding hydroxyl and carbonyl absorption peaks of TiO2–ZnS/ fluoropolymer fiber composites have been broadened and slightly

1472

T. He et al. / Composites Science and Technology 70 (2010) 1469–1475

Fig. 3. TEM images of (a) TiO2–ZnS/fluoropolymer fiber composites prepared by reactants TiZn2, SAED of the sample (b) ZnS and (c) TiO2.

shift to the low wavenumber. This may be due to that the metal ion was complexation adsorbed by the carboxyl on the surface of fluoropolymer electrospun [15,16], and then the semiconductor nuclei formed and grew into compound particles on the surface of fluoropolymer fiber by hydrothermal precipitation, so the chemical interaction exists between fluoropolymer fiber and semiconductor particles. The surface properties of TiO2–ZnS/fluoropolymer fiber composites were further investigated by XPS analysis, as shown in Fig. 5. The Ti2p3/2 bonding energy is 458.6 and has 0.6 eV shift compared with the typical anatase TiO2 (459.2 eV) [17], which resulted from the interaction between semiconductor particles and fluoropolymer [18], as shown in Fig. 5a. There are peaks appeared at around 282.3 eV, 286.5 eV, 288.7 eV, in the C1s spectrum and

a 3350

b

T/%

1670

4000 3000 2000 2000

1500

1000

500

Wavenumbers / cm -1 Fig. 4. FTIR spectra of (a) poly(MAA-co-TFA)/PVDF electrospun fiber, (b) TiO2–ZnS/ fluoropolymer fiber composites prepared by reactants TiZn2.

531.7 eV, 532.8 eV in the O1s spectrum, shown in Fig. 5b and c, and the peaks were also able to ascribe to the influence of carboxyl coordinated with nonbonding metal ion of semiconductor [19]. As a result, the semiconductor particles were able to immobilize tightly on the surface of fluoropolymer fibers. UV/Vis spectra show the photosensitive properties of TiO2/ZnS– fluoropolymer fiber composites. The poly(MAA-co-TFA)/PVDF electrospun fiber mats have no evident absorption above 250 nm wavenumbers (Fig. 6a). This reveals the poly(MAA-co-TFA)/PVDF electrospun fiber mats do not disturb the light absorption of semiconductor of TiO2/ZnS–fluoropolymer fiber composites during the photocatalytic process. The UV/Vis absorption spectrum of the TiO2–fluoropolymer fiber composites reflects that the absorption edge is about 382 nm, as shown in Fig. 6b. The UV/Vis absorption edge of TiO2–ZnS/fluoropolymer fiber composites have obviously shift to the long wavelength, as shown in Fig. 6c–f. It is due to the S of ZnS surface change the light absorption character of TiO2–ZnS, reduce the band gap, [20] and result in the improvement of the visible-light response ability of TiO2–ZnS/fluoropolymer fiber composites. When the reaction system have lower content zinc ion, the TiO2 crystals were compounded and mixed very well with ZnS through heterogeneous nucleation, and the TiO2–ZnS particles have strong compound effect, therefore the respectively absorption edge is about 473 nm and 450 nm, as shown in Fig. 6c and d. However, with the zinc ion content of reaction system increased, the ZnS agglomeration generation, and ZnS crystals were hard to decompose for TiO2 crystals combining, so the TiO2 crystals are not capped very well with ZnS crystals, therefore the compound effect reduces, the respectively absorption edge is about 402 nm and 390 nm, as shown in Fig. 6e and f. TGA curve of poly(MAA-co-TFA)/PVDF electrospun fiber shows several thermal decomposition stages, but TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2 does not show thermal decomposition stage until 450 °C, as shown in Fig. 7. This phenomenon may be due to that the low-molecular weight substances of poly(MAA-co-TFA)/PVDF electrospun fiber mats dissolved or fused connected under long-time hydrothermal condition, and the interaction between semiconductors particles and fluoropolymer fibers may also improve the thermal stability of TiO2–ZnS/fluoropolymer

1473

T. He et al. / Composites Science and Technology 70 (2010) 1469–1475

Relative Intensity (cps)

x10

6

1.5

1.0

a

O1s

Zn2p

Ti2p F1s C1s

0.5 S2p

1000

800

600

400

200

Binding Energy (eV)

C1s

O1s

c

Intensity (cps)

Intensity (cps)

b

292

290

288

286

284

282

280

534

532

Binding Energy (eV)

530

528

Binding Energy (eV)

Fig. 5. XPS spectrum of TiO2–ZnS/fluoropolymer fiber composites prepared by reactants TiZn2 (a) survage, (b) C1s, (c) O1s.

1.6

100

75

Weight (%)

Absorbance

1.2

0.8

d c e f b a

0.4

0.0 200

400

600

50

0 200

Wavelength nm

fiber composites. Semiconductor particles content of TiO2–ZnS/fluoropolymer fiber composites was measured though the weight loss after fluoropolymer electrospun fiber was fully decomposed at 700 °C, and the TiO2–ZnS content of TiO2–ZnS/fluoropolymer fiber composites calculated was 24.9%. The specific surface area of TiO2–ZnS of TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2 is considerably higher than that of Degussa P25 and poly(MAA-co-TFA)/PVDF electrospun fiber mats, but is lower than that of TiO2–ZnS powders, as shown in Table 2. 3.3. Photocatalytic degradation of methylene blue Photocatalysis of TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2, TiO2–ZnS powders, Degussa P25, fluoropolymer

a

25

800

Fig. 6. UV/VIS absorption spectra of (a) poly(MAA-co-TFA)/PVDF electrospun fiber mats, and the TiO2–ZnS/fluoropolymer fiber composites prepared by different reactants (b) TiZn0, (c) TiZn1, (d) TiZn2, (e) TiZn3, (f) TiZn4.

b

400

600 0

Temperature ( C) Fig. 7. Thermal gravity analytical of (a) poly(MAA-co-TFA)/PVDF electrospun fiber mats and (b) TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2.

Table 2 Specific surface area. Sample

SBET (m2 g

Degussa P25 TiO2–ZnS powders (MAA-co-TFA)/PVDF electrospun fiber mats TiO2–ZnS of TiO2–ZnS/fluoropolymer composites (TiZn2)

50.0 115.1 37.2 96.7

1

)

electrospun fiber mats and blank sample were performed for the methylene blue degradation under visible-light irradiation, as shown in Fig. 8. Near-complete degradation of methylene blue occurred in 120 min in the presence of TiO2–ZnS/fluoropolymer fiber composites, as shown in Fig. 8a. A slight change of the methylene

1474

T. He et al. / Composites Science and Technology 70 (2010) 1469–1475

100

e d c

C/C0(%)

75

50

25

b a

0 -15

0

40

80

120

Time (min) Fig. 8. Photocatalytic degradation of methylene blue by (a) TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2, (b) TiO2–ZnS powders, (c) Degussa P25, (d) (MAA-co-TFA)/PVDF electrospun fiber mats; (e) blank sample.

blue concentration was observed for the blank sample, as shown in Fig. 8e. The remaining methylene blue is 0.01 wt.% in the presence of TiO2–ZnS/fluoropolymer fiber composites, and it is 75.6 wt.% in the presence of Degussa P25 after 110 min visible-light irradiation, as shown in Fig. 8a and c. So the TiO2–ZnS/fluoropolymer fiber composites exhibited higher photocatalytic efficiency than that of TiO2 powder in the almost same TiO2 concentration (Table 3). The reason is that the specific surface area and visible-light respond ability of TiO2–ZnS/fluoropolymer fiber composites were higher than that of Degussa P25 (Table 2). The specific surface area of TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2 was lower of than that of TiO2–ZnS powder, as shown in Table 2, but the remaining methylene blue is 20.2 wt.% after 110 min visible-light irradiation in the presence of TiO2–ZnS powders. There may be adsorption–migration–photodegradation [21] exists in the photocatalysis reaction: methylene blue was first adsorbed onto the surface of fluoropolymer fibers because of its hydrophobicity, and

Table 3 Photocatalyst concentration in solution.

then migrated to semiconductor particles surface, finally was photocatalytic degraded by semiconductor particles, so deduce the TiO2–ZnS/fluoropolymer fiber composites possess higher photocatalytic efficiency than that of TiO2–ZnS powders for the degradation of methylene blue with the same concentration. The photocatalytic stability of TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2 evaluated by the degradation of methylene blue solution under 10 times of repeated visible-light irradiation for 120 min. The results reveal that the photocatalytic activity of TiO2–ZnS/fluoropolymer fiber composites changes indistinctively. The SEM image of TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2 after 10 times degradation of methylene blue solution shows that the semiconductor particles are tightly immobilized on the surface of fluoropolymer nanofibers after the degradation tests. As a conclusion, the TiO2–ZnS/fluoropolymer fiber composites possess high photocatalytic stability for the photodegradation of organic pollutants Fig. 9. 4. Conclusion The TiO2–ZnS composites with diameters from 15 nm to 1 lm were immobilize on the surface of fluoropolymer fiber under different reaction system, and the chemical interaction existed between TiO2–ZnS composites and fluoropolymer fibers. When the molar ratio of zinc ion and titanic ion in reaction system was 1:80, the TiO2– ZnS/fluoropolymer fiber composites possess good visible-light photocatalytic activity because of its strong visible-light response activity, quite high specific area and synergistic effect. The repeated photocatalysis tests show the TiO2–ZnS/fluoropolymer fiber composites possess good visible-light photocatalytic stability. Acknowledgments This work is supported by the National Natural Science Foundation of China (20776034), Doctoral Fund of Ministry of Education of China (20070359036). References

Sample

Photocatalyst (mg L

TiO2–ZnS/fluoropolymer fiber composites (TiZn2) TiO2–ZnS powders Degussa P25 (MAA-co-TFA)/PVDF electrospun fiber mats Blank

34.2 34.7 35.1 – –

1

)

Fig. 9. SEM image of TiO2–ZnS/fluoropolymer fiber composites prepared by TiZn2 after 10 times degradation of methylene blue solution under UV irradiation for 2.0 h each.

[1] Cao Y, Gao Z, Zhu J, Wang Q, Huang Y, Chiu C, et al. Impacts of halogen additions on mercury oxidation, in a slipstream selective catalyst reduction (SCR), reactor when burning sub-bituminous coal. Environ Sci Technol 2007;42:256–61. [2] Hamming LM, Qiao R, Messersmith PB, Catherine Brinson L. Effects of dispersion and interfacial modification on the macroscale properties of TiO2 polymer–matrix nanocomposites. Compos Sci Technol 2009;69:1880–6. [3] Tomonori N, Akira S, Hiroshi O. Optically excited near-surface phonons of TiO2 (110) observed by fourth-order coherent Raman spectroscopy. J Chem Phys 2009;131:084703–8. [4] Li D, Xia YN. Direct fabrication of composite and ceramic hollow nanofibers by electrospinning. Nano Lett 2004;4:933–8. [5] Jin M, Zhang XT, Nishimoto S, Liu ZY, Tryk DA, Emeline AV, et al. Lightstimulated composition conversion in TiO2 -based nanofibers. J Phys Chem C 2007;111:658–65. [6] Zhao Y, Zhang X, Zhai J, He J, Jiang L, Liu Z, et al. Enhanced photocatalytic activity of hierarchically micro-/nano-porous TiO2 films. Appl Catal B 2008;83:24–9. [7] KKC H, Kalinka G, Tran M. Fluorinated carbon fibres and their suitability as reinforcement for fluoropolymers. Compos Sci Technol 2007;67:2699–706. [8] Huang Z-M, Zhang YZ, Kotaki M, Ramakrishna S. A review on polymer nanofibers by electrospinning and their applications in nanocomposites. Compos Sci Technol 2003;63:2223–53. [9] Huang J, Wang D, Hou H, You T. Electrospun palladium nanoparticle-loaded carbon nanofibers and their electrocatalytic activities towards hydrogen peroxide and NADH. Adv Funct Mater 2008;18:441. [10] Stengl V, Bakardjieva S, Murafa N, Houskova V, Lang K. Visible-light photocatalytic activity of TiO2/ZnS nanocomposites prepared by homogeneous hydrolysis. Microporous Mesoporous Mater 2008;110:370–8. [11] Zhou Z, He D, Xu W, Ren F, Qian Y. Preparing ZnS nanoparticles on the surface of carboxylic poly(vinyl alcohol) nanofibers. Mater Lett 2007;61:4500–3. [12] Li Zhang LY. Hydrothermal growth of ZnS microspheres and their temperature-dependent luminescence properties. Cryst Res Technol 2008;43:1022–5.

T. He et al. / Composites Science and Technology 70 (2010) 1469–1475 [13] Soler-Illia G, Jobbagy M, Candal RJ, Regazzoni AE. Synthesis of metal oxide particles from aqueous media: The homogeneous alkalinization method. J Dispersion Sci Technol 1998;19:207–28. [14] Wu J, Schultz JM, Yeh F, Hsiao BS, Chu B. In Situ simultaneous synchrotron small- and wide-angle X-ray scattering measurement of poly(vinylidene fluoride) fibers under deformation. Macromolecules 2000;33:1765–77. [15] Drew C, Wang XY, Bruno FF, Samuelson LA, Kumar J. Electrospun polymer nanofibers coated with metal oxides by liquid phase deposition. Compos Interfaces 2005;11:711–24. [16] Graziola F, Girardi F, Bauer M, Di Maggio R, Rovezzi M, Bertagnolli H, et al. UVphotopolymerisation of poly(methyl methacrylate)-based inorganic–organic hybrid coatings and bulk samples reinforced with methacrylate-modified zirconium oxocluster. Polymer 2008;49:4332–43.

1475

[17] Willneff EA, Braun S, Rosenthal D, Bluhm H, Havecker M, Kleimenov E, et al. Dynamic electronic structure of a Au/TiO2 catalyst under reaction conditions. J Am Chem Soc 2006;128:12052–3. [18] Woan K, Pyrgiotakis G, Sigmund W. Photocatalytic carbon-nanotube-TiO2 composites. Adv Mater 2009;21:2233–9. [19] Shanmugasundaram S, Horst K. Daylight photocatalysis by carbon-modified titanium dioxide. Angew Chem Int Ed 2003;42:4908–11. [20] Tao Q, Zhang Y, Zhang X, Yuan P, He H. Synthesis and characterization of layered double hydroxides with a high aspect ratio. J Solid State Chem 2006;179:708–15. [21] Matos J, Laine J, Herrmann JM. Effect of the type of activated carbons on the photocatalytic degradation of aqueous organic pollutants by UV-irradiated titania. J Catal 2001;200:10–20.