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In Situ Growth of ZnO Nanocrystals from Solid Electrospun Nanofiber Matrixes Youliang Hong,*,† Dongmei Li,† Jian Zheng,‡ and Guangtian Zou† State Key Laboratory of Superhard Materials, Jilin UniVersity, Changchun 130012, PR China, and Beijing Centre for Physical and Chemical Analysis, Beijing 100027, PR China ReceiVed March 5, 2006. In Final Form: June 7, 2006 Porous fiber membranes consisting of 1D assemblies of ZnO nanocrystal-supported poly(vinyl alcohol) (PVA) nanofibers are described. These hybrid nanofiber membranes were assembled by first electrospinning a ZnO precursorcontaining PVA aqueous solution. Subsequently, the electrospun composite nanofibers were submerged in a basic ethanol solution. As a result, ZnO precursors in solid PVA matrixes were hydrolyzed to generate ZnO crystals residing on the fiber surfaces. Photoluminescence spectroscopy analysis demonstrated the as-hydrolyzed fiber membranes possess white luminescence. Furthermore, the ZnO-encapsulated PVA nanofibers were prepared by directly electrospinning a ZnO nanocrystal-containing PVA solution as the contrast of the as-hydrolyzed hybrid nanofibers. The surface photovoltage spectroscopy (SPS) confirmed that the as-hydrolyzed hybrid fiber membranes had a strong SPS response, but the directly spun fiber membranes did not have any SPS response. This can be attributed to the favorable structure of the hydrolyzed hybrid nanofibers, that is, the surface residence of ZnO permits ZnO crystals to make direct contact with ITO electrodes to transfer the photogenerated electron originating from ZnO to ITO electrodes. By contrast, the transfer of the photogenerated electron is limited by PVA matrixes in the directly spun fiber system.
Introduction Electrospinning, a top-down nanomanufacturing method, offers a quick and facile process to create high-surface-area polymer fibers compared to those produced by most bottom-up methods.1-6 Besides the preparation of pure polymer fibers, electrospinning has also been used to synthesize from polymer solution containing inorganic species.7 The purpose in using electrospinning to prepare the inorganic/organic composite nanofibers is to synthesize inorganic oxide nanofibers, as can be seen from Figure 1, route * To whom correspondence should be addressed. E-mail: hong_yl@ email.jlu.edu.cn. Tel: +86-4315168340. Fax: +86-4315166164. † Jilin University. ‡ Beijing Centre for Physical and Chemical Analysis. (1) (a) Doshi, J.; Reneker, D. H. J. Electrost. 1995, 35, 151. (b) Reneker, D. H.; Chun, I. Nanotechnology 1996, 7, 216. (c) Koombhongse, S.; Liu, W.; Reneker, D. H. J. Polym. Sci., Part B: Polym. Phys. 2001, 39, 2598. (d) Reneker, D. H.; Yarin, A. L.; Fong, H.; Koombhongse, S. J. Appl. Phys. 2000, 87, 4531. (e) Yarin, A. L.; Koombhongse, S.; Reneker, D. H. J. Appl. Phys. 2001, 89, 3018. (f) Yarin, A. L.; Koombhongse, S.; Reneker, D. H. J. Appl. Phys. 2001, 90, 4836. (g) Reneker, D. H.; Kataphinan, W.; Theron, A.; Zussman, E.; Yarin, A. L. Polymer 2002, 43, 6785. (2) (a) Hohman M. M.; Shin, Y. M.; Rutledge, G. C.; Brenner, M. P. Phys. Fluids 2001, 13, 2201. (b) Hohman M. M.; Shin, Y. M.; Rutledge, G. C.; Brenner, M. P. Phys. Fluids 2001, 13, 2221. (c) Shin, Y. M.; Hohman, M. M.; Brenner, M. P.; Rutledge, G. C. Appl. Phys. Lett. 2001, 78, 1149. (d) Shin, Y. M.; Hohman, M. M.; Brenner, M. P.; Rutledge, G. C. Polymer 2001, 42, 9955. (e) Fridrikh, S. V.; Yu, J. H.; Brenner, M. P.; Rutledge, G. C. Phys. ReV. Lett. 2003, 90, 144502. (3) (a) Theron, A.; Zussman, E.; Yarin, A. L. Nanotechnology 2001, 12, 384. (b) Zussman, E.; Yarin, A. L.; Weihs, D. Exp. Fluids 2002, 33, 315. (c) Zussman, E.; Rittel, D.; Yarin, A. L. Appl. Phys. Lett. 2003, 82, 3958. (4) (a) Bognitzki, M.; Czado, W.; Frese, T.; Schaper, A.; Hellwig, M.; Steinhart, M.; Greiner, A.; Wendorff, J. H. AdV. Mater. 2001, 13, 70. (b) Dersch, R.; Liu, T.; Schaper, A. K.; Greiner, A.; Wendorff, J. H. J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 545. (5) Li, D.; Xia, Y. AdV. Mater. 2004, 16, 1151. (6) Huang, Z. M.; Zhang, Y. Z.; Kotakic, M.; Ramakrishna, S. Compos. Sci. Technol. 2003, 63, 2223. (7) (a) Dai, H.; Gong, J.; Kim, H.; Lee, D. Nanotechnology 2002, 13, 674. (b) Li, D.; Y. Xia, Y. Nano Lett. 2003, 3, 555. (c) Li, D.; Wang, Y.; Xia, Y. Nano Lett. 2003, 3, 1167. (d) Li, D.; Herricks, T.; Xia, Y. Appl. Phys. Lett. 2003, 83, 4586. (e) Shao, C.; Kim, H. Y.; Gong, J.; Ding, B.; Lee, D. R.; Park, S. L. Mater. Lett. 2003, 57, 1579. (f) Yang, X.; Shao, C.; Guan, H.; Li, X.; Gong, J. Inorg. Chem. Commun. 2004, 7, 176. (g) Hong, Y. L.; Li, D. M.; Zheng, J.; Zou, G. T. Nanotechnology 2006, 17, 1986. (h) Wang, Y.; Santiago-Avile´s, J. J. Nanotechnology 2004, 15, 32. (i) Viswanathamurthi, P.; Bhattarai, N.; Kim, H. Y.; Lee, D. R. Nanotechnology 2004, 15, 320.
Figure 1. Illustration of two synthetic routes to prepare different products stemming from the same inorganic/organic composite nanofibers.
1. In this instance, the component polymer inside the composite fibers generally needs to be removed under high temperature. Although perfect polycrystalline inorganic oxide nanofibers such as TiO2, ZnO, and NiFe2O4 can easily be synthesized in this manner, the removal of the polymer also reduces the elasticity and mechanical strength of composite nanofibers. Improved properties may result if the inorganic precursors inside the composite nanofibers can be converted into inorganic oxides while the component polymer inside the composite nanofibers can be retained. Because of wide applications in many areas such as gas sensors, antimicrobials, and optical devices,8 ZnO has been attracting attention in both fundamental and practical studies, and a variety of micro/nanoscale building blocks (crystals, rods, tubes, etc.) created using different methods have also been reported in recent years.9Very little attention has been directed toward the incorporation of ZnO nanostructures in polymer systems to form functional micro/nanostructures.10 Methods of assembling inorganic nanoparticles into polymer matrixes include a mixture of preformed nanoparticles and polymers,11 plasma deposition,12 and in situ growth.13 There is new interest in the latter mode of (8) (a) Gruber, D.; Kraus, F.; Mu¨ller, J. Sens. Actuators, B 2003, 92, 81. (b) Yamamoto, O. Int. J. Inorg. Mater. 2001, 3, 643. (c) Pang, Z.; Dai, Z.; Wang, Z. Science 2001, 291, 1947. (9) (a) Abdullah, M.; Morimoto, T.; Okuyama, K. AdV. Funct. Mater. 2003, 13, 800. (b) Huang, M. H.; Mao, S.; Feick, H.; Yan, H. Q.; Wu, Y. Y.; Kind, H.; Weber, E.; Russo, R.; Yang, P. D. Science 2001, 292, 1897. (c) Zhang, X.; Xie, S.; Jiang, Z.; Zhang, X.; Tian, Z.; Xie, Z.; Huang, R.; Zheng, L. J. Phys. Chem. B 2003, 107, 10114.
10.1021/la0605992 CCC: $33.50 © 2006 American Chemical Society Published on Web 07/13/2006
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synthesis inside solid matrixes.14 However, the in situ synthesis of ZnO nanocrystals in solid polymer matrixes still remains a highly sophisticated challenge. The present study aims to address this challenge by means of electrospinning followed by an in situ hydrolysis process (Figure 1, route 2). Photoluminescence (PL) and surface photovoltage spectroscopy (SPS) analysis are further employed to evaluate the luminescence and optoelectronic properties of the ashydrolyzed fiber membranes. It is worth noting that another kind of ZnO crystals/PVA hybrid nanofiber was reported recently by directly electrospinning a ZnO-containing PVA aqueous solution.10b However, these directly spun hybrid fibers are different in structure and morphology from those that we produce, the in situ-hydrolyzed hybrid fibers. In our hybrid fibers, ZnO crystals reside on the fiber surface, whereas in directly spun hybrid fibers crystals are encapsulated in the fiber interior. The structural and morphological differences between two kinds of ZnO/PVA hybrid fibers trigger our motivation in comparing them by using the SPS technique. Experimental results confirmed that the as-hydrolyzed hybrid fiber membranes had a strong SPS response but the directly spun fibers did not have any SPS response. Experimental Section Preparation of the PVA Nanofibers with Surface-Resident ZnO Nanocrystals. In a typical experiment, 1.6 g of PVA powder (MW 86 000) was added to 20 mL of 95 °C deionized water with magnetic stirring. After PVA was dissolved completely (the aqueous solution was completely clear), the solution was cooled to 40 °C. Zinc acetate (0.4 or 2 g) and acetic acid (used to adjust the solution pH to 6) were then added to the PVA aqueous solution with magnetic stirring. Twenty minutes later, the ZnO precursor-containing PVA aqueous solution was transferred to a syringe for electrospinning. The syringe needle was connected to a high-voltage supply (ES30P5W, Gamma High Voltage Research Inc., Ormond Beach, FL) that is capable of generating dc voltages up to 30 kV. The distance between the tip of the needle and the aluminum foil was fixed at 20 cm. At room temperature and in air, a potential of 12 kV was applied for electrospinning. The feed rate of the solution was kept at 1.0-1.5 mL/h by a syringe pump. The fibers were collected using different collectors. Samples for SEM studies were collected on aluminum foil, and samples for immersion in water were electrospun onto a stainless steel web. After being dried in air for 24 h, the as-spun composite fibers loaded on a stainless steel web were immersed in a basic ethanol solution whose pH was held at 10-12 for 24 h (the basic reagent can be ammonia, NaOH, or LiOH). Before being analyzed, these samples were dried again for 24 h in a desiccator. Preparation of the ZnO-Encapsulated PVA Nanofibers. To compare with the as-hydrolyzed fibers, the ZnO-encapsulated PVA nanofibers were electrospun. First, ZnO nanocrystals were prepared according to the process described by Spanhel et al.15 The synthesized ZnO colloid solution was diluted with the desired volume of deionized (10) (a) Li, L.; Beniash, E.; Zubarev, E. R.; Xiang, W.; Rabatic, B. M.; Zhang, G.; Stupp, S. I. Nat. Mater. 2003, 2, 689. (b) Sui, X. M.; Shao, C. L.; Liu, Y. C. Appl. Phys. Lett. 2005, 87, 113115. (11) (a) Bashouti, M.; Salalha, W.; Brumer, M.; Zussman, E.; Lifshitz, E. Chem. Phys. Chem. 2006, 7, 102. (b) Dror, Y.; Salalha, W.; Khalfin, R. L.; Cohen, Y.; Yarin, A. L.; Zussman, E. Langmuir 2003, 19, 7012. (c) Salalha, W.; Dror, Y.; Khalfin, R. L.; Cohen, Y.; Yarin, A. L.; Zussman, E. Langmuir 2004, 20, 9852. (d) Kedem, S.; Schmidt, J.; Paz, Y.; Cohen, Y. Langmuir 2005, 21, 5600. (e) Tan, S. T.; Wendorff, J. H.; Pietzonka, C.; Jia, Z. H.; Wang, G. Q.; Chem. Phys. Chem. 2005, 6, 1461. (f) Schlecht, S.; Tan, S.; Yosef, M.; Dersch, R.; Wendorff, J. H. Chem. Mater. 2005, 17, 809. (g) Wang, M.; Singh, H.; Hatton, T. A.; Rutledge, G. C. Polymer 2004, 45, 5505. (12) Heilmann, A. Polymer Films with Embedded Metal Nanoparticles; Springer-Verlag: New York, 2002. (13) Korchev, A. S.; Bozack, M. J.; Slaten, B. L.; Mills, G. J. Am. Chem. Soc. 2004, 126, 10. (14) (a) Sone, E. D.; Zubrarev, E. R.; Stupp, S. I. Angew. Chem., Int. Ed. 2002, 41, 1706. (b) Majumdar, G.; Gogoi, S. K.; Paul, A.; Chattopadhyay, A. Langmuir 2006, 22, 3439.
Hong et al. water, and then ethanol was removed rapidly under reduced pressure by a rotary evaporator. (After the ZnO colloid solution had undergone a complete solvent substitution, the mean size of ZnO nanocrystals grew from ca. 5 to ca. 20 nm as determined by TEM.) Last, a 1 M ZnO aqueous solution was obtained. The resulting ZnO aqueous solution (4 mL) was subsequently incorporated into 16 mL of a 10 wt % PVA aqueous solution with stirring. Before electrospinning, the ZnO/PVA solution was placed in an ultrasonic bath for 1 h using a digitally controlled ultrasonic rinser (KQ-250kD, power 250 W, frequency 40 kHz) to disperse enough ZnO nanocrystals. The parameters for the electrospinning procedure were the same as those of the above-mentioned procedure. Characterization. SEM images of samples were obtained using an environmental scanning electron microscope (model XL 30 ESEM FEG from Micro FEI Philips). A transmission electron microscope (TEM, Hitachi S-570) was used to collect TEM images of samples. Before being characterized, these samples were transferred onto Formvar-coated copper grids. The powder X-ray diffraction pattern (XRD, Siemens D-5005, Cu KR radiation) was used to measure the crystallinity of the samples, and the photoluminescence (PL) spectrum was recorded by a Renishaw-1000 confocal Raman microscope using a He-Cd laser as the excitation light source and keeping the laser power at 0.7 mW to avoid sample degradation. Before investigation, the sample (10 × 10 mm2) was mounted on a microscope slide. SPS Analysis. To investigate the surface character of the ashydrolyzed fibers and compare with the ZnO-encapsulated PVA fiber nonwovens, SPS measurements were carried out with a solid junction photovoltaic cell (ITO/sample/ITO) using a light sourcemonochromator-lock-in detection technique. The principle and setup diagrams of SPS measurements were described in detail elsewhere.16a In brief, the generation of photovoltage arises from the creation of electron-hole pairs, followed by the separation under a built-in electric field (the space-charge layer). The difference between the surface potential barrier in the light and that in the dark is the SPS signal.16 Monochromatic light was obtained by passing light from the 500 W xenon lamp through a double-prism monochromator (Hilger and Watt, D300). A lock-in amplifier (SR830-DSP) synchronized with a light chopper was employed to amplify the photovoltage. The spectra were normalized to unity at their maxima, and the feature peaks of the xenon lamp were deducted by a computer. The measurement was performed at room temperature.
Results and Discussion The hybrid ZnO precursors/PVA nanofibers were produced rapidly by electrospinning an 8 wt % PVA aqueous solution containing zinc acetate and by precisely controlling the different electrospinning parameters (e.g., distance between anode and cathode, diameter of the syringe tip, applied voltage, etc.). The purpose of adding acetic acid (to keep the solution pH at 6) is to avoid the possible weak hydrolysis of CH3COO- to form OH-, which was likely to yield Zn2+ in the formation of Zn(OH)2.17
CH3COO- + H2O T CH3COOH + OHZn2+ + OH- T Zn(OH)2 Figure 2a shows that the mean diameter of the hybrid nanofibers is 300 ( 60 nm, and a TEM image (Figure 2b) further confirms that ZnO precursors in the hybrid fiber are stable without the emergence of inorganic particles on the fiber surface and in the fiber interior. An X-ray diffraction (XRD) pattern was further (15) Spanhel, L.; Anderson, M. A. J. Am. Chem. Soc. 1991, 113, 2826. (16) (a) Wang, D.; Zhang, J.; Shi, T.; Wang, B.; Cao, X.; Li, T. J. Photochem. Photobiol., A 1993, 93, 21. (b) Lin, Y.; Wang, D.; Zhao, Q.; Yang, M.; Zhang, Q. J. Phys. Chem. B 2004, 108, 3202. (17) (a) Li, W. J.; Shi, E. W.; Zhong, W. Z.; Yin, Z. W. J. Cryst. Growth 1999, 203, 186. (b) Zhang, J.; Sun, L.; Yin, J.; Su, H.; Liao, C.; Yan, C. Chem. Mater. 2002, 14, 4172. (c) Xu, H. Y.; Wang, H.; Zhang, Y. C.; He, W. L.; Zhu, M. K.; Wang, B.; Yan, H. Ceram. Int. 2004, 30, 93.
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can see from Figure 3b that the XRD pattern presents different peaks besides the PVA peak at 20°. The peaks in the range from 30 to 70° indicate that the formed crystals have the typical wurtzite structure of ZnO (JCPDS, 80-0075), and no peaks denoting Zn(OH)n or Zn(NH3)n emerge. The XRD results confirm that ZnO precursors have been converted completely into ZnO. According to these results, the formation of ZnO nanocrystals from the composite nanofibers can be described by a chemical formula as follows. Figure 2. SEM (a) and TEM (b) images of ZnO precursor/PVA hybrid fibers. The weight ratio of zinc acetate to PVA is 1/8.
OH-
Zn precursors/PVA nanofibers 98 ZnO/PVA nanofibers
employed to analyze the ZnO precursors/PVA hybrid nanofibers, and the resulting pattern is shown in Figure 3a. One can see that this curve indicates only a broad peak at 20°. The peak can be attributed to the crystallinity of PVA, which is a semicrystalline polymer.18 This XRD pattern demonstrated that ZnO precursors in the as-synthesized form were amorphous. Various routes to the synthesis of ZnO crystals by wet chemical methods such as the sol-gel technique, pyrolysis, hydrothermal methods, and so forth15,17,19 have been introduced over the past few years. The fabrication of ZnO via the solution route is based on forming Zn precursors (e.g., Zn(OH)42- and Zn(NH3)42+) under basic conditions as the growth unit to incorporate into ZnO crystallites directly.17 In the same way, the wet chemical method is also attempted by us to treat the as-spun composite nanofibers. In practice, the composite fiber membranes were introduced into a basic ethanol solution (the basic reagent can be ammonia, NaOH, or LiOH) of pH 10 at room temperature for 24 h. Interestingly, the resulting SEM images (Figure 4a and b) show that ZnO nanocrystals were formed and resided on the fiber surface. These images clearly indicate that higher concentrations of ZnO precursors in hybrid fibers resulted in the formation of nanocrystals on the fiber surface with a higher density and a larger diameter. Further investigation using TEM reveals that low concentrations of ZnO precursors in the fiber matrixes resulted in the formation of crystals with different diameters from ca. 5 to 30 nm on the fiber surface (Figure 4c and e) and an increase in ZnO precursor concentration tended to form crystals with a broader size distribution (from ca. 10 to 200 nm) in the fiber exterior (Figure 4d and f). Furthermore, one
Experimental results demonstrate that the pH and temperature of the immersion solvent are important. The immersion solvent with high pH (g13) or temperature (g60 °C) resulted easily in the growth units of ZnO failing to reside and incorporate on the fiber surface (Supporting Information). This result suggests that ZnO nanocrystals will reside on the fiber surface if a relatively low pH and temperature are used, which in essence requires a low hydrolysis velocity of ZnO precursors. During the synthesis of ZnO nanocrystals by wet chemical methods, zinc reactant molecules are generally dissolved in a solution, and during the whole reaction process Zn2+ or its growth unit can move freely in solution to incorporate into nanocrystals. However, our ZnO precursors are in a fixed state (i.e., these precursors are restricted inside solid PVA fiber matrixes). This means that the kinetics of nucleation and accretion and the forming mechanism of ZnO nanocrystals are completely different from the above-mentioned solution routes. From the morphology of the nanocrystals and the experimental results, we speculate that the interdiffusion of small molecules in the composite nanofibers may play a key role. After the ZnO precursor-containing PVA nanofibers were immersed in a solution containing a hydrolysis reagent, reactant molecules could meet ZnO precursors in a fiber surface layer and were even likely to permeate gradually into the fiber interior along pores. Also, free volume existed in the fiber matrixes20 to meet ZnO precursors. As a result, ZnO precursors were hydrolyzed and diffused inversely along the pores and free volume on the fiber surface to concentrate into ZnO nanocrystals. A detailed investigation of the growth mode is currently under study. PL of the as-hydrolyzed sample shown in Figure 5 was measured using a He-Cd laser (λex ) 325 nm) as the excitation source. Interestingly, three peaks, the peak at 357 nm can be attributed to the emission of ZnO and PVA, the peak at 440 nm is of PVA, and the peak at 550 nm is of ZnO,10,21 covering the UV to visible area. As a consequence, white luminescence is observed. In addition to the optical function, optoelectronic properties of ZnO-loaded fiber membranes were investigated further by employing SPS, which is a technique used to study charge transfer in photostimulated surface interactions and can demonstrate the optoelectronic properties of semiconductors under the effect of an external electric field.16 Figure 6a shows a strong SPS response at 370 nm. The response can be attributed to the electronic bandband transfer.16 Furthermore, the SPS result also suggests that our products in which crystals reside on the fiber surface have more structural advantages than products in which crystals are encapsulated in polymer matrixes. For example, the ZnOencapsulated fiber membrane, which was synthesized by electrospinning a ZnO nanocrystal-containing PVA aqueous solution and was used as a contrast for our products (as can be seen from
(18) Hong, Y.; Shang, T.; Li, Y.; Wang, L.; Wang, C.; Chen, X.; Jing, X. J. Membr. Sci. 2006, 276, 1. (19) (a) Milosevic, O.; Uskokovic, D. Mater. Sci. Eng., A 1993, 168, 249. (b) Chen, D. R.; Jiao, X. L.; Cheng, G. Solid State Commun. 2000, 113, 363.
(20) Yao, L.; Haas, T. W.; Guiseppi-Elie, A.; Bowlin, G. L.; Simpson, D. G.; Wnek, G. E. Chem. Mater. 2003, 15, 1860. (21) Shan, W.; Walukiewicz, W.; Ager, J. W., III; Yu, K. M.; Yuan, H. B.; Xin, H. P.; Cantwell, G.; Song, J. J. Appl. Phys. Lett. 2005, 86, 191911.
Figure 3. Powder X-ray diffraction pattern of ZnO precursors/ PVA hybrid fiber membranes (the weight ratio of zinc acetate to PVA matrixes is 0.2/8) before (a) and after (b) immersion in a basic ethanol solution.
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Figure 4. (a and b) SEM images of the ZnO/PVA composite fibers. Before these composite fibers were immersed in a basic ethanol solution for 24 h, the weight ratio of zinc acetate to PVA matrixes was 0.2/8 (a) and 1/8 (b). (c and d) Corresponding TEM images of a and b, respectively. (e, f) Histogram showing the size distribution of ZnO nanocrystals. (e and f) Bar graphs of samples a and b, respectively. The size distribution was obtained from ∼100 nanocrystals.
Figure 5. PL spectrum of the membrane shown in Figure 4a (λex ) 325 nm).
Figure 6. SPS of (a) the membrane shown in Figure 4a and (b) a ZnO-encapsulated PVA membrane. The inset is the TEM image of a ZnO-encapsulated PVA fiber.
the inset shown in Figure 6, ZnO crystals are encapsulated successfully into PVA matrixes), displays (Figure 6b) no SPS response at 370 nm. The cause of no SPS response in the ZnOencapsulated fibers is that the photogenerated electric transfer originating from ZnO crystals is prohibited as a result of the encapsulation of PVA matrixes. By contrast, the capability of optoelectronic transfer possessed by an as-hydrolyzed membrane results from the residence of ZnO on the fiber surface, which allows ZnO to make direct contact with the ITO electrodes.
white luminescence. SPS demonstrates that the ZnO surfaceresiding fiber membranes possess optoelectronic properties due to their favorable structure (i.e., the optoelectronic properties of ZnO are not occluded by PVA matrixes). The present ZnOloaded PVA porous fiber membranes could be useful for a wide range of optical, antibacterial, and gas sensor membranes.
Conclusions This is the first report of in situ fabrication in a solid polymer matrix by a wet chemical method leading to the assembly of ZnO nanocrystals with 1D polymer nanoarchitectures. The formation of nanofibers with surface-resident ZnO nanoparticles is likely due to the interdiffusion of molecules in polymer fiber matrixes during hydrolysis. The combination of ZnO nanocrystals with the PVA fiber membranes endows novel membranes with
Acknowledgment. We are grateful to Professor Y. Xia and Dr. D. Li from the University of Washington and Professor D. H. Reneker from the University of Akron for their help in improving this article. We acknowledge financial support from the Young Teacher Foundation of Jilin University (no. 419080102460). Supporting Information Available: SEM image of the ZnO precursors/PVA hybrid fibers undergoing a high temperature and pH immersion. This material is available free of charge via the Internet at http://pubs.acs.org. LA0605992
