Novel Strategies for the Preparation of TiO 2 Nanofibers
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Novel Strategies for the Preparation of TiO2 Nanofibers Kenneth J. Balkus, Jr., Chunrong Xiong and Minedys Macias-Guzman Department of Chemistry and the UTD NanoTech Institute, University of Texas at Dallas Richardson, TX 75083-0688, U.S.A. ABSTRACT The various polymorphs of titanium oxide (TiO2) are probably the most widely studied materials for photovoltaic applications. It is well known that composition and particles size can have a profound effect on photoactivity. It is thought that high surface to volume nanostructures such as nanofibers and nanorods may possess the optimal properties. We have developed technology for the preparation of TiO2 nanofibers in a variety of forms including core shell structures, papers and films. The formation of mesoporous TiO2 fibers as spider webs and papers has been achieved by electrostatic deposition. The mesoporous fibers and other forms such as shaped particles and films have been employed as templates to grow TiO2 nanofibers in various configurations. The proposed research below will address the synthesis and characterization of the TiO2 fibers developed by these techniques INTRODUCTION Titanium dioxide (TiO2) is widely studied for its potential application in high performance photovoltaics. Dimensionality becomes a crucial factor in determining the properties of nanomaterials including surface area. Therefore, efforts have been made to decrease the particle size of porous or dense forms of titania [1-4]. In addition to nanoparticles, there may be advantages to preparing TiO2 as high surface area fibers. The probability of electron-hole recombination at surface trap sites increases with nanoparticles. In contrast, nanofibers or nanorods the electron-hole recombination may be reduced because of improved delocalization of carriers. TiO2 nanorods have been prepared by controlled growth using an organic capping technique [5]. Well aligned rutile and anatase TiO2 nanorods have also been prepared by MOCVD [6]. Titania nanofibers have also been electrospun from titanium isopropoxide mixed with acetic acid and high molecular weight polyvinylpyrrolidone (PVP) to form amorphous titania nanofibers [7]. Amorphous titania films with micrometer sized pores has also been formed by electrostatic sol-spray deposition (ESSD) using titanium isopropoxide [8]. Although there has been progress in fabricating dense TiO2 in various configurations there has been little reported regarding the morphogenesis of mesoporous TiO2 molecular sieves. Mesoporous TiO2 has been prepared as bulk powders and films [9-16]. For example, Grätzel and co-workers achieved 7% efficiency by employing a ruthenium dye complex adsorbed onto a mesoporous TiO2 nanocrystalline film [17]. Subsequent studies have shown that several characteristics of the TiO2 film including the size and degree of crystallinity, affect the overall efficiency of the cell [18-19]. Yanagida and co-workers concluded that the diffusion coefficient of electrons increased with an increase in TiO2 particles size while electron recombination lif
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