Fabrication Of TiO₂ And Silicon-doped TiO₂ Nanostructured Film Electrodes And Their Photoelectrocatalytic Performance

Photocatalytic oxidation used TiO₂, one of the most attractive techniques for environmental pollution control, has been widely investigated. The immobilized TiO₂ nanofilm could solve the separation and recovery problems of powdery photocatalyst, but decreasing the photocatalytic (PC) activity due to its lower surface area, which hampers its practical application. In the present work, anatase nanoparticles film and nanowires film were prepared in order to improve the PC activity of TiO₂ nanofilm. The shape-tunable properties of synthesizable nanomaterials and their PC capabilities were investigated. The silicon modification could improve the ultraviolet PC activity of TiO₂ nanotube arrays film. Meanwhile, photoelectrocatalytic (PEC) oxidation can prevent the simple combination of photogenerated electrons and holes, consequently improving the PC efficiency of TiO₂. In this dissertation, some works were carried out as follows:(1) The nanostructured anatase film (NAF), consisted of nanoparticles or nanowires, was fabricated directly on Ti substrate by a two-step hydrothermal approach. At lower hydrothermal temperature, a uniform film of anatase nanoparticles mainly consisted of nanoscale cubes and rhombohedra was fabricated. The average size of these nanoparticles was smaller than 15 nm. At higher hydrothermal temperature, anatase nanowires film which consisted of combination of monodispersed anatase nanocrystals and aggregates of anatase nanocrystals formed on Ti substrate. X-ray diffraction (XRD) analysis indicated that both NAFs possessed higher anatase crystallinity. The distinguished surface photovoltage responses and photocurrent densities of NAFs suggested that they had promising photoelectrochemical ability. The kinetic constants of PEC degradation towards phenol under UV light irradiation with NAF-nanoparticles and NAF-nanowires were 2.2 and 3.4 times as great as the values with CTF, respectively. A significant PEC synergetic effect between the photocatalytic and electrochemical processes was also observed.(2) The Si-doped TiO₂ nanofilm on Ti substrate was successfully prepared by chemical vapor deposition (CVD) with liquid injection. This method can control the Si-doping amount well by adjusting the precursor solution and obtain the rapid deposition rate of film. The average deposition rate of film prepared by this process was at least 10 times higher than that of TiO₂ film by other CVD processes. The analysis revealed that the introduced silicon might be incorporated into titania matrix and formed Si-O-Ti bonds. This incorporation helped to increase the thermal stability of titania, which was in favor of obtaining smaller anatase crystallites, higher crystallinity and enhanced UV absorption at high calcination temperature. The Si-doped sample with 5 at.% of silicon exhibited the best photoelectrochemical property, and its kinetic constants towards phenol degradation in PC and PEC processes under UV light irradiation were 1.3 and 1.8 times as great as the values for the undoped TiO₂ nanofilm.(3) The Si-doped titania nanotube arrays were fabricated by anodization, followed by CVD treatment. The obtained nanotube arrays show highly ordered and vertically oriented morphology, and the average length was about 1μm. Analysis by X-ray photoelectron spectroscopy (XPS) indicated that the introduced silicon might be incorporated into titania matrix and formed Si-O-Ti bonds. This incorporation helped to increase the thermal stability of titania, which suppressed the phase transformation of anatase and also inhibited the growth of anatase crystallite at high temperature. The Si-doped TiO₂ nanotube arrays showed an enhanced photoresponse in UV region and its absorption edge shifted 13 run to a higher energy. The surface of Si-doped sample showed a super-hydrophilic behavior under UV illumination. The Si-doped TiO₂ showed better PEC capability, its degradation rate for pentachlorophenol (PCP) under UV irradiation was 84.8% higher than that of undoped electrode. In addition, the Si-doped TiO₂ nanotube arrays with different Si-doping amounts were also fabricated by electrochemical anodization. This method provides a one-step way to implement the formation of nanotubes and Si-doping, which simplifies the preparation process. The results indicated the Si-doped nanotubes were highly ordered and vertically oriented on substrate. The introduced silicon might be incorporated into TiO₂ matrix and formed Si-O-Ti bonds, which was significant to improve thermal stability of TiO₂. Silicon doping facilitated in obtaining higher anatase crystallinity and small-sized anatase crystallite under high calcination temperature, and also enhanced absorption response in UV region. All the Si-doped electrodes showed the improved photoelectrochemical ability compared to the undoped one under UV illumination. The Si-doped sample with 4.2 at.% of silicon exhibited the best photoelectrochemical response and PEC degradation efficiency for PCP.The above results illuminated that the TiO₂ nanostructured films with unique architecture and modification of TiO₂ nanofilms with silicon can effectively enhance PC activity of TiO₂. The effects of morphologies of nanostructured films and silicon-doping amount on PC ability were also investigated, which was hoped to help optimize the PC capability of TiO₂ and develop TiO₂ photocatalyst in environmental pollution controlling.