Study On The Fabrication Of Metal-Doped TiO₂Nanotubes And Their Photoelectrocatalytic Reductive Dechlorination Performance

With the development of the global economy, pentachlorophenol (PCP) is widely used in wood preservatives, anti-rust agents, herbicides, fungicides and the paper industry. As a representative of the typical persistent organic pollutants (POPs), pentachlorophenol has three induced effects of carcinogenicity, teratogenicity and mutagenicity, respectively. It will not purify in natural environment and is difficult to degrade by biochemical methods because of its chemical stability, and thus become the hotspot in the field of environmental science between international institutions and developed countries.The researches of photocatalytic degradation PCP by nano-semiconductor catalysts have been reported elsewhere. Highly ordered TiO2nanotube arrays fabricated by anodization have attracted significant interest due to their unique advantages including highly-oriented array structure, larger surface-to-volume ratio and directed charge transfer. In recent years, reduction dechlorinations by TiO2nanotube arrays electrodes has attracted our attention, because it can avoid generating more toxic halogen-subsituted intermediates as well as the reduction products can be recycled.The process of photoelectrocatalytic (PEC) reduction dechlorinations could achieve with the help of photogenerated electrons which act as reducing agent and dechlorinating PCP. However, the practical application of TiO2nanotube arrays is significantly hindered due to lower quantum efficiency and high recombination efficiency between photoinduced electron and hole. Therefore, it is an important way to control the recombination between electrons and holes so that make effective chemical reaction happen to improve the PEC efficiency. In this dissertation, some works were carried out as follows:(1) The Ru/TiO2nanotube array electrodes were fabricated by electrochemical process of anodization, followed by a dipping and electrodeposition technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), UV-Vis diffuse reflectance spectra (DRS), surface photovoltage (SPV) analysis and electrochemical measurements were employed to characterize the Ru/TiO2nanotube array electrodes. The results indicate that the separation efficiency of the electron and hole was increased by Ru and Pd nanoparticles (NTs) modification.(2) The Ru-Pd/TiO2nanotube array electrodes were fabricated by the anodic oxidation method, followed by a dipping and electrodeposition technique. Through a series of physical characterization techniques, we proved that the Ru and Pd NPs were successfully deposited on the TiO2nanotube array electrodes. It reduced the recombination probability of photoinduced electron-hole and increased the utilization of UV light. Ru-Pd/TiO2nanotube array electrodes have high catalytic activity for PEC reduction of pentachlorophenol. We analyze the reaction intermediates by liquid chromatography-mass spectroscopy (LC-MS).(3) The Fe-Ni/TiO2nanotube array electrodes with different capacities were fabricated by the anodic oxidation method, followed by a dipping and electrodeposition technique. Through a series of physical characterization techniques, we proved that the proper Fe and Ni NPs depositing on the TiO2nanotube array electrodes could reduce the recombination probability of photoinduced electron and hole. The reduction degradation of PCP over Fe-Ni/TiO2nanotube array electrodes dipped and electrodeposited for5cycles is faster than that on TiO2nanotube array electrodes. We also analyze the reaction intermediates by LC-MS.