Study Of The Controlled Synthesis, Growth Mechanisms And Properties Of Titania Nanotube Arrays/Nanocomposites

Titania is a typical transition metal oxide and has shown potential applications in the field of photocatalysis, photoelectric conversion, gas sensing because of its excellent physical chemical property and chemical stability. In 2001, synthesis of TiO2 nanotube arrays obtained by anodization of Ti was firstly reported by C.A. Grimes, and TiO2 nanotube arrays have attracted many attentions because of its special properties and huge applied potential.Compared with any other morphologic form of titania, TiO2 nanotube arrays are expected to exhibit novel and improved functional characteristics due to the higher specific surface area, stronger absorbability and so on. However, it still remains many challenges before TiO2 nanotube arrays become an economically feasible photocatalyst because of the defect that the absorption of visible light is very low. Therefore, a variety of methods have been developed for tailoring the photocatalytic properties of TiO2 nanotube arrays, such as doping with metallic or nonmetallic ions, modifying with noble metals or other semiconductors.TiO2 nanotube arrays were fabricated by anodic oxidation in this paper, and the morphology and structure of the TiO2 nanotube arrays were precisely controlled by tailoring the parameters of the anodization process. The photocatalytic property of TiO2 nanotube arrays was also tailored, and has been improved greatly under the visible light.This dissertation consists of 6 chapters:An introduction is given in chapter one, including the origin, significance of the subject, the author’s major contributions, and an overall review for the progress and situation of the controlled growth, modification and applications of TiO2 nanotube arrays.Chapter two illustrates the experimental materials and methods used in all parts of work in this dissertation, on the emphasis of the synthesis methods of the TiO2 nanotube arrays. Meanwhile, the method of modifying TiO2 nanotube arrays with carbon by hydrothermal treatment is introduced also in detail. In addition, the techniques for microstructure characterization and property testing are also demonstrated.In chapter three, the controlled growth and the growth mechanism of the TiO2 nanotube arrays are investigated. The synthesis of TiO2 nanotube arrays in HF aqueous solution, HF/ethylene glycol and HF/glycol/H2O electrolytes by anodization of Ti are investigated symmetrically. It is found that the electrochemical processes of anodization in variant electrolytes are different, which lead to the differences of the obtained TiO2 nanotube arrays. Meanwhile, the growth of TiO2 nanotube arrays are precisely controlled by tailoring the parameters of the anodization experiments, and the reason why the morphologies and structures of TiO2 nanotube arrays are influenced by the parameters is investigated symmetrically. Moreover, it is firstly found that the morphologies and structures of TiO2 nanotube arrays obtained by anodization from HF/ethylene glycol electrolyte can be controlled by tailoring the HF concentration of the electrolyte, which consummates the growth mechanism of TiO2 nanotube arrays. In addition, the photoelectric properties of TiO2 nanotube arrays with different morphologies and structures are investigated symmetrically, and it is found that the photoelectric property improves with the increase of the specific surface area of TiO2 nanotube arrays.In chapter four, the synthesis and the photocatalytic property of carbon-modified TiO2 nanotube arrays are investigated. For the first time, TiO2 nanotube arrays are successfully coated with a carbon layer thinner than 1 nm by hydrothermal treatment in glucose aqueous solution, and it is found that the concentration of glucose is a key factor for the modification of carbon. Moreover, the UV-Vis absorption, the photocatalytic and the photoelectric properties of the carbon-modified TiO2 nanotube arrays are investigated symmetrically. It is found that the photocatalytic property of the carbon-modified TiO2 nanotube arrays is improved greatly under the visible light. In addition, a conjecture is given for the photocatalytic process of the carbon-modified TiO2 nanotube arrays.In chapter five, the synthesis and the photocatalytic property of N-doped TiO2 nanotube arrays are investigated. The N-doped TiO2 nanotube arrays are fabricated by anodization of Ti foils which are plasma-nitriding treated. It is found that TiO2 nanotube arrays are doped with 1 at% Nitrogen, which leads to the N-Ti-O structure. Moreover, the UV-Vis absorption, the photocatalytic and the photoelectric properties of the N-doped TiO2 nanotube arrays are investigated symmetrically. It is found that the photocatalytic property of the N-doped TiO2 nanotube arrays is improved greatly under the visible light, and it is thought that the band gap of TiO2 nanotube arrays is decreased because of the N-doping, which lead to the increase of absorption of visible light and therefore the increase of photocatalytic property under visible light.All the research works mentioned in this dissertation are summarized in chapter seven. In addition, the author’s published papers finished during the doctoral student period are listed in the end the dissertation.