Preparation And It's Mechanism Of TiO₂ Nanotubes Via Anodization In Halide Ions Containing Electrolyte

The unique physical chemistry properties of TiO2 nanotube films derived from high surface-to-volume ratios and specific architectures, making them of great applicable potential in the fields of photocatalysis, gas sensing, photoelectrolysis, and photovoltaics. Therefore, the fabrication of TiO2 nanotube films and the exploration of their potential in practical application have been attracting more and more attention. As a simple electrochemical method, anodization has been widely used in preparation of valve metal (Ti, Zr, Nb, W, Ta and Hf) and aluminum oxide nanotubes or nanoporous films. In the present work, TiO2 nanotubes or nanoporous film was fabricated via anodization of pure Ti in halide ions containing electrolyte. In order to optimize anodization process, morphology and crystalline of TiO2 nanotubes as well as anodization mechanism was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD).TiO2 nanotubes film was fabricated via anodization of pure Ti in fluoride ions containing electrolyte. Morphology of TiO2 nanotubes prepared via Ti anodization in the organic electrolyte showed that the wall thickness of tube reduced with the increase of distance from the bottom. The reason was considered to be chemical dissolution of nanotubes in the solution. At the same time, nanowires covered the nanotubes were thought to be formed by rupture of the upper part of nanotubes in smallest thickness under surface stress.The formation mechanism of TiO2 nanotubes in chloride containing electrolyte was explored through the study of the preparation parameters'effect on pit corrosion of titanium surface and the formation of nanotubes. Formation of appropriate amount of Cl2 led to the formation of nanotubes. Pit corrosion and formation of nanotubes in different areas of titanium surface formed in different time. the chlorine ions in aqueous solution anodizing. At the same time, we recognized that the surface stress, resulted by oxidation of Ti, led to the change of morphology and direction of nanotubes. Due to the formation of nanotubes in different time, nanotubes in different orientation appeared on the surface. On the basis of research in anodization in halogen ions containing electrolyte, both two-step anodization method and ethanol bath were used to fabricate freestanding nanotubes. The mechanism of two-step anodization was discussed. Nanoporous TiO2 was prepared via anodization of Ti substrate from ethanol bath method under the same conditions. The freestanding nanotubes membrane was used to study the crystalline of TiO2 nanotubes through XRD and TEM. The result shows that the third generation TiO2 nanotubes is a mixture of amorphous and anatase TiO2 .