Preparation of Well-Aligned TiO₂ Nanotubes with High Length-Diameter Aspect Ratio by Anodic Oxidation Method.

This paper focused on the influence of various oxidation parameters such as electrolyte composition, reaction time, calcination temperature and current change on the morphology and structure of TiO2 nanotube arrays. It was found that ammonium fluoride with a high viscosity reduced the diffusion rate of fluoride ions and significantly increased the length of TiO2 nanotubes, creating nanotubes with ordered arrays and uniform diameters. Meanwhile, the time of anodic oxidation determined the length of TiO2 nanotube arrays. Well-aligned nanotube arrays could be obtained after 0.5-2.5 h of oxidation. In addition, when the oxidation temperature was about 30 °C, the TiO2 nanotube arrays achieved the optimal uniformity and the maximum length-diameter aspect ratio. The morphology and quality of the TiO2 nanotubes fabricated were estimated through current as a function of reaction time. Consequently, formation mechanism of TiO2 nanotube arrays was investigated undergoing three major periods. The findings of this study can shed some light on the optimal conditions for preparing well-aligned TiO2 nanotube arrays with high length-diameter aspect ratio.