Anodization Fabrication of Highly Ordered TiO₂Nanotubes

This Article focuses on the fabrication of highly ordered nanotubes and some novel nanostructures of titania (TiO2) with a two-step anodization method. The first-step anodization was actually a pretreatment of the Ti foil surface and provided well-ordered imprints that served as a template for the further growth of nanotubes. As a result, the TiO2 nanotubes growing in the second-step anodization appreciably outperformed those fabricated with the conventional one-step Ti anodization in terms of size uniformity and arrangement orderliness. The parameters of the anodization were then modulated to obtain more complex structures. When the voltage in the second-step anodization was lower than that in the first-step anodization, a lotus root-shaped TiO2 nanostructure, in which each imprint contained several smaller nanopores, was achieved. When the second anodization was further divided into two stages, double-layered nanotube arrays were synthesized. They contained two distinctly separated parts, i.e., the bamboo-shaped upper one and the smooth-walled lower one. These results have demonstrated the effectiveness and controllability of the two-step anodization method in producing high-quality TiO2 nanotubes, which are believed to have potential applications in such fields as solar cells, photonic crystals, and hydrogen storage.