Highly ordered self-organized TiO2 nanotube arrays prepared by a multi-step anodic oxidation process

Abstract

Highly ordered TiO2 nanotube arrays were prepared using a self-templating multi-step anodic oxidation process in a fluoride-containing electrolyte. The microstructures, chemical compositions, and phases of the self-organized TiO2 nanotube arrays were analyzed by FESEM, XPS, and XRD, respectively. Hexagonal packing density in TiO2 nanotube arrays significantly improved after the the multi-step anodic oxidation. The area densities of the hexagonal TiO2 nanotube arrays increased approximately 3 times from the first to second step in the anodic oxidation steps process (4.9 mu m(-2) to 16.4 mu m(-2)), but there was no difference between the second and third step (16.4 mu m(-2) to 16.0 mu m(-2)). The as-anodized TiO2 nanotube array had an amorphous structure and it transformed to an anatase phase during the annealing process at 450 A degrees C for 1 h. The as-anodized TiO2 nanotube arrays adsorbed the fluoride, hydrocarbon groups (CH), hydroxyl groups (OH, C-OH), and carboxyl groups (O = C-OH) on their surfaces.