Hydrothermal Crystallization of TiO2 Nanotube Array Films

The highly ordered and uniform TiO2 nanotube array films were fabricated by anodic oxidation of titanium foil in KF-containing ethylene glycol solution. The as-prepared TiO2 nanotube array films were then hydrothermally treated, and the effects of hydrothermal treatment temperature and time on the surface morphology, crystallinity, and tubular structure of the nanotube films were investigated by X-ray diffraction and scanning electron microscopy. The results show that a transition from amorphous structure to anatase TiO2 could be found after hydrothermal treatment even for a short time (e.g. 3 h) at relatively low temperature (e.g. 210 ℃), and the crystallization degree increased with the improving of hydrothermal treatment temperature and time. The crystallization process of nanotube walls during hydrothermal treatment would lead to a decrease in inner diameter of the nanotubes and even a collapse of tubular structure when the crystallization degree was too high.