Effect of annealing temperature on structural and bonded states of titanate nanotube films

A conversion from commercial titania (TiO2) nanoparticles to nanotubes was achieved by a hydrothermal method. The titanate nanotube (titanate) film was then deposited on a Si (001) substrate using an electrophoretic deposition (EPD) technique. The post hydrothermal treatment was then carried out by annealing the films at 300–1000°C for 30min in the static air. A major amount of intercalated sodium (Na) in as-synthesized titanate nanotubes was removed during the electrodeposition process. The collapse of the tubular structure can be seen clearly when annealed above 500°C. X-ray diffraction data indicate a significant increase in the anatase phase peak intensity with annealing temperature. O 1s peak is found to be built up of subpeaks of H2O, −OH, and Ti–O. Annealing results in an increase of the Ti–O peak intensity while other peaks disappear. Clear changes in the O 1s peak positions, symmetry, and shift towards lower energy (0.8eV) are evident with the increasing annealing temperature. The doublet spectral lines of Ti 2p were found separated by an energy of 5.6eV. Photoelectron spectroscopy show that during the annealing treatment, the chemical bonds such as H2O and −OH are removed from the titanate films as well as converting the bonded states of titanate to that of titania.