Study on the formation and photocatalytic activity of titanate nanotubes synthesized via hydrothermal method

Titanate and titania (TiO2) nanotubes were synthesized by hydrothermal method. The effect of NaOH to TiO2 ratio, reaction temperature, reaction time and annealing temperature on the formation of nanotubes was investigated using X-ray diffraction, field emission microscope and Transmission electron microscope. Titanate nanotubes with 10 nm diameter was formed for NaOH to TiO2 ratio >27 treated at 110 °C for 24 h. Increasing the synthesis temperature to 150 °C, the titanate nanotubes transformed to anatase phase and it was found minimum of 15 h is required for completing transformation from nanoparticles to nanotubular structure. With increasing annealing temperature, titanate nanotubes undergo dehydration and form anatase phase. Besides, the sintegration of the nanotubes was observed at 500 °C and the structure completely converted to nanoparticles at 600 °C. The photocatalytic activity of the sample was evaluated by degradation of methyl orange aqueous solution. The results indicate the photocatalytic activity of titanate is low and once the formation of anatase phase begins with increasing temperature, the photocatalytic activity increases dramatically. However, the deterioration in the tubular structure and increase in oxygen vacancies which act as a recombination centre of electron-holes with increasing annealing temperature need to be controlled to avoid the reduction in the photocatalytic behavior of anatase phase.