Effects of sodium content and calcination temperature on the morphology, structure and photocatalytic activity of nanotubular titanates.

Titanate nanotubes (TNT) were prepared via a hydrothermal treatment of TiO(2) powders (P25) in a 10 M NaOH solution at 150 degrees C for 24 h and subsequently washed with HCl aqueous solution of different concentrations (0.1, 0.01, and 0.001 N). Samples with different contents of remnant sodium in nanotubes were characterized, as synthesized and after heat-treatment, by transmission electron microscopy, X-ray diffraction, and nitrogen adsorption-desorption isotherms. The photocatalytic activity of TNT was evaluated by photocatalytic oxidation of basic dye (basic violet 10 (BV10)) in water solution. It was found that if the sodium was not completely exchanged with proton, the removal of sodium increased the specific surface area (and pore volume), while the thermal stability was reduced. When the sodium content of TNT was approximately 0 wt% (nearly complete proton exchange), the nanotubular structure of titanates might be destroyed. The effects of the alterations of microstructures induced by the exchange of sodium and heat-treatment on the photocatalytic activity of TNT were discussed with the variations of specific surface area, pore volume, and the amounts of anatase phase in TNT.