Influence of calcination on photocatalytic properties of nonstoichiometric titanium dioxide nanotubes

The nonstoichiometric titanium dioxide nanotubular films were synthesized by the anodization of titanium foil in a solution of ethylene glycol and ammonium fluoride. The calcination of films at the temperatures of 200–600 °C led to the changes in their morphology, structure, phase composition, and properties. During the calcination, amorphous phase of titanium oxide in the prepared films was converted into anatase (space group I41/amd) at ca. 300 °C followed by the transformation of anatase to rutile (space group P42/mnm) at the temperatures above 500 °C. The optical band gap was decreased as the calcination temperature was increased due to the changes in stoichiometry and phase composition of nanotubular films. A complete mineralization of acetone vapor in a continuous-flow reactor using the nanotubular films was carried out for the first time. The photocatalytic activity of the film calcined at 500 °C in the reaction of acetone oxidation to carbon dioxide under visible light (λmax = 450 nm) was found to be 4 times higher than the activity of commercially available TiO2 P25. A high defectiveness and an extended surface were the reasons for an enhanced photocatalytic activity of the synthesized nanotubular films under visible light. [Display omitted] •The film of nonstoichiometric titanium dioxide nanotubes are grown.•Calcination led to phase, morphology, and properties transformation of the film.•Enhanced photocatalytic activity are result of efficient absorption of visible light.