Enhanced visible light and photocatalytic performance of TiO2 nanotubes by hydrogenation at lower temperature

Protonated titanate nanotubes were chosen as a precursor in a hydrogenation process. Owing to the high capacity for molecular hydrogen storage of nanotubes, TiO2 nanotubes can be hydrogenated through thermal treatment under N-2 and H-2 mixed flow at lower temperature. A series of hydrogenated TiO2 nanotubes and nanobelts were synthesized and characterized by XRD, UV-vis, TEM, EPR and XPS. The results showed that the hydrogenated TiO2 nanotubes possess tiny and uniform diameters of 8-10 nm and walls thicknesses of 2-3 nm, and were mainly anatase. The anatase TiO2 nanotubes transformed to TiO2-B nanobelts when the hydrothermal temperature was higher than 150 degrees C. The light absorption of hydrogenated TiO2 nanotubes was expanded to visible light. However, air-TiO2 and hydrogenated TiO2 nanobelts only absorbed ultraviolet light. According to XPS and EPR analysis, hydrogenated TiO2 nanotubes displayed stable core-shell structures, in which the surface was mainly stoichiometric TiO2 and the core was non-stoichiometric TiO2 with Ti3+ and oxygen vacancies. The adsorption and photocatalytic performance were evaluated by the removal rate of phenol. Based on a pseudo-first order kinetic model, the degradation rate constant was obtained with the regression analysis. The highest degradation rate constant of hydrogenated TiO2 nanotubes was 5.2 times higher than air-TiO2. In comparison, the degradation rate constants of hydrogenated TiO2 nanobelts were much lower than air-TiO2. The results showed that the precursor with nanotube structure can be hydrogenated easily at lower temperature compared with nanobelts, resulting in the photocatalytic activity of hydrogenated TiO2 nanotubes being enhanced drastically.