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

Abstract

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 N₂ and H₂ 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 °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.