The effects of sodium content and hydrogenation of TiO2 nanotubes on photocatalytic activity

The effects of sodium content and hydrogenation of TiO2 nanotubes on their photocatalytic activity were investigated. TiO2 nanotubes with different contents of sodium were prepared by an alkaline reflux method, followed by washing with different concentrations of acid. When a hydrogen thermal treatment was applied to the nanotubes, the white nanotubes with and without sodium would transform into blue polyhedral and light yellow chain-like structures, respectively. UV-vis absorption spectra indicated that a higher absorption in the visible light range was obtained for the blue polyhedral structure. Interestingly, an amorphous surface layer and Ti3+ species appeared and became more pronounced when the sodium was removed completely. This led to the formation of a defect energy band belt, which not only narrowed the band gap but lowered the rate of recombination of photo electrons and holes. As a consequence, a higher rate of photocatalytic decomposition of methanol for hydrogen evolution under visible light illumination were obtained. (C) 2018 Elsevier B.V. All rights reserved.