Full visible-light absorption of TiO^sub 2^ nanotubes induced by anionic S^sub 2^^sup 2-^ doping and their greatly enhanced photocatalytic hydrogen production abilities

TiO2, as a benchmark photocatalyst for hydrogen production through water splitting, has a relatively large band gap (3.2 eV for anatase and 3.0 eV for rutile) requiring UV light (290-400 nm) for electronic excitations from the valence band to the conduction band, hence utilizing only a small part of the solar spectrum. The construction of new electronic band gap, especially in the visible region (400-800 nm), is of great importance for improving TiO2 optical and photocatalytic properties. In this work, though it is deem metastable and can induce a broad visible-light adsorption in previous literatures, anionic S22- has been successfully introduced into TiO2 nanotubes, which is different from the previous works about S-doped TiO2 that contain only cationic S4+ and S6+. Resultantly, the S22- doped TiO2 nanotubes exhibit a full visible-light absorption (from 400 to 800 nm) and a greatly enhanced photocatalytic H2-production rate under visible-light irradiation (9610 µmol h-1 g-1, about 13.7 and 37 times of other cationic and anion S-doped TiO2 nanoparticles, respectively, almost highest in all the results reported previously in literatures of TiO2 doped with non-metal elements).