Research PaperFull visible-light absorption of TiO2 nanotubes induced by anionic S22− doping and their greatly enhanced photocatalytic hydrogen production abilities

- The S22− has been successfully introduced into TiO2 nanotubes, which exhibit a serial of 9 nm S22−-doped TiO2 photocatalysts.
- The obtained S22− doped TiO2 nanotubes exhibit a full visible-light absorption (from 400 to 800 nm).
- The photocatalysts have a highest H2-production rate of 9610 μmol h−1 g−1 and the quantum efficiency (QE) reaches 19.8%.

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).

In this work, the S22−-doped TiO2 nanotubes present a special ability in a full visible light absorption, which greatly enhance photocatalytic activity under visible-light irradiation.224