Pt-Enhanced Mesoporous Ti3+/TiO2 with Rapid Bulk to Surface Electron Transfer for Photocatalytic Hydrogen Evolution.

Pt-doped mesoporous Ti3+ self-doped TiO2 (Pt-Ti3+/TiO2) is in situ synthesized via an ionothermal route, by treating metallic Ti in an ionic liquid containing LiOAc, HOAc, and a H2PtCl6 aqueous solution under mild ionothermal conditions. Such Ti3+-enriched environment, as well as oxygen vacancies, is proven to be effective for allowing the in situ reduction of Pt4+ ions uniformly located in the framework of the TiO2 bulk. The photocatalytic H2 evolution of Pt-Ti3+/TiO2 is significantly higher than that of the photoreduced Pt loaded on the original TiO2 and commercial P25. Such greatly enhanced activity is due to the various valence states of Pt (Ptn+, n = 0, 2, or 3), forming Pt-O bonds embedded in the framework of TiO2 and ultrafine Pt metal nanoparticles on the surface of TiO2. Such Ptn+-O bonds could act as the bridges for facilitating the photogenerated electron transfer from the bulk to the surface of TiO2 with a higher electron carrier density (3.11 × 1020 cm-3), about 2.5 times that (1.25 × 1020 cm-3) of the photoreduced Pt-Ti3+/TiO2 sample. Thus, more photogenerated electrons could reach the Pt metal for reducing protons to H2.