Massive Ti3+ self-doped by the injected electrons from external Pt and the efficient photocatalytic hydrogen production under visible-Light

- This method avoids both Ti3+ exposing to air and the complex coating process for isolating oxygen.
- Mass Ti3+ ions are formed in the interior TiO2.
- The sample exhibits a high catalytic activity (up to 8117 μmol h−1 g−1) for hydrogen generation in water under visible light.

Ti3+ doping in TiO2 photocatalyst has attracted much attention due to its enhanced visible-light absorption and the decreased carrier recombination. However, the introduction of massive stable Ti3+ is still a great challenge because Ti3+ is easy to be oxidized in air. In this work, for the first time, a negatively charged core/shell TiO2/C nanostructure is prepared and then Pt0 atoms reduced by NaBH4 are loaded on its surface. Through a tracking test of the product's Zeta potential, XPS and FTIR measurements, it is found that the reductive electrons are produced due to the reaction between C and metal Pt, in which Pt exhibits a +2 chemical valence. And the lost electrons by Pt are transferred into the interior TiO2 through the carbon shell and reduce Ti4+ to Ti3+. This method avoids Ti3+ ions' exposing to air and overcomes the complex coating process for isolating oxygen, and provides a new facile one for efficiently Ti3+ self-doping. Through the following measurements, such as XPS, PL, EPR and Raman etc., it is proved that massive Ti3+ ions are formed in the interior TiO2, which greatly narrows the composite's band-gap (from 3.11 eV to 2.47 eV) and enhances the visible-light absorption. As a result, the as-obtained sample exhibits a larger carrier densities (13.9 × 1018 cm−3) and a higher photocatalytic activity under visible-light irradiation compared with those in other literatures: the rate of photocatalytic water splitting for H2 generation is up to 8117 μmol h−1 g−1.

The reductive electrons produced by the formation of Pt-C bond between C and Pt0 are transferred into TiO2 through the carbon shell of TiO2/C and then reduce Ti4+ to Ti3+.189