Fabrication of Transparent Pt-TiO₂ Sol and Its Photocatalytic Activity for Hydrogen Evolution

Titanium dioxide doped with Pt(IV) ions was synthesized via a sol-gel method, incorporating a sol purification process through dialysis. The doped Pt(IV) ions were reduced by UV light irradiation to obtain a transparent Pt-TiO₂ sol, with Pt(0) acting as a cocatalyst for hydrogen evolution. The hydrogen evolution activity of Pt-TiO₂ sol was evaluated under UV light irradiation using methanol as a sacrificial reagent. 0.05 atom % Pt-TiO₂ sol remained in the sol state without precipitation after 10 h of UV light irradiation. The amount of hydrogen produced after 10 h of light irradiation was 1195 μmol, with a turnover number (TON) of 664.1, a turnover frequency (TOF) of 66.4 h^-1, and an apparent quantum yield (AQY) of 0.86%. The sol-gel synthesis from the molecular level is thought to result in Pt ions being doped inside the TiO₂ particles, maintaining high dispersibility by suppressing particle growth due to the aggregation of Pt(0) during the UV reduction of Pt(IV) ions. These results show that the Pt-TiO₂ photocatalyst has a high renewable energy factor because it can be synthesized at room temperature, and the aggregation of Pt-TiO₂ particles is suppressed by making full use of a sol-gel method.