Role of excess electrons in TiO₂ nanoparticles coated with Pt in reduction reactions studied in radiolysis of aqueous solutions

Surface modification of TiO₂ nanocrystallites in aqueous solution was carried out by reduction of chloroplatinic acid with TiO ₂ electrons (e_TiO2^-). The TiO₂ electrons had been generated through electron injection from 2-propanol radicals, hydrogen atoms, and hydrated electrons produced by γ or pulse radiolysis prior to the addition of the chloroplatinic acid. Upon addition of the latter, Pt⁰ clusters are produced by multistep reduction of the chloroplatinic acid on the TiO₂ surface. The present work concerns the material balance and chemical kinetics of the Pt₀ mediated reduction of water and H⁺ to molecular hydrogen by the TiO ₂ electron. Pt⁰ showed no effect on the rate of oxygen reduction, compared to bare TiO₂. The effect of surface Pt ⁰ on increasing photocatalytic yields, claimed by a number of laboratories, is apparently due to electron capture by the Pt⁰ rather than electron removal by oxygen.