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

Abstract

Surface modification of TiO2 nanocrystallites in aqueous solution was carried out by reduction of chloroplatinic acid with TiO2 electrons (e(TiO2)(-)). The TiO2 electrons had been generated through electron injection from 2-propanol radicals, hydrogen atoms, and hydrated electrons produced by gamma or pulse radiolysis prior to the addition of the chloroplatinic acid. Upon addition of the latter, Pt-0 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 Pt-0 mediated reduction of water and H+ to molecular hydrogen by the TiO2 electron. Pt-0 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 Pt-0 rather than electron removal by oxygen.