Photo-induced absorption spectroscopy (PIAS) study of the kinetics of water oxidation by P25 TiO2 using periodate as an electron acceptor

Abstract

Photoinduced absorption spectroscopy, PIAS, coupled with the measurement of dissolved O2, % O2, is used to probe the kinetics of water oxidation by periodate, photocatalysed by a P25 TiO2 film on glass. The rate of the photocatalysed oxidation of water by periodate, rO2, depends upon ρ0.9, where ρ is the UV irradiance. In contrast, PIAS reveals the steady-state change in the absorbance of the film, ΔAbsSS, is proportional to ρ0.22, where ΔAbsSS is a direct measure of the steady-state concentration of photogenerated holes on the surface of the photocatalyst particles, [h+]SS. The combination of this data reveals rO2 is proportional to [h+]SS4, which is rationalised in terms of an electrochemical oxide path reaction mechanism with the combination of two surface adsorbed O atoms as the rate determining step. The potential of PIAS to provide an invaluable direct insight into the mechanism of photocatalytic reactions by powders is discussed briefly.