Moesbauer Study of the Kinetics of Fe3+ Photoreduction on TiO2 Semiconductor Powders

Article abstract of DOI:10.1021/j100260a025

The kinetics of the photoreduction of Fe³⁺ to Fe²⁺ via illuminated TiO2 particles suspended in ferric chloride electrolyte has been studied by 57Fe Moessbauer spectroscopy.The semiconductor powder-liquid electrolyte slurry was quench-frozen after specific illumination periods to generate samples amenable to Moessbauer spectroscopy.The rates and equilibrium conversion of Fe³⁺ reduction were obtained for five TiO2 particle-electrolyte systems: (1) intrinsic anatase powder; (2) intrinsic rutile powder; (3) intrinsic anatase powder with a facile hole acceptor added to the electrolyte; (4) reduced, n-type anatase; and (5) platinized, n-type anatase powder.A simple kinetic model, based on competition between the forward reduction of Fe³⁺ and the back oxidation of Fe²⁺, and controlled by semiconductor band/redox couple energetics, is able to account for the observed differences in Fe³⁺ photoreduction for the five systems.