Dynamique des réactions de transfert d'électrons induites par la lumière à la surface de semi-conducteurs colloïdaux
Studies have been carried out on aqueous colloidal suspensions of semiconductors, principally by using laser flash-photolysis techniques, in order to scrutinize in detail the dynamics of light-induced charge transfer reactions occuring at the solid-electrolyte interface. Preparation of sols of good transparency allows the use of all fast spectroscopic methods usually reserved for homogeneous systems and enables the monitoring of the temporal behavior of transient species involved during light absorption and electron transfer events. Under these conditions, one was able to observe the following reactions : a) the reduction of different acceptors in solution by conduction band electrons of titanium dioxide under band-gap irradiation, b) the oxidation of halides by valence band holes of TiO2 and α-Fe2O3, and c) the charge injection in the solid from visible light excited sensitizers. Results have lead in most cases to the development of simple models describing the dynamics of interfacial electron transfer. The direct spectroscopic observation of trapped electrons in the conduction band of the semiconductor has afforded a handle for quantitative evaluation of electron-hole pairs recombination kinetics in pure or doped TiO2 particles. Dynamics of charge carriers out of equilibrium has also been entered upon by the measurement of its influence on the electron transfer quantum yield.