KINETICS OF THE LASER-INDUCED PHOTOREDUCTION OF U(VI) IN AQUEOUS SUSPENSIONS OF TIO2 PARTICLES

The reduction of U(VI) to U(IV) in aqueous suspensions of TiO2 (pH 4.5 -7) was investigated by time-resolved laser-induced fluorescence (TRLI F). The laser irradiation was used both to provide the energy necessar y for the photogeneration of charge carriers and to monitor the kineti cs of the oxidation state change directly in the measurement cuvette b y exciting the U(VI) fluorescence. The U(VI) photoreduction was found to involve only adsorbed uranium species. The TRLIF measurements of U( VI) fluorescence lifetimes and individual emission fluorescence spectr a allowed a selective identification of the Various U(VI) hydro comple xes present in the aqueous-phase and adsorbed on the mineral surface. A reaction mechanism is proposed based on the kinetics results obtaine d at pH 7 where adsorption of the hydroxocomplex (UO2)(3)(OH)(5)(-) on TiO2 is complete.