Photoreduction of uranyl ion in aqueous solution .1. With ethanol in sulphuric acid solutions

Photoreduction of UO22+ with ethanol (EtOH) in H2SO4 solutions has been studied by an electrochemical quantitative analysis of U-IV formed as a final product, The quantum yield phi(U-IV) of U-IV increased rapidly at [EtOH] up to 0.5 mol dm(-3) and then reached a maximum phi(U-IV) under oxygenated conditions was almost one-half of that under deaerated conditions. In order to explain these experimental results, phi(U-IV) was expressed on the basis of both formation of an encounter complex between excited UO22+ (*UO22+) and EtOH and a successive reaction of UO22+ with alpha-hydroxyalkyl radical formed after the complex formed. Kinetic parameters for the quenching of *UO22+ by EtOH were derived from a plot of phi(U-IV)(-1) vs. [EtOH](-1) and checked by the measurements of the photon emission from *UO22+ with a time-resolved laser and steady state light excitation. It was confirmed that the proposed photoreduction mechanism could reproduce the experimental results.