Photooxidation of cellulose acetate and cellobiose by the uranyl ion

Abstract

The photooxidation of cellulose acetate by uranyl nitrate in acetone solutions has been investigated. Studies of the effect of the polymer on the uranyl luminescence showed an initial increase in intensity, followed by quenching. This is interpreted in terms of competition between complexation of uranyl ions by the polymer and dynamic quenching. In the quenching region, Stern–Volmer kinetics are followed. Upon photolysis of the solution, a decrease in viscosity was observed, consistent with chain scission. However, there was no sign of formation of reduced uranium species, suggesting that they are reoxidised by molecular oxygen. Model studies were carried out with cellobiose and it was confirmed that the luminescence quenching involves both dynamic and static processes. Photolysis of aqueous solutions of cellobiose and uranyl nitrate or perchlorate led to formation of uranium(V) and a decrease in pH. Upon interruption of photolysis, uranium(V) was seen to disproportionate. Yields of reduced uranium species were higher in degassed than aerated solutions, consistent with their oxidation by molecular oxygen in the latter case. Organic radicals were detected by electron paramagnetic resonance spectroscopy upon photolysis of cellulose acetate saturated with uranyl nitrate. The mechanism of photooxidation is suggested to involve hydrogen atom abstraction from the substrate by excited uranyl ions.