Abstract

The photodegradation of dinitrosalicylic acid (DNS) by photoexcited uranyl ion was studied in aqueous solutions. The failure of DNS to degrade directly with light highlights the importance of the photoexcited uranyl ion in controlling the photochemical processes. Fluorescence quenching studies showed that an electron-transfer process from the DNS to the excited uranyl ion is involved leading to the formation of UO2+/DNS•+ radical pair complex as an initial step. Illumination of the UO22+/DNS solution in presence of oxygen results in mineralization of DNS. The results are explained on the basis of a catalytic cycle involving UO22+ ion and molecular oxygen that generates reactive superoxide O2•− anion and its conjugate acid HO2•. The efficiency of the photocatalytic cycle is enhanced markedly by addition of dilute NaOH solution.