Oxidative Degradation of Azo Dyes in Combined Fenton-like Oxidative Systems

Abstract

Kinetic patterns of the degradation of Methyl Orange (MO) dye are studied upon persulfate (PS) and quasi-monochromatic UV radiation (mercury-free source: KrCl-excilamp, 222 nm, referred to below as UV) treatment in the presence or absence of iron ions. Oxidative systems can be placed in the following order according to the efficiency and rate of dye degradation: {PS/UV/Fe2+} > {PS/UV} > {PS/Fe2+} > UV > PS. It is found that only in the combined {PS/UV/Fe2+} system does the total conversion of MO occur, but its deep mineralization in an aqueous solution is also possible. When this happens, the removal of total organic carbon can be as high as 77%. Inhibitors of radical reactions are used to show that both hydroxyl and sulfate anion radicals participate in oxidative degradation in the combined systems {PS/UV/Fe2+} and {PS/Fe2+}, and the role of sulfate anion radicals is dominant in the process. The possibility of using quasi-monochromatic UV radiation for persulfate activation in the oxidative degradation of azo dyes is shown experimentally.