Degradation of Monoazo Pigments Red 53:1 and Red 48:2 by Fenton, Photo-Fenton and UV/Peroxide Reactions

The degradation reactions of two monoazo pigments, namely, Red 53:1 and Red 48:2, by Fenton, photo-Fenton and UV/H2O2 systems have been studied. The efficiencies of the Fenton reactions increased with temperature, but the formation of solid agglomerates was observed when the reactions were carried out above 50 degrees C indicating a coagulant action of Fe+2 or Fe+3. Photo-Fenton reactions irradiated by sunlight presented the best rate constants for cleavage of the azo bond and the naphthalene rings. The UV/H2O2 system exhibited the highest efficiency with respect to the consumption of H2O2. The presence of a carbonyl group in the ortho position of the naphthol ring hampered the oxidation of pigment Red 48:2 by hydroxyl radicals. This finding may be explained in terms of the acceptor character of the COOH group, and suggests the formation of a complex containing two six-membered rings between Fe+3 and the pigment molecule.