Decolorization of synthetic dyes by the Fenton reagent and the Cu/pyridine/H2O2 system

Representative azo, triphenylmethane, heterocyclic and polymeric synthetic dyes have been decolorized by two biological non-ezymatic systems, copper/pyridine/H2O2 and the Fenton reagent. With the former system, intensive decolorization measured after 1 h was obtained with phenol red (89%), tropaeolin 00 (58%), Evans blue (95%), eosin yellowish (84%), and Poly B-411 (92%). The rate of decolorization was not affected by pH in the range of 3–9 and increased with increasing temperature. The use of the radical scavengers thiourea and superoxide dismutase showed that hydroxyl radicals rather than superoxide anions are involved in the reaction. Omission of pyridine led to a substantial decrease in the extent of decolorization (20–50% decolorization). The use of organic peroxide instead of H2O2 resulted in slightly slower decolorization, similar values of decolorization being obtained only after a 2-h incubation. Decolorization of the dyes by the Fenton reagent was also very effective but slower than that obtained with the first system. Except for phenol red and eosin yellowish, (decolorization 8% and 52%, respectively) the dyes were decolorized up to 99% after 1-day incubation.