Oxidation of azo textile soluble dyes with hydrogen peroxide in the presence of Cu(II)–chitosan heterogeneous catalysts

Cu(II)–chitosan complexes were used as heterogeneous catalysts for degradation of five model azo textile dyes in aqueous solution with hydrogen peroxide. The most efficient catalyst contained 3.6% Cu2+ and the optimal reaction conditions were pH 7.0 and 50 mM of hydrogen peroxide. The rate of decolourisation was found to be directly dependent on the dye and hydrogen peroxide concentrations in the reaction mixture. Azo dyes containing the nitro group in their molecule were easier to oxidise than those lacking this group. Using optimal reaction conditions, 91.5% decolourisation of dye III (4 × 10−5 mol L−1) was obtained after about 20 min of reaction. However, 180 min were needed to decolorize about 85% of similar concentration of dye I. The only chemical structural difference is one nitro group on para position in relation to the azo bond.