Degradation of Alizarin Red S under mild experimental conditions by immobilized 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine–Mn(III) as a biomimetic peroxidase-like catalyst

Abstract

Alizarin Red S, an industrially important anthraquinone dye coming from alizarin sulfonation, is a widespread polluting dye, whose inexpensive and environmental friendly elimination from effluents is a serious challenge. In this study we report its decoloration and partial mineralization by H 2O 2 in the presence of the heterogeneous catalyst obtained from 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine–Mn(III) immobilized on a modified silica support bearing imidazole functionality. The bleaching process was efficient and took place under very mild experimental conditions, where it mainly led to phthalic acid. Some operational features of the catalytic reaction are described and a chemical mechanism for the bleaching is proposed. Most efficient decoloration was seen at pH 7, the process most probably passing through an unstable anthradiquinone. Also some kinetic features of the catalyst have been studied, and a substrate saturation behavior for both hydrogen peroxide and the dye was observed and quantitatively determined.