Oxidative Degradation of Azo Dyes in Aqueous Solution by Water-Soluble Iron Porphyrin Catalyst

Abstract

Textile and food industries produce a significant volume of effluents containing azo dyes and other pollutants. These effluents are serious environmental threats, and new methods for their treatment and for the degradation of azo dyes are thus attracting much attention. The current study deals with the oxidative degradation of azo dyes by meso-tetrakis(1-methylpyridinium-4-yl)prophyrinatoiron(III), [FeIII(tmpyp)], and meta-chloroperoxy benzoic acid (m-CPBA) in aqueous solution at room temperature. The catalytic degradation of azo dyes was investigated by using rapid-scan stopped-flow spectrophotometry as a function of solution pH, [catalyst], [m-CPBA], [dye] and [surfactants]. To obtain mechanistic insight, the reaction between [FeIII(tmpyp)] and m-CPBA was also studied in aqueous solution in absence of azo dyes. Spectral analyses and kinetic data show that [FeIII(tmpyp)] is transformed into the transient intermediate [FeIV(O)(tmpyp)].+ (a compound I analog) within 20–30 ms followed by the formation of relatively stable [FeIV(O)(tmpyp)] (a compound II analog). Batch experiments reveal that the dye degradation rate is influenced by the solution pH and the concentrations of [FeIII(tmpyp)], m-CPBA, dye, and surfactants. On the basis of the kinetic and spectroscopic data, a mechanistic scheme for the dye degradation reaction and a steady-state rate equation are proposed. The products resulting from oxidative degradation of the azo dye amaranth have been analyzed by HPLC-UV-HRMS.