Studies on pH-dependent color variation and decomposition mechanism of Brilliant Green dye in Fenton reaction

Abstract

Degradation of Brilliant Green (BG) dye has been studied using Fenton reagent in the dark environment. The intensity of dye color was pH dependent with maximum absorbance at pH 6. N-de-alkylation caused dye decomposition which resulted in the reduction of absorbance. The rate of BG dye decolorization increased with an increase in the H2O2 and Fe2+ concentration. The presence of background ions commonly found in an industrial dyeing wastewater suppressed the efficiency of color, COD and TOC removal within 9 %. There was about 2.9-fold increase in biodegradability index after 30 min of reaction. The proposed mechanism showed the routes of dye degradation with low errors (−0.88 to 0.49 g mol−1) with respect to the exact mass. Dye degradation began with N-de-ethylation, and later was further cleaved to aromatic-amine, -acid, -alcohol and -additive products. Hydroquinone was originated by hydroxylation of N,N-diethyl aniline. An equilibrium cycle among quinone, hydroquinone and Fe(III)-hydroquinone was exhibited through the formation of charge transfer complex.