Proposal for highly efficient electrochemical discoloration and degradation of azo dyes with parallel arrangement electrodes

Abstract

In this research, different electrochemical advanced oxidation processes (EAOPs), such as electro-oxidation (EO), electro-Fenton (EF) and photoelectro-Fenton (PEF) were aimed to enhance the degradation efficiency of two azo dyes: Chocolate Brown HT (CB) and Eriochrome Black (EB), as model industrial dyes. Boron doped Diamond (BDD) electrodes were used as an anode and a cathode for EAOPs production. The capacity of individual effects of each process and coupling were evaluated as functions of the decolorization and mineralization of industrial dye solutions. The azo dye solutions were completely decolorized under acidic conditions pH2.8–3.0. The mineralization of the mixture of solutions was improved in the following order: EO<EF<PEF, due to the gradual increase in the production of free hydroxyl radicals (OH), PEF is more potent due to the photolysis of the oxidation products. Chemical oxygen demand abatement of 91% for EO, 95% for EF and 98% for PEF processes were obtained, when using an applied current density (j) of electrolyzed solution of 20 mAcm−2. The azo dye decolorization for all treatments followed pseudo-first-order kinetics, suggesting the attack of a constant production of OH radicals in the solution under EF and PEF, and EO at the anode surface.