Comparative study of electrochemical oxidation for dye degradation: Parametric optimization and mechanism identification

Present study investigates the direct and indirect electrochemical (EC) oxidation of malachite green (MG) dye in acidic and basic medium using RuO2-TiO2 and Pt coated Ti mesh electrodes (Ti/RuO2-TiO2 and Ti/Pt electrodes). The effects of process parameters such as current density (j), initial pH (pHo) and NaCl (electrolyte) concentration (m) during the EC oxidation were also examined. This study investigates the effect of dissolved chlorine, chlorate, chlorite, and chlorine dioxide formed during EC oxidation at different pH. Active sites of electrodes surface promote the production of OH radicals ((OH)-O-center dot). Synergistic effect of active chlorine species and (OH)-O-center dot radicals significantly enhanced the indirect EC oxidation of MG dye solution with Ti/RuO2-TiO2 anode. Gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC), color and chemical oxygen demand (COD) were used to identify the EC oxidative degradation mechanism with both electrodes. Acidic pH was found to promote the dye degradation. Under optimum condition, MG dye was completely decolorized and 98% COD removal was obtained after 140 min of EC treatment. Based on the intermediate and by-products identification, it seems that MG dye degradation occurred via N-methylation and conjugated structure destruction. (C) 2016 Elsevier Ltd. All rights reserved.