Electrochemical and Photochemical Oxidation of Cationic Dyes: A Comparative Study

This study reports on comparative performance of electro-Fenton and photo-Fenton processes in the mineralization of three cationic dyes: BB41, BR46 and BY28. Primary objective was to determine the optimal conditions for both processes. It has been shown that the mineralization rate by electro-Fenton process depends on operating parameters such as applied current density, catalyst concentration, pH, etc. It was also observed that dyes degradation by hydroxyl radicals follows pseudo first-order reaction kinetics. Under the optimal operating conditions ([Fe 3+ ] = 0.2 mM, j = 3 mA cm -2 , and pH = 3), electro-Fenton process leads to an almost mineralization of dyes solutions reaching 93, 86 and 77% of TOC abatement for BB41, BR46 and BY28 respectively. The dye mineralization rate during photo-Fenton (UV/Fe 3+ /H2O2) process is a function of reagent doses, and their concentration ratio R = [H2O2]/[Fe3+]. Thus, mineralization rates obtained are around 95, 93 and 85% for BB41, BR46 and BY28 respectively for a treatment time of 5 h with a ratio R = 10 and [Fe3+] = 0.2 mM. The mineralization of a mixture of the three cationic dyes was also studied in a second step. Results showed that both photo-Fenton and electro-Fenton processes are able to reach almost complete mineralization rates. Finally the electro-Fenton process is considered the more efficient and interesting technique due to its environmentally friendly character with low energy consumption and no use of chemical reagents.