Process optimization and mechanism study of acid red G degradation by electro-FentonFeox process as an in situ generation of $H_2O_2$

Abstract

Dye-contaminated wastewaters are industrial wastewaters that are difficult to treat using traditional biochemical and physicochemical methods. In the present work, the acid red G was removed as a model pollutant by the electro-Fenton process for the first time. The anode and cathode used by the electro-Fenton process were iron plate and graphite felt, respectively. It was concluded that under the optimal conditions of current density = 20 mA $cm^{–2}$, pH = 3 and initial $Na_2SO_4$ concentration = 0.2 M, the removal rate of acid red G (ARG) with an initial concentration of 300 mg L–1 could reach 94.05% after 80 min of electrolysis. This reveals that the electroFenton-Feox process used in this work has an excellent removal efficiency on acid red G. The required reagents $(Fe^{2+} and H_2O_2 )$ were generated by the electrode reaction, while the optimal generation conditions and mechanism of •OH, $H_2O_2$, and $Fe^{2+}$ were investigated. By testing •OH, $H_2O_2$, and $(Fe^{2+} agents at different pH and current densities, it was revealed that the electro-Fenton reaction was most efficient when the current density was 20 mA cm–2, and the pH was 3. Moreover, the removal rate of ARG is consistent with first-order reaction kinetics.