Degradation of 4-chlorophenol through cooperative reductive and oxidative processes in an electrochemical system

Electrochemical treatment can be an effective approach for degrading recalcitrant organic contaminants because its anode/cathode produces powerful oxidizing/reducing conditions. Herein, through the cooperation of the cathodic reductive and anodic oxidative processes, 4-chlorophenol (4-CP) was successfully degraded in an electrochemical system. TiO2 nanotube arrays (TNTAs)/Sb-SnO2 and TNTAs/Pd were successfully prepared and served as the anode and cathode electrodes, respectively, to generate oxidative (hydroxyl radical, ·OH) and reductive (chemically adsorbed hydrogen, Hads) agents. The sequential reduction-oxidation (SRO) process provided a reasonable degradation pathway that accomplished reductive detoxification in the cathode and oxidative mineralization in the anode. The SRO mode achieved dechlorination efficiency (DE) of 86.9 ± 3.9% and TOC removal efficiency of 64.8 ± 4.2% within 3 h and under a current density of 8 mA cm−2, both of which were significantly higher than those obtained in the sequential oxidation-reduction or the simultaneous redox modes. The increment of current density and reaction time could improve 4-CP degradation performance, but a high current density would decrease the cathode stability and a longer reaction time led to the generation of ClO4-. This study has demonstrated that sequential reduction-oxidation can be an effective and tunable process for degrading recalcitrant organic contaminants.This paper was made possible by NPRP grant # [ NPRP13S-0109-200029 ] from the Qatar National Research Fund (a member of Qatar Foundation). K. Y. would like to thank the support from Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis. The findings achieved herein are solely the responsibility of the authors