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

Kaichao Yang; Ibrahim M Abu-Reesh; Zhen He

doi:10.1016/j.jhazmat.2022.130126

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

J Hazard Mater. 2023 Jan 15:442:130126. doi: 10.1016/j.jhazmat.2022.130126. Epub 2022 Oct 5.

Authors

Kaichao Yang¹, Ibrahim M Abu-Reesh², Zhen He³

Affiliations

¹ Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA.
² Department of Chemical Engineering, Qatar University, Doha, Qatar.
³ Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA. Electronic address: zhenhe@wustl.edu.

PMID: 36303354
DOI: 10.1016/j.jhazmat.2022.130126

Abstract

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, H_ads) 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.

Keywords: Chlorinated organic compounds; Detoxification and mineralization; Electrochemical; Reduction-oxidation; Wastewater treatment.