Optimization of a three-electrode system for electrochemical reduction–oxidation of 4-chlorophenol with response surface methodology

Chlorophenols are ubiquitous and resistant pollutants to traditional treatment that produce detrimental effects on humans. The aim of this investigation was to examine the Pd/graphene electrocatalytic reduction–oxidation process of 4-chlorophenol using a three-electrode system composed of two Pd/graphene gas-diffusion cathodes and one Ti/IrO2/RuO2 anode. By means of a single factor experiment, this study determined the influence of factors such as current density, electrolyte concentration, pH, and aerated condition. Optimal conditions were obtained by response surface methodology. Results showed that 4-chlorophenol degradation increased with rise in current density, but decreased with elevation in electrolyte concentration. 4-Chorphenol degradation was unfavorable to the redox reaction in per-acid or alkaline solution. A small quantity of 4-chlorophenol and other aromatic compounds remained when bubbling hydrogen alone. Feeding oxygen subsequently further oxidized residual 4-chlorophenol and the related compounds. The optimal variables were as follows: current density, 45 mA cm−2; Na2SO4 electrolyte concentration, 0.03 mol L−1; initial pH, 7; electrolysis time, 120 min (60 min for bubbling hydrogen and then 60 min for air). Under these conditions, the degradation efficiencies of 4-chlorophenol were 94.9% (cathodic chamber 1), 95% (cathodic chamber 2), and 94.7% (anodic chamber).