New insights on the role of NaCl electrolyte for degradation of organic pollutants in the system of electrocatalysis coupled with advanced oxidation processes

The role of sodium chloride (NaCl) in pollutant degradation in electrocatalysis coupled with advanced oxidation processes (EAOPs) system remains debatable and the formation of toxic chlorine-substituted byproducts during this process has raised growing concern. Herein, the role of NaCl electrolyte for the degradation of p-nitrophenol (4-NP) in the EAOPs (Co3O4/PMS/NaCl) system was identified. Different from the effect of mass transfer, the presence of NaCl electrolyte improved the 4-NP degradation efficiency and the degradation products were affected by the concentrations of peroxymonosulfate (0.01-8 mM) and Cl- (10-100 mM). Besides, different active species (SO4 center dot-, HOCl, or Cl-center dot/ClO center dot) with different amounts can be produced in the EAOPs systems with three typical PMS concentrations (0.01, 0.032 and 4 mM). Moreover, the formation of chlorine-substituted byproducts can be effectively avoided via adjusting the concentrations of PMS and NaCl to inhibit the formation of Cl-center dot/ClO center dot. Finally, this EAOPs system was used to degrade the kimchi processing wastewater and 34% of COD and 99% of TN were removed, revealing it has a good practical application. This study illuminates a new role of NaCl as the electrolyte for the degradation of organic pollutants in the EAOPs system for the first time.