Stoichiometric hydrogen peroxide versus hypochlorite generation via dual-cell continuous flow system enables singlet oxygen-dominated phenol oxidation.

Abstract

Current electrochemical processes utilizing singlet oxygen (¹O₂) for wastewater treatment face limitations due to inefficient hydrogen peroxide (H₂O₂) generation and uncontrollable stoichiometric ratios between H₂O₂ and hypochlorite (ClO^-). To address these operational bottlenecks, this study developed a dual-cell continuous-flow system that decouples the production of H₂O₂ and ClO^- to degrade phenol and other organic contaminants. The system features a natural air diffusion cathode (ADC) for energy-efficient H₂O₂ generation without aeration and a dimensionally stable anode (DSA) for active chlorine production. By optimizing the applied current ratio (ADC:DSA = 2:1), an optimal 1:1 H₂O₂/ClO^- stoichiometric molar ratio was achieved. This precise control successfully maximized ¹O₂ production (steady-state concentration: 5.77 ± 0.24 × 10^-10 mM), resulting in a 97.9% removal of phenol under optimal conditions. Additionally, the system achieved removal rates of 71.6% for bisphenol A and 81.3% for sulfamethoxazole. Furthermore, the ¹O₂-dominated oxidation pathway suppressed the formation of chlorinated byproducts by 24-48% compared to a conventional single-cell electrochemical method. Overall, this engineered dual-cell architecture effectively overcomes the intrinsic bottlenecks of conventional electro-oxidation, establishing a robust, ¹O₂-driven paradigm for the safe and selective pretreatment of refractory wastewaters.