O₂-facilitated electrochemical oxidation of pollutants on oxygen-functionalized carbon nanotubes

Electrochemical oxidation offers a clean approach for wastewater treatment, yet challenges such as high energy demand and electrode deactivation impede its practical application. Here, we address these critical issues by integrating air into an electrochemical oxidation process, achieving deep mineralization of refractory aromatic pollutants at low potentials to avoid significant impact of water discharge. To enable active participation of atmospheric oxygen (O₂) in pollutant oxidation, oxygen-functionalized carbon nanotubes (OCNTs) were exploited to serve dual roles as the electrocatalyst and O₂ activator. The introduction of O₂ significantly enhanced the electrochemical oxidation of the probe pollutant, sulfamethoxazole (SMX), with its mineralization efficiency improved from 13.3 % to 80.1 %. The carbonyl (C=O) groups on OCNTs were identified to be the key sites for binding O₂, with formation of surface complexes that oxidized SMX via direct electron transfer. Density functional theory (DFT) simulations revealed the pivotal contribution of C=O in promoting the adsorption of O₂, fostering the formation of surface-O₂ complexes, and facilitating the oxidation of SMX by surface-O₂ complexes. The positive electric field applied during the electrochemical oxidation process promoted O₂ activation by reinforcing its interaction with the OCNTs surface. The air-enhancing strategy mitigated electrode fouling and proved effective across diverse water matrices, including high-salinity and natural organic matter-rich environments. These findings highlight the potential of oxygen-functionalized carbonaceous materials in advancing energy-efficient electrochemical oxidation systems for sustainable wastewater remediation.