Effect of humic acid binding on sulfonamide degradation using CO2-based carbon nanotubes activated by persulfate: Modified interfacial electron transfer

Binding effects of dissolved organic matter (DOM) to antibiotics on redox processes have received much attention. However, most studies have focused on the role of humic acid (HA) in homogeneous systems, its binding interactions with antibiotics within carbon-based persulfate (PS) activation systems remain poorly understood. This study addresses this knowledge gap by investigating the impact of HA complexation on sulfonamide antibiotic degradation within a model CNT-CO 2 /PS non-radical system. The fluorescence quenching effect and ultraviolet visible spectral shifts of HA confirmed its binding effect with sulfonamide antibiotics. When the binding effect occurred, the degradation rate of the system for sulfamethoxazole increased by 21.5% compared with that of unbound, the degradation rate of sulfadiazine decreased by 15.9%, while sulfamerazine and sulfapyridine remained basically unchanged. Electrochemical impedance spectroscopy and Tafel analysis identified the CNT-CO 2 nano-interface as the primary site for electron transfer. Furthermore, cyclic voltammetry and linear sweep voltammetry revealed that the electron transfer intensity between the CNT-CO 2 /PS system and pollutants changed significantly when the binding effect occurred. By building a theoretical computational model of HA with sulfonamide antibiotics, the changes before and after binding was also examined. Consequently, the binding effect of HA affected the degradation rates primarily by modifying the direct electron transfer capacity between the CNT-CO 2 /PS system and sulfonamide antibiotics. This study elucidates a key mechanism, modulation of direct electron transfer by HA complexation, governing sulfonamide antibiotic fate in advanced carbon/persulfate oxidation processes.