Electrified activation of peroxymonosulfate using carbonaceous composite membranes for sulfamethoxazole removal: Treatment efficiency, mechanistic insights, and intermediate toxicity evaluation

Abstract

Metal-free carbonaceous materials can effectively activate peroxymonosulfate (PMS) for organic pollutant degradation by utilizing their surface active sites. In this study, an electrified membrane was fabricated using nitrogen-doped graphene (NG) sheets and carbon nanotubes (N-CNTs) to investigate the impact of different electrified modes on membrane performance for sulfamethoxazole (SMX) removal from water matrices. Characterization results indicated that NG/N-CNT mats exhibited superior electron transfer ability for PMS activation due to their abundant defects and nitrogen-doped species. When used as the cathode (Mode III), the carbon mats achieved a pseudo-first-order kinetic constant (k_obs) of 5.305 s⁻¹ (318.2 min⁻¹) for SMX removal, which was 51.63 % and 24.95 % higher than those in Mode I (no applied potentials) and Mode II (carbon anode), respectively. Reactive oxygen species identification revealed that non-radical pathways govern in-situ catalytic oxidation, with the relative contributions of surface-confined oxidation and singlet oxygenation significantly varying across different electrified modes. In contrast, Mode III significantly enhanced PMS activation, minimized the depletion of active sites (such as defects and pyridinic nitrogen), and reduced the accumulation of oxidation intermediates within the carbon mats. After continuous filtration of 12,000 bed volumes of carbon mats, Mode III still achieved over 85 % SMX removal from real river water while maintaining a high water flux of 116 L m^−2.h^−1.bar⁻¹. Intermediate composition analysis demonstrated that the filtrate from Mode III posed lower risks of acute and developmental toxicity compared to those from the other electrified modes. These findings provide a reliable and enhanced approach for efficient in-situ catalytic oxidation.