Lawn-like Co3O4@N-doped carbon-based catalytic self-cleaning membrane with peroxymonosulfate activation: A highly efficient singlet oxygen dominated process for sulfamethoxazole degradation

The integration of advanced oxidation processes (AOPs) and catalytic membrane for filtration and peroxymonosulfate (PMS) activation was appealing for persistent organic pollutants removal. However, constructing a robust catalytic membrane with high reactivity and stability is highly desirable and still challenging. Herein, a kind of novel lawn-like Co3O4@nitrogen-doped carbon nanotube composites (Co3O4@NCNTs) by the pyrolysis of ZIF-67 in-situ grown on g-C3N4 was unprecedentedly designed, and then immobilized into protonated g-C3N4 (g-CN) membrane to construct Co3O4@NCNTs/g-CN membrane by vacuum-assisted filtration, where active sites were completely exposed for oxidants and target pollutants. As expected, the degradation rate of sulfamethoxazole (SMX, 20 mg/L) in Co3O4@NCNTs-0.5 (0.01 g/L)/peroxymonosulfate (PMS, 0.2 g/L) system was 0.2224 min−1, which was 35.9 times higher than that of Co3O4@NCs (0.0062 min−1) derived from ZIF-67. Besides, it was found that the introduction of lawn-like Co3O4@NCNTs significantly improved the surface hydrophilicity of g-CN membrane, consequently, the permeation flux of the Co3O4@NCNTs/g-CN membrane showed a 16.7 folds increase. Ultimately, the synergistic degradation and filtration process of catalytic membrane not only exhibited superior catalytic and self-cleaning property in humic acid (HA)/SMX coexistence system, but also significantly reduced the leaching concentration of Co2+ (0.016 mg/L) after 5 runs compared to that of Co3O4@NCs/PMS system (0.041 mg/L), demonstrating improved stability and reusability. Furthermore. scavenger experiments and electron paramagnetic resonance (EPR) tests verified that the SMX degradation was dominated for the coexistence of multiple reactive active species (ROS, SO4·−, ·OH and 1O2) while 1O2 was a major contributor. Overall, this work offered new prospects in developing novel catalytic self-cleaning membrane.