Janus Reaction-Zone Catalytic Membrane for Sequential and Selective Degradation of Multiple Micropollutants: Performance and Mechanistic Insights

Efficiently treating complex water matrices containing multiple micropollutants remains a major challenge in advanced water purification. Here, we developed a carbon nanotube-nickel Janus reaction-zone membrane (JRM) via chemical vapor deposition to enable sequential activation of nonradical pathways by spatially separated reaction zones. Sequential utilization of ¹O₂ in the Ni-layer reaction zone and direct electron transfer (DET) in the CNT-layer reaction zone was achieved for the selective and efficient degradation of multiple micropollutants. The JRM/PMS catalytic filtration system exhibited remarkable robustness toward mixtures of antibiotics and phenolic pollutants, achieving 100% removal of phenol (Ph) and 93.7% removal of oxytetracycline (OTC) in complex water matrices. A sequential two-stage degradation mechanism was elucidated through intermediate product analysis and density functional theory (DFT) calculations. In the first stage, DET-mediated oxidation in the CNT-layer reaction zone selectively attacked the phenolic hydroxyl group of Ph, driving dehydrogenation and generating phenoxyl radicals, with fused-ring compounds identified as key intermediates. In the second stage, ¹O₂ in the Ni-layer reaction zone preferentially targeted the hydroxyl group on the benzene ring of the OTC with the highest electrophilic Fukui index, initiating degradation through dehydroxylation and decarbonization. DFT calculations further corroborated the sequential DET and ¹O₂ oxidation pathways, showing thermodynamically favorable degradation of Ph and OTC with energy releases of 1.52 eV for Ph and 5.57 eV for OTC. Overall, this study establishes a Janus reaction-zone strategy on an inorganic membrane interface, enabling the selective and efficient removal of multiple pollutants and providing insight into guiding the design of catalytic membranes toward complex water matrices.