Nanoconfined Cobalt Single‐Atom Catalysts with Tailored Coordination Enabling Near‐Complete Electron Transfer in Reactive Filtration

Abstract Coordination environment engineering in single‐atom catalysts (SACs) has emerged as a powerful strategy for enhancing catalytic efficiency in peroxymonosulfate (PMS) activation, offering precise electronic structure modulation at active sites. However, challenges such as limited accessible reactants and high oxidant input continue to constrain their practical implementation in water decontamination. Here the scalable fabrication of a nanoconfined catalytic membrane featuring SA‐Co sites on phosphorus‐doped carbon nitride is reported by pyrolyzing metal‐organic framework precursors (SA‐Co/PCN). The incorporation of phosphorus into the secondary coordination shell of SA‐Co sites fine‐tunes the electronic structure of cobalt centers, facilitating a transition from singlet oxygen to a direct electron transfer pathway, while the nanoconfinement significantly enhances the utilization efficiency of trace PMS and reactive oxygen species. The SA‐Co/PCN membrane achieves a sulfamethoxazole degradation rate of up to 0.11 ms −1 and sustains ≈ 100% removal over 154 h, outperforming most reported catalysts. It also exhibits robust performance in degrading electron‐rich pollutants, stability in diverse environmental conditions, and applicability to real wastewater treatment. This work underscores the synergy between secondary coordination and nanoconfinement in SACs, offering a versatile platform for developing efficient and stable membranes for sustainable water treatment applications.