Upcycling Water Pollutants Into Long‐Chain Polymers via Synergistic Interfacial Dechlorination and Organic Radical Stabilization

High‐entropy oxides (HEOs) offer unusual electronic structures arising from lattice distortion, multimetal synergy, and high chemical stability. Here we report nitrogen‐doped carbon‐encapsulated HEOs catalysts (HEO@NC) synthesized by in situ carbothermal reduction for efficient pollutant removal and upcycling through selective oxidative polymerization. HEO@NC activates periodate via an electron‐transfer pathway coupled with surface‐adsorbed hydroxyl radicals, enabling the selective conversion of phenolic contaminants into polymeric products under extreme pH and strong ionic interference. Relative to metal‐free nitrogen‐doped carbon, HEO@NC markedly enhances periodate activation through interfacial electronic coupling and achieves a periodate utilization efficiency of 449.2%, far exceeding that of conventional mineralization. Density functional theory and experimental analyses reveal complementary roles of the HEOs components: Co/Ni provide periodate‐binding sites, Pt lowers the barrier for electron transport, Bi/Pb promote charge delocalization to stabilize polymeric intermediates, and oxygen orbitals strengthen periodate coordination and surface charge transfer via p – d hybridization. This synergy drives dechlorination‐coupled polymerization with sustained 4‐chlorophenol removal at ultralow oxidant consumption. HEO@NC further maintained > 95% efficiency with negligible metal leaching during 20‐day treatment of real coal chemical wastewater, demonstrating the potential for sustainable and low‐chemical‐consumption remediation of industrial‐relevant wastewater.