In Situ Turning Pollutants Into Catalysts: A Phase-Transition Self-Catalysis Paradigm for Sustainable Water Treatment

Decentralized water treatment is constrained by high chemical demand and rapid catalyst deactivation, limiting the low-carbon remediation of waters containing heavy metals and organic micropollutants. Herein, we report a phase-transition-driven self-catalytic strategy that converts metal pollutants in situ into active catalysts for integrated purification and valorization. In a representative Ni²⁺/phenol system, peroxymonosulfate (PMS) shifts the Ni²⁺ ⇌ Ni(OH)₂ equilibrium toward NiOOH nanoparticle formation, which rapidly induces phenol polymerization and co-precipitation with residual Ni(OH)₂. Consequently, phenol is completely removed, while Ni²⁺ decreases from 28 to 0.08 mg L^-1 with ultralow PMS consumption. Mechanistic studies identify NiOOH as the reactive phase that oxidizes phenol to phenoxy radicals via proton-coupled electron transfer and proton transfer-electron transfer pathways. This strategy is highly effective for treating industrial phenolic wastewater and offers a modular platform adaptable to various metal ions (e.g., Co²⁺, Cu²⁺) and oxidants (e.g., NaClO, Peroxydisulfate). Combined with effective products recovery, it offers substantial economic and environmental advantages over existing methods. This work recasts pollutants from treatment targets into treatment agents, offering a fresh, and scalable route to sustainable water remediation.