Fouling, Deactivation, and Self-Healing of Coordinatively Unsaturated Metal Sites in MOF-Derived Catalysts During Real Water Treatment

Coordinatively unsaturated metal sites (CUSs) are central to the adsorption, electron transfer, and oxidant-activation steps that make metal–organic-framework (MOF)-derived catalysts attractive for water purification. Their open coordination environment, however, also creates an intrinsic durability problem: the sites that bind peroxides, periodate, sulfite, ozone, oxygen, or target pollutants can be competitively occupied by natural organic matter, phosphate, carbonate, chloride, transformation products, and water itself. This review develops a site-resolved framework for interpreting fouling, deactivation, regeneration, and self-healing under realistic aqueous conditions. Evidence from Fe-, Co-, Cu-, Ni-, Ti-, Zr-, Ce-, and mixed-metal MOFs, MOF-derived carbons and oxides, single-atom catalysts, heterojunctions, and catalytic membranes is integrated to distinguish four frequently conflated phenomena: loss of pollutant conversion caused by solution-phase scavenging, reversible occupation of CUSs, irreversible rewriting of the first coordination sphere, and transport fouling at the particle or membrane scale. Particular attention is given to diagnostic evidence based on oxidant utilization, dissolved-metal balance, X-ray absorption and photoelectron spectroscopies, pore accessibility, transformation-product analysis, and continuous-flow operation. Regeneration is classified as physical cleaning, chemical reactivation, structural reconstruction, or genuine self-healing. The review concludes with quantitative recovery metrics, a matrix-ladder validation protocol, and design rules that couple local coordination chemistry with pore architecture and reactor operation. The central proposition is that durability should be reported as preservation and recoverability of a chemically identified active state, rather than inferred from a small number of batch reuse cycles.