MXene-Based Catalysts for Peroxymonosulfate Activation: Structure-Pathway Relationships, Water-Matrix Effects, and...

MXenes have emerged as promising catalytic platforms for peroxymonosulfate (PMS) activation because their metallic conductivity, tunable surface terminations, defect-rich lamellar structures, and compositional flexibility enable efficient electron transfer and active-site engineering. However, the catalytic behavior of MXene-based PMS systems is highly dependent on surface chemistry and interface configuration, and the relationships among synthesis, structural descriptors, reactive pathways, and environmental applicability remain insufficiently clarified. This review summarizes recent advances in surface- and defect-engineered MXene-based catalysts for PMS activation, with emphasis on surface- and defect-dependent structure-activity relationships. First, MXene synthesis and modification strategies, including fluoride-assisted etching, fluorine-free routes, termination regulation, defect engineering, doping, single-atom anchoring, and heterostructure construction, are discussed in terms of their influence on accessible active sites and interfacial electron-transfer properties. Second, radical and nonradical PMS activation pathways are critically analyzed, highlighting how terminations, vacancies, metal sites, and conductive interfaces regulate the generation of SO4•-, •OH, 1O2, and direct electron-transfer processes. Third, the performance of MXene-based catalysts in complex water matrices is evaluated, including pH tolerance, ion effects, natural organic matter interference, immobilization, membrane integration, and continuous-flow operation. Finally, environmental stability, metal leaching, oxidation-derived transformation, by-product risks, and safe-by-design considerations are assessed. This review aims to provide a materials-centered framework for regulating the surface chemistry, defect structures, and catalytic interfaces of MXenes to couple efficient PMS activation with practical and environmentally responsible water purification.