Atomic microenvironment engineering of MOF-derived single-atom catalysts in advanced oxidation: From rational design to reaction pathway regulation

Metal–organic framework (MOF)-derived single-atom catalysts (SACs) are emerging as promising materials for advanced oxidation processes (AOPs) owing to their tailorable architectures, high atomic utilization, and well-defined active sites. However, how multilevel atomic-scale microenvironments govern catalytic pathways remains insufficiently understood. This review establishes a hierarchical framework that integrates the intrinsic structural microenvironment, defined by coordination configurations and local electronic structures, with the outer reaction microenvironment, governed by pore confinement and neighboring-site interactions. From this perspective, recent strategies for manipulating metal coordination, electronic structure, spatial confinement, and intersite cooperation are critically discussed, with emphasis on how these structural descriptors regulate charge transfer, oxidant adsorption and activation, metal redox cycling, reactive oxygen species evolution, and radical, nonradical, and other reactive-species pathways in photocatalytic and Fenton-like AOPs. Particular attention is given to establishing structure–pathway relationships rather than activity-centered correlations. Operando characterization and theoretical calculations are further assessed as complementary approaches for resolving dynamic active-site evolution and establishing mechanistic relationships. Finally, key challenges and opportunities toward accessible active sites, pathway-oriented microenvironment engineering, standardized evaluation, and realistic water-treatment applications are identified.