Beyond radicals: harnessing non-radical pathways in MOF-based functional materials for water purification

Non-radical pathways have attracted increasing attention in diverse heterogeneous advanced oxidation processes (HAOPs) employing metal-organic framework (MOF)-based functional materials owing to their advantages including excellent pollutant degradation performance, ultra-high selectivity, low oxidant consumption, strong anti-interference capability, and broad pH applicability. However, the complexity of the various formation and conversion pathways, along with the available identification methods, has led to an unclear understanding of the non-radical formation mechanisms mediated by MOF-based catalysts. This work systematically summarizes the characteristics, formation pathways, and identification methods of different non-radical pathways across various AOP systems involving singlet oxygen (¹O₂), high-valent metal-oxo species (HVMOs), electron transfer process (ETP), direct oxidative transfer process (DOTP), and surface-bound radicals. Furthermore, recent advances in MOF-based catalysts for the catalytic degradation of organic pollutants are presented, with an emphasis on the relationship between the structure of MOF-based catalysts and the corresponding non-radical generation mechanisms. Finally, current drawbacks and future outlooks regarding non-radical pathways in MOF-based catalysts for water purification are discussed. This review aims to provide valuable insights to advance the development of organic pollutant elimination using MOF-based functional materials.