Iron Oxychloride (FeOCl)-Based Materials as High-Performance Heterogeneous Fenton-like Catalysts: Crystal Structure, Reaction Mechanisms, Material Engineering, and Environmental Applications

Iron oxychloride (FeOCl) has recently attracted considerable attention as a high-performance heterogeneous Fenton-like catalyst. Its layered Fe-O-Cl coordination environment enables rapid FeIII/FeII redox cycling and efficient activation of H2O2, thereby promoting the generation of reactive oxygen species (ROS) for pollutant degradation. This review summarizes recent progress in FeOCl-based materials, including their crystal structure, optical, electrochemical, magnetic and other physicochemical properties, synthesis strategies, catalytic mechanisms, and environmental applications, with particular emphasis on experimental evidence and density functional theory (DFT) calculations. Special attention is given to pH-insensitive H2O2 activation, visible-light-assisted Fenton-like reactions, heterojunction construction, elemental doping, intercalation engineering, membrane-supported catalysts, morphology engineering, and flow-through electro-Fenton configurations. FeOCl-based catalysts have demonstrated outstanding performance in degrading dyes, antibiotics, phenolic compounds, endocrine-disrupting compounds, and other recalcitrant pollutants, while also showing potential in heavy-metal adsorption, selective oxidation, and energy-related applications. Finally, remaining challenges concerning catalyst stability, iron leaching, scalable synthesis, realistic water matrices, byproduct toxicity, and reactor integration are discussed to guide the rational design of practical FeOCl-based catalytic systems.