Metal-Organic Frameworks, Covalent Organic Frameworks, and Metal-Covalent Organic Frameworks for Aqueous PFAS Adsorption: Synthesis, Structural Engineering, and Remediation Performance.

Per- and polyfluoroalkyl substances (PFAS) represent a critical class of persistent environmental pollutants that challenge conventional remediation technologies. Metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and the emerging metal-covalent organic frameworks (MCOFs) have attracted growing interest as tunable porous platforms for removing per- and polyfluoroalkyl substances (PFAS) from water. This review critically summarizes recent advances in the synthesis, structural characterization, and adsorptive performance of these three framework families. We examine key factors affecting adsorption, including solution chemistry and PFAS chain length, and elucidate the underlying mechanisms-hydrophobic/fluorophilic interactions, electrostatics, anion exchange, and coordination-through combined experimental and computational evidence. A comparative assessment evaluates adsorption capacities, kinetics, stability, and regenerability, identifying the distinctive advantages of each material class. Practical applications in fixed-bed columns and magnetic composites are also discussed. Finally, we highlight persistent challenges, particularly in the removal of ultrashort-chain PFAS, and outline future directions involving machine learning, defect engineering, and dual-functional adsorptive-catalytic platforms to guide rational adsorbent design.