Multi-capture site design in a bifunctional Zr-MOF for broad-spectrum and efficient removal of short- and long-chain PFASs

Abstract

The escalating threat of per- and polyfluoroalkyl substances (PFASs) to human health and the ecological environment has intensified the need for advanced porous adsorbents. Herein, we report a series of mono- and bifunctionalized MOF-808 materials grafted with fluoroalkyl and amino groups, systematically evaluating the contribution of the trifluoromethylalanine (TFMA) moiety toward broad-spectrum PFAS uptake. Batch adsorption experiments reveal exceptional capacities of MOF-808-TFMA for perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA), reaching 1558.3 and 605.4 mg g⁻¹, respectively, with equilibration achieved within 30 minutes. Over 85% removal efficiency was maintained even at trace concentrations, alongside strong anti-interference capability. The material retained 81% of its initial efficiency after five regeneration cycles using methanol–ammonia. Combined experimental characterization and density functional theory (DFT) calculations elucidate a multi-synergistic site mechanism: amino-enabled hydrogen-bonding and electrostatic interactions dominate short-chain PFAS capture, while fluorophilic and hydrophobic interactions enhance long-chain PFAS adsorption. Notably, we identify for the first time an “adsorption trough” for perfluorohexanoic acid (PFHxA), attributed to a pore-size–molecular-dimension critical matching effect (ΔS° < 0), providing a theoretical early warning for avoiding synergistic failure in adsorbent design. The bifunctional MOF-808-TFMA demonstrates outstanding PFAS removal performance in real wastewater, offering a foundational strategy for the rational design of next-generation PFAS adsorbents.