Structure‐Oriented Metal‐Organic Framework Activation via Proximal Oligoalkyl Quaternary Ammonium Grafting Enhances Long‐Chain PFAS Sorption

Abstract A structure‐oriented design of zirconium‐based metal‐organic frameworks (Zr‐MOFs) for long‐chain per‐ and polyfluoroalkyl substances (PFAS) is critically needed, as current efficacy faces limitations, including restricted micropore functionalization, limited coordination sites, and weak host–guest interactions. Here, we present a surface‐localized oligomeric grafting strategy to functionalize UiO‐66‐NH 2 with proximally arranged oligoalkyl‐quaternary ammonium (PAOQ) motifs, yielding UiO‐66‐ L 3 sorbent. Unlike conventional grafting approaches, the PAOQ motifs containing repetitive functional groups predominantly extend beyond surface pore layers, circumventing intrinsic grafting limitations of the MOF backbone and achieving a 2.2‐fold increase in group loading. This tailored architecture enables strong synergistic interactions through precise spatial alignment of quaternary ammonium moieties and conformationally flexible oligoalkyl chains, promoting dual‐mode coordination with long‐chain PFAS. Consequently, UiO‐66‐ L 3 exhibits rapid kinetics (equilibrium within 5 min) and high sorption capacities (403–1872 mg g −1 ) for long‐chain PFAS and derivatives, outperforming alkylated/quaternized analogs by up to 13.3‐fold. Density functional theory (DFT) calculations reveal that electronic redistribution induced by oligoalkyl segments enhances the electrostatic potential at adjacent ammonium centers, enabling chain‐length‐dependent selectivity with sorption coefficients ranging from 2.3 to 4.9. Our work highlights the critical role of surface chemistry modulation in Zr‐MOFs and advances structure‐oriented design of high‐performance sorbents for long‐chain PFAS and derivatives.