Efficient removal of short-chain perfluoroalkyl substances by cavity-directed aggregation in a molecular cage host

The removal of perfluoroalkyl substances (PFAS) from water is critical to protect human health and the environment. However, existing adsorbents often show low affinity toward short-chain PFAS, and a molecular-level understanding of binding is lacking. Here, we elucidate how a metal-organic cage traps both short- and long-chain PFAS in water, applying these insights to prepare mesoporous adsorbent that lowers PFAS their concentrations down to ppt levels. Host-guest studies reveal that PFAS electrostatically anchor to the Pd(II) centres of the host, whilst their fluoroalkyl chains aggregate in the hydrophobic cage cavity. X-ray crystallography reveals that the extent of this aggregation decreases as perfluoroalkyl chain length increases. Consequently, short-chain PFAS are bound with affinities comparable to their long-chain counterparts (log K ≥ 5). Doping mesoporous silica with ~1 wt% of the cage host yields an adsorbent that removes >98% of short- and long-chain PFAS at environmentally relevant concentrations (100 – 1000 ng/L) via flow-through filtration. The adsorbent can be readily regenerated while retaining activity over at least five cycles. These findings translate host–guest chemistry into an effective materials platform for PFAS remediation, including short-chain species that evade conventional removal methods.