PFAS removal by ultra-low loads of a metal-organic cage

The central bottleneck in per- and polyfluoroalkyl substance (PFAS) remediation lies in the large amounts of adsorbent typically required for effective PFAS removal, which ultimately dictates regeneration burden, energy demand, cost, and waste generation. This constraint reflects a fundamental chemical shortcoming of bulk adsorbents, in which PFAS uptake proceeds through nonspecific physisorption rather than controlled, stoichiometric binding. Here, we present two Metal-Organic Cages (MOCs)-MOC-Pd-NO₃ and MOC-Pd-H₂PO₄-that address this challenge through molecularly controlled, counter-anion-regulated ion exchange. These discrete cages achieve quantitative removal of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) across seven orders of magnitude in concentration, reaching 99.8% removal at 10⁴ ppm and 93.9% at 10³ ppt. Remarkably, PFAS capture occurs at unprecedented [MOC]/[PFAS] molar ratios of ∼0.05 at high concentrations and ∼10 at environmentally relevant levels. The MOCs loadings demonstrated here are several orders of magnitude lower than what is required by state-of-the-art adsorbent materials. Each cage exchanges its native counter-anions to bind 22-32 PFAS molecules, and remains recyclable, retaining up to 98% uptake capacity after ten cycles. These results establish MOCs as a general molecular platform for efficient, regenerative PFAS sequestration, and recognize counter-anion identity as a key chemical design parameter for next-generation sustainable remediation strategies.