Surface confinement of per-fluoroalkyl substances on an iron-decorated clay-cyclodextrin composite enables rapid oxidation by hydroxyl radicals

The removal and oxidation of seven perfluorinated compounds were studied in the presence of an iron-clay-cyclodextrin polymer composite (Fe-MMT-beta CD-DFB). The iron-clay backbone served as a heterogeneous Fen-ton catalyst, and the cyclodextrin polymer, cross-linked with polyfluorinated aromatic molecules, was used to promote removal and surface-confinement of the perfluorinated compounds. The composite exhibited superior adsorption (~90%) and efficient oxidation (> 70%) towards the high molecular weight PFAS: PFHpA, PFOA, PFNA, PFDA, and PFOS. The lower molecular weight PFAS: PFBA and PFHxA, showed lower adsorption affinity towards the composite but were almost completely degraded once adsorbed to the surface (> 90%). The oxidation was very rapid, reaching over 65% degradation of PFOA and PFOS within the first 10 min. EPR and probe measurements revealed that hydroxyl radicals were responsible for the high degradation rates. In addition, fluoride ion measurements coupled with TOC and LC/MS analysis showed high defluorination and mineraliza-tion rates of PFOA and PFOS (73.2% and 73.5%, respectively). The composite also displayed excellent perfor-mance in a mixed solution with the seven different PFAS, especially towards the degradation of high MW compounds. Furthermore, the composite's degradation activity remained stable even after five cycles of adsorption and degradation. Taken together, the results suggest that composites that promote surface confine-ment of the pollutants near the catalytic active sites can be used to efficiently remove and destroy highly recalcitrant pollutants under benign environmental conditions.

Automated summary

The study investigated the removal and oxidation of seven perfluorinated compounds using an iron-clay-cyclodextrin polymer composite. The composite showed excellent adsorption and efficient oxidation, especially towards high molecular weight compounds. It also exhibited stable degradation activity even after multiple cycles. These findings suggest that composites promoting surface confinement of pollutants can be used for efficient removal and destruction of highly recalcitrant pollutants.