Brominated MIL-101/alginate composite hydrogels for efficient PFAS removal: Role of hydrophobic interactions and performance under continuous-flow conditions.

Per- and polyfluoroalkyl substances (PFAS), including perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS), are persistent contaminants that demand effective removal technologies. To overcome the practical limitations of powdered metal-organic frameworks (MOFs), including difficult recovery and limited compatibility with continuous-flow treatment, robust brominated MIL-101/alginate composite hydrogels (Br-MIL/Alg-4) were successfully fabricated for the adsorption of PFOS and PFHxS from water. Structural characterization confirmed the integration of Br-MIL-101 in the alginate matrix, while preserving the essential structural features of the MOF. Under the standard low-concentration batch condition (C0 = 1.0 mg/L), Br-MIL/Alg-4 exhibited experimentally determined adsorption capacities of 1.22 mg/g for PFOS and 0.95 mg/g for PFHxS, representing over a sevenfold enhancement relative to pristine alginate hydrogels (0.17 and 0.13 mg/g, respectively). Batch experiments demonstrated stable removal efficiencies and exceptional selectivity across various pH ranges, temperature and coexisting background anions. The results suggest that the enhanced uptake may reflect contributions from Br-associated and other non-electrostatic interactions, including possible hydrophobic interactions within the Br-functionalized framework. Continuous-flow column tests and multi-cycle methanol regeneration further demonstrated the reusability and continuous-flow compatibility of Br-MIL/Alg-4 under the tested conditions. These findings highlight the potential of Br-MIL/Alg-4 for treating PFAS-contaminated water and provide a basis for designing functionalized MOF-based composite adsorbents.