Mechanistic Insights and Design Strategies for Hydrogel/Aerogel Sorbents in Remediation of Per- and Polyfluoroalkyl Substances

Per- and polyfluoroalkyl substances (PFAS) have been used for several decades in various sectors, including aerospace, construction, the military, and the production of goods, among others. This widespread use has significantly contaminated water bodies globally. Several government agencies and organizations are trying to develop advanced technologies such as oxidation, membrane filtration, adsorption, and ion-exchange resin to capture these chemicals and thus mitigate their impacts. Adsorption has proven to be a highly attractive method for removing PFAS, involving activated carbon, silica, bioadsorbents, anion-exchange resin, hydrogels, and nonion exchange polymers. Among different adsorbents, hydrogels are the most effective adsorbents for removing these forever chemicals due to their highly porous structure, reuse and regeneration ability, and ease of functionalization with specific groups for effective binding with PFAS molecules. Keeping in view their tremendous potential, this Review critically reviews the potential of underexplored hydrogel/aerogels-based sorbents developed from synthetic polymers as well as biopolymers. The use of different cross-linkers, co-monomers, inorganic and organic additives, and surface functionalization techniques on the PFAS removal ability of the resulting hydrogels/aerogels under varying pH, background species concentration, PFAS concentration, and temperature was thoroughly discussed. Furthermore, the underlying adsorption mechanisms (ionic, hydrophobic, hydrogen bonding, and F-F interactions) of hydrogels and aerogels for PFAS adsorption from a molecular perspective were also examined. Finally, the challenges inhibiting the large-scale production of these adsorbents and the scope of ionic fluorogel and thermosensitive hydrogels have also been thoroughly reviewed.