Sterically regulated biomimetic metal-phenolic antifouling interfaces for selective fluoride removal in NOM-rich...

Natural organic matter (NOM) can substantially hinder fluoride removal from groundwater and wastewater by competing for adsorption sites reducing adsorbent selectivity. Here, a lanthanum-based nanocomposite encapsulated by a metal-phenolic network (PSLa/MPN) was developed to enable NOM-resistant and highly selective fluoride removal. The crosslinked MPN layer acted as a transport-regulating interfacial barrier, restricting humic acid (HA) transport and surface accumulation through combined steric exclusion and electrostatic repulsion. Compared with the uncoated material, the MPN coating increased HA rejection by >50% and reduced HA diffusivity by 2.5-fold, while preserving fluoride access to the internal La-based adsorption sites. Consequently, PSLa/MPN maintained stable fluoride uptake and regeneration efficiencies above 95% at an elevated HA concentration of 80 mg DOC·L^-1. In contrast, benchmark La-based oxides showed 25-30% losses in adsorption capacity and a 52% reduction in reusability under NOM-rich conditions. In continuous fixed-bed experiments using multiple real water matrices, PSLa/MPN achieved a treatment capacity of 1273 bed volumes (BV) while consistently maintaining effluent fluoride concentrations below the World Health Organization guideline of 1.5 mg·L^-1. This performance was approximately 28-fold greater than that of commercial La-based resins, with favorable estimated treatment costs. The results demonstrate that MPN-based interfacial engineering is an effective strategy to enhance the selectivity and durability of fluoride adsorbents in NOM-rich, chemically complex waters.