Effective defluoridation of water using nanosized UiO-66-NH₂ encapsulated within macroreticular polystyrene anion...

Environmental concerns associated with the efficient defluoridation of contaminated water remain a substantial challenge. In this work, a new nanocomposite, UiO-66-NH₂@PS⁺, was successfully fabricated via in situ precipitation of a water-stable metal-organic framework (UiO-66-NH₂) inside a commercial polystyrene anion exchanger PS⁺. The as-formed nanocomposite UiO-66-NH₂@PS⁺ was characterized using various morphological methods, which demonstrated that nanosized UiO-66-NH₂ was homogenously dispersed within the inner pores of PS⁺. Batch adsorption experiments indicated that UiO-66-NH₂@PS⁺ exhibited outstanding adsorption performance for fluoride over a broad pH range of 3.0-8.0. The saturated adsorption capacity of fluoride at 298 K was 27.5 and 32.8 mg/g for pH 6.5 and 4.5 with the adsorbent dosage of 0.5 g/L and initial concentration of 5-80 mg/L. Moreover, the utilization rate of active adsorption sites of UiO-66-NH₂ was greatly improved after encapsulation. The XPS study indicated that the integrated effects of specific inner-sphere coordination and ligand exchange between fluoride and UiO-66-NH₂ might be the dominant adsorption mechanism. Fixed-bed tests indicated that the UiO-66-NH₂@PS⁺ column could successively produce clean water with bed volumes of 350 and 70 ([F^-] <1.5 mg/L) from simulated fluoride-pollution water at pH 4.5 and 8.0, with a liquid velocity of 20 mL/h, and an empty bed contact time (EBCT) of 15 min, which was higher than that of the other materials. In addition, the exhausted UiO-66-NH₂@PS⁺ was regenerated and reused for 5 times through complete regeneration, highlighting the potential feasibility of defluorination in practical applications.