Mg/Al-LDH-Cl– for Fluoride Removal from Water: High-Capacity Adsorption and Recyclable Regeneration

This study hydrothermally synthesized chloride-intercalated Mg/Al layered double hydroxide (Mg/Al-LDH-Cl–) for efficient fluoride removal, demonstrating high specific surface area and ion-exchange capacity. The material achieved rapid adsorption equilibrium (10 min) with a maximum capacity (59.60 mg·g–1) under neutral pH, following pseudo-second-order kinetics indicative of chemisorption-dominated Cl–/F– exchange. Regeneration with NH3/NaCl solution maintained 99.55% capacity after 5 cycles. Structural analyses revealed that fluoride adsorption was mainly realized by ion exchange between interlayer Cl– and F–, accompanied by weak coordination of surface hydroxyls; during the adsorption–desorption process, Al3+ always maintains octahedral coordination (AlO6) without structural collapse or coordination number change. In addition, the material showed strong resistance to coexisting anions. Compared with existing adsorbents, Mg/Al-LDH-Cl– combines high capacity, fast kinetics, and excellent cycling performance, providing an efficient and sustainable solution. This study not only elucidates the fluoride adsorption mechanism of LDH-based materials but also provides theoretical and technological support for their practical application.