Synthesis of Mg/Al Layered Double Hydroxides for Adsorptive Removal of Fluoride from Water: A Mechanistic and Kinetic Study

Herein, we report the synthesis of Mg/Al-CO₃ layered double hydroxides (LDHs) by the urea hydrolysis method under hydrothermal conditions at different aging times. The LDHs were characterized by different microscopic, spectroscopic, diffractometric, and thermal analysis techniques. The as-prepared LDHs were then used as adsorbents for the removal of fluoride ions from water. The adsorption process was systematically studied in terms of influences of pH, interaction time, temperature, adsorbent loading, fluoride ion concentration, and the effect of coexisting anions to understand the ideal conditions for adsorption. The adsorption process primarily followed pseudo-second-order kinetics. The Langmuir monolayer adsorption capacities of different adsorbents are in the range of 15.13–27.03 mg g^–1 at 303 K. The hydrothermal aging time has a negative impact on the adsorption capacities of the LDHs. The as-prepared LDHs are reusable up to five cycles of the fluoride ion adsorption–desorption process.