Sustainable sodium alginate-La-Al-MOFs composite beads with enhanced mechanical strength for fluoride removal

Excessive fluoride has detrimental effects on human health and contributes to the contamination of aquatic and terrestrial environments. However, conventional powdered fluoride adsorbents often suffer from challenges such as poor recyclability and secondary pollution. Herein, a bimetallic Metal-organic frameworks (MOF) composite was synthesized employing a hydrothermal method and then embedded in sodium alginate to form sodium alginate-La-Al-MOFs composite beads (SAMB) gel spherical material. The fluoride adsorption performance of SAMB was systematically evaluated under varying conditions. SAMB demonstrated strong removal performance over an extensive pH spectrum, ranging from 3 to 9, with optimal performance observed at pH 3. At an initial fluoride concentration of 20 mg/L and an adsorbent dosage of 1 g/L, SAMB achieved a maximum fluorine removal efficiency of 87.6 %. Fluoride adsorption followed monomolecular layer chemisorption as confirmed by Langmuir and pseudo-secondary kinetics. The large surface pores of SAMB enabled rapid removal of fluoride within 15 min with a maximum adsorption capacity of 46.67 mg/g at 298.15 K. Regeneration experiments displayed the adsorption efficiency of the gel spheres adsorbent only decreased by 29 % after four times of reuse. The adsorption mechanism revealed that SAMB fluorine adsorption was dominated by ion exchange and electrostatic attraction. These findings demonstrate that SAMB serves as an effective and environmentally benign adsorbent for aqueous fluoride removal, offering a sustainable alternative to conventional treatment methods. • La-Al-MOFs were used as novel synthetic adsorbents for efficient fluoride removal. • SAMB showed excellent fluoride removal with high stability and renewability. • The large crack-like pores on the surface of SAMB were favorable for adsorption. • Electrostatic attraction and ligand exchange were the main adsorption mechanisms.