Fabrication of Ce-La-MOFs for defluoridation in aquatic systems: A kinetics, thermodynamics and mechanisms study

Abstract

Ce-La-MOFs composites was fabricated via the hydrothermal method, and considered an adsorbent to remove fluoride from aqueous solutions, and its property for defluoridation was discussed in this work. This study evaluated the ideal preparation molar ratio, adsorption period, and initial fluoride concentration. The adsorption mechanism was deduced from the analysis of thermodynamics, kinetics models, and characterization (SEM, XRD, FTIR, EDS, BET, TG). Furthermore, the impact of co-existing ions on the removal efficiency and regeneration of adsorbents was investigated. The studies have shown that the optimum conditions for defluoridation by Ce-La-MOFs were pH close to 3.0, the molar ratio of lanthanum-nitrate, cerium-nitrate, and 2-aminoterephthalic acid (La: Ce: ATPA) equal to 3:1:2, the initial F− concentration of 10 mg L−1, and the adsorption time of 120 min. Under these conditions, the removal efficiency can exceed 90%. The interference experiments suggested that the adsorbent material was highly selective for F−. The existence of most additional ions has a limited influence on the adsorption capacity, with only a minimal amount having an inhibitory effect. Kinetic and thermodynamic studies unveiled that the adsorption procedure is well-fitted with the Langmuir and pseudo-second-order models, and reaches a maximum Langmuir adsorption capacity of 138.64 mg g−1 at 50 °C. The adsorption process involved the integration of ion exchange and electrostatic interaction mechanisms. The regeneration cycle experiments showed that the Ce-La-MOFs composites had a favorable regeneration ability. After four regenerations, the adsorption capacity still reached 36.25 mg g−1 with 73% removal efficiency at C0 = 10 mg L–1.