Adaptive structural modification of Zr-based MOF-808 via solvent and ligand engineering for enhanced fluoride ion adsorption efficiency

The rapid development of industries such as new energy and photovoltaic has led to the generation of a large amount of industrial fluorine wastewater, posing serious threats to water environment and human health. To address this issue, MOF-808 adsorbent was synthesized by controlling the synthesis conditions and modifying the ligand structure. Batch adsorption experiments were conducted by varying experimental conditions, including type of adsorbent, pH, wastewater concentration, adsorption time, temperature, and interfering anions. The adsorption behavior of MOF-808-AA towards fluoride ions was well fitted by the Elovich non-linear kinetic model, as well as the Freundlich and Temkin non-linear isotherm models, indicating that the adsorption behavior was influenced by multiple mechanisms other than just intraparticle diffusion. Thermodynamic results suggested a spontaneous exothermic monolayer chemical adsorption process. Under the conditions of pH 6.0 and T = 298 K, MOF-808-AA exhibited a maximum adsorption capacity of 84.65 mg/g for fluoride ions. Characterization techniques, as well as quantum chemical analysis was employed to analyze the adsorption behavior and predict the reaction sites. The potential mechanism can be summarized as the formation of new bonds between MOF-808-AA and the adsorbed fluoride ions, as well as the weak intermolecular interactions such as hydrogen bonding and vdW forces. Furthermore, MOF-808-AA demonstrated satisfactory reusability and excellent chemical stability during the cyclic process. These findings suggest the potential application of MOF-808-AA for removing fluoride ions from wastewater.