Mechanism of Enhanced Fluoride Adsorption Using Amino-Functionalized Aluminum-Based Metal–Organic Frameworks

Due to the increasing fluoride concentrations in water bodies, significant environmental concerns have arisen. This study focuses on aluminum-based materials with a high affinity for fluorine, specifically enhancing metal–organic frameworks (MOFs) with amino groups to improve their adsorption and defluorination performance. We systematically investigate the factors influencing and mechanisms governing the adsorption and defluorination behavior of amino-functionalized aluminum-based MOF materials in aqueous environments. An SEM, XRD, and FT-IR characterization confirms the successful preparation of NH₂-MIL-101 (Al). In a 10 mg/L fluoride ion solution at pH 7.0, fluoride ion removal efficiency increases with the dosage of NH₂-MIL-101 (Al), although the marginal improvement decreases beyond 0.015 g/L. Under identical conditions, the fluoride adsorption capacity of NH₂-MIL-101 (Al) is seven times greater than that of NH₂-MIL-101 (Fe). NH₂-MIL-101 (Al) demonstrates effective fluoride ion adsorption across a broad pH range, with superior fluoride uptake in acidic conditions. At a fluoride ion concentration of 7 mg/L, with 0.015 g of NH₂-MIL-101 (Al) at pH 3.0, adsorption equilibrium is achieved within 60 min, with a capacity of 31.2 mg/g. An analysis using adsorption isotherm models reveals that the fluoride ion adsorption on NH₂-MIL-101 (Al) follows a monolayer adsorption model, while kinetic studies indicate that the predominant adsorption mechanism is chemical adsorption. This research provides a scientific basis for the advanced treatment of fluoride-containing wastewater, offering significant theoretical and practical contributions.