Howaida M. Abd El Salam
Human health is seriously threatened by fluoride poisoning worldwide. In this work, a number of metal-organic frameworks (M-MOFs; M = Chromium (Cr), Nickel (Ni), and Ni/Cr) were developed and evaluated as innovative adsorbents for the removal of fluoride from aqueous environments. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett –Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS) were used to characterize the materials. To understand the adsorption mechanism, thermodynamic parameters, isotherms, and adsorption kinetics were investigated. The Ni/Cr-MOF composite exhibited the maximum adsorption capacity (qm) 25.64 mg/g (97%) at the optimum conditions of pH 6.2, 0.15 g adsorbent dose, and 60 min contact time, demonstrating higher adsorption capacity than Cr-MOF 21.12 mg/g (89%) and Ni-MOF 17.07 mg/g (73%). The Langmuir isotherm and pseudo-second-order kinetic model were applied to describe the adsorption. The model reliability and parameter interactions were confirmed using statistical optimization. The validity of the model and the connection of important factors were validated by statistical optimization utilizing the central composite design (CCD) and analysis of variance (ANOVA). Ni/Cr-MOF maintained over 80% efficiency after four adsorption–desorption cycles, demonstrating its stability and reusability with minimal influence from coexisting anions during fluoride ion removal.