Water-stable zirconium and iron-based metal-organic frameworks (MOFs) as fluoride scavengers in aqueous medium.

[Display omitted] • MIL-53 (Fe), UIO-66, acid promoted UIO-66, and MOF-235 synthesized hydrothermally. • Fluoride (F-) uptake preference for MOFs observed in the order of MIL-53 (Fe) > UIO-66 > AP-UIO-66 > MOF-235. • The optimal operating condition was explored by Box–Behnken design (BBD). • The q max of MIL-53 (Fe) for F- was 72.51 mg/g, more than many reported MOFs. Metal-organic frameworks (MOFs) of different water-stable classes were prepared hydrothermally and studied for fluoride (F-) capture in aqueous medium. In the screening test, the (F-) removal for MIL-53 (Fe), UIO-66, AP -UIO-66, and MOF-235 were 95.6%, 92.3%, 74.1% and 61.5%, respectively. MIL-53 (Fe) further explored by Box–Behnken design (BBD) approach to develop a mathematical model for the prediction of F- removal under determined environmental conditions. The model demonstrated that the mixing time was the most significant operational variable in the process. To maximize the F- capture, model optimization carried out and the best operational condition obtained as pH 4, mixing time of 60 min, and MIL-53 (Fe) dosage 0.25 g/L. Monolayer adsorption onto energetically equivalent sorption sites described the F- capture by MIL-53 (Fe). The qmax obtained by non-linear Langmuir model was 3.82 mmol F- per g MIL-53 (Fe). The sorption was favorable at the different F- concentrations in the range of 10–30 mg/L, based on the separation factor. Moreover, the kinetic models revealed that the rate of adsorption controlled by the migration of F- ions through the boundary layer. [ABSTRACT FROM AUTHOR]