Adsorptive, kinetics and regeneration studies of fluoride removal from water using zirconium-based metal organic frameworks

Fluoride contamination has been recognised as one of the major problems worldwide, imposing a serious threat to human health and affecting the safety of drinking water. Adsorption is one of the widely considered appropriate technologies for water defluorination. The present study describes the preparation of a zirconium-based metal organic framework (MOF-801) adsorbent using a solvothermal method and its adsorption efficiency for removal of fluoride ions from water. The morphology of MOF-801 was characterized by PXRD, FESEM and XPS, and the pore structure and surface area were calculated according to BET. It was found that the synthesized MOF-801 showed the distinguishable octahedral shape particle with a lattice spacing of 0.304 nm, indicative of (011) planes of ZrO₂. Adsorption studies were carried out to study the defluorination effectiveness by varying contact time (30-150 min), adsorbent dose (0.3-1.5 g L^-1), adsorbate concentration (5-25 mg L^-1), as well as kinetics and isotherms. The maximum removal efficiency for fluoride using MOF-801 at equilibrium was found to be 92.3%. Moreover, the adsorption kinetic studies indicate that the overall fluoride adsorption process was best described by pseudo-second-order kinetics. The adsorption data were well-fitted with the Langmuir isotherm model (<i>R</i> ² = 0.9925) with maximum adsorption capacity of 19.42 mg g^-1. The synthesized MOF-801 had good reusability and was used in up to four cycles for fluoride removal attaining around 79% removal efficiency after the fourth cycle. All the results suggested that the synthesized MOF-801 has potential to be an excellent adsorbent for wastewater defluorination treatment.