A zwitterion metal-organic framework for the removal of fluoride from an aqueous solution

Excess fluoride is one of the water pollutants in the world, which is removed from water by chemical methods to produce sludge. On the other hand, techniques such as R.O. (Reverse Osmosis) also have problems with power consumption and wastewater disposal. Metal-organic frameworks are one of the newest adsorbents used to separate anions. In this study, MOF1 ({[Zn₃L₃(BPE)_1.5]·4.5DMF}_n) was used to remove fluoride from the aqueous solution. The influence of various factors such as pH, contact time, adsorbent amount, and temperature on fluoride uptake was investigated. Based on the results, the MOF synthesized in acidic media absorbs more fluoride ions. The reaction time in the first 20 min had a significant effect on fluoride removal, but its impact was significantly reduced in longer times. Increasing the adsorbent mass to reach saturation was adequate, but the ambient temperature of the water had no significant impact on the adsorption of fluoride ions. The results of kinetic studies confirm the pseudo-second-order kinetics of fluoride adsorption reactions in the presence of MOF1. Also, in this research, the central zinc metal has been used as a zwitterion to reduce the environmental effects of MOF.

Graphical abstract

Positive nitrogens on the surface of MOF1 pores are suitable sites for the adsorption of fluoride ions through electrostatic interactions, leading to the efficient removal of fluoride from the aqueous solution by this zwitterion metal-organic framework.