Rapid and extremely high adsorption performance of porous MgO nanostructures for fluoride removal from water

Fluoride is a non-metal that can often be found in groundwater posing a serious environmental health hazard worldwide. So, it is very important to remove excess fluoride from drinking water to maintain the optimal concentration of fluoride. To address this issue, the synthesis of porous MgO nanostructures has been reported herein through the sol-gel and hydrothermal methods to use them as an effective adsorbent for removal of fluoride from water. The as-synthesized MgO nanostructures are porous, highly crystalline, and pure as confirmed by microscopic and diffractometric analysis. N₂ gas adsorption-desorption study revealed that the BET surface areas of different MgO nanostructures are varied from 10.5 to 171 m² g^-1. The adsorption potential of MgO nanostructures is extremely high in the removal of fluoride from water with Langmuir adsorption capacity of 5716 to 15,691 mg g^-1 at 303 K. The kinetic studies revealed that nearly 90% of fluoride were removed within 5 min. The adsorption process is thermodynamically favorable and is exothermic in nature. A maximum Langmuir adsorption capacity of 29,131 mg g^–1 has been achieved at 313 K which is the highest for any adsorbent reported till now. The treatment of the experimental data with different isotherm and kinetic models suggests that these MgO nanostructures could be efficient, inexpensive, eco-friendly and convenient adsorbents for remediation of fluoride from water. The relative importance of test parameters such as the concentration of adsorbent, pH, and effect of co-existing ions on the adsorption performance of MgO nanostructures has been well investigated. The nanostructures are highly stable and are reusable up to the fifth cycle without losing too much of its adsorption performance.