Adsorption property of fluoride in water by metal organic framework: Optimization of the process by response surface methodology technique

Abstract

In this study, three types of adsorbents metal-organic frameworks were used to remove fluoride from wastewater. The influences of various parameters, such as initial fluoride concentration, pH, adsorption time, co-existing anions, and humic acid were also evaluated. The central composite design was used to optimize fluoride adsorption. Aluminum metal-organic frameworks (MIL-101(Al)), Ce(1,3,5-BTC)(H2O)6 metal-organic frameworks(Ce-BTC) and La(1,3,5-BTC)(H2O)6 metal-organic frameworks(La-BTC) were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) for surface area and total pore volume. The adsorption performance of MIL-101 (Al) was the best, Ce-BTC was the second, and La-BTC was the worst. The adsorption kinetic and isotherms models were studied. The results of the response surface methodology revealed that pH was the largest influencing factor in the removal of fluoride by Ce-BTC. When the initial solution pH is 3, the adsorbent dosage is 0.8 g/L, and the initial fluorine concentration is 40 mg/L, the fluorine removal efficiency is 96.8%, which was the local maximum. The adsorption data of MIL-101(Al), Ce-BTC and La-BTC were in keeping with Langmuir isotherm models and pseudo-second-order. Thermodynamic data showed that the adsorption process is endothermic and spontaneous, and the entropy increases during the adsorption of F− on MOFs.