Adsorption of fluoride over a metal organic framework Uio-66 functionalized with amine groups and optimization with response surface methodology

Abstract

In this study, a new adsorbent called metal organic framework was used for the removal of fluoride from aqueous solutions. Effects of various parameters such as pH, fluoride initial concentration, contact time, adsorbent dose, and co-existing anions were also evaluated. The central composite design was used to optimize the fluoride adsorption. The Uio-66-amine was characterized by x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) spectra, field emission scanning electron microscopy (FE-SEM), energy dispersive x-ray spectroscopy (EDAX) and Brunauer-Emmett-Teller (BET) surface area and total pore volumes. The isotherm and kinetics models were investigated. The central composite design results showed that pH was the most influential factor in the removal of fluoride with Uio-66-amine. With the increase of fluoride concentration, fluoride adsorption was decreased. The results show that the best local maximum was found to be at the initial solution pH of 7, initial ion concentration of 12.18mg/L, adsorbent dose of 0.4g, contact time of 32.4min, fluoride removal efficiency of 88.14%, and desirability of 1. The maximum adsorption of fluoride was 41.5mg/L and adsorption data of Uio-66-amine fit well with the pseudo-second order and Langmuir isotherm models.