Fluoride removal by ordered and disordered mesoporous aluminas

Abstract

Highly ordered and disordered (MA-n) mesoporous aluminas with excellent fluoride adsorption performance have been successfully developed. The physicochemical and adsorption properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherms and fluoride removal experiments. Highly ordered mesoporous structure (OMA) was produced by using aluminum metal organic as precursor and wormlike disordered mesoporous structure (MA-n, MA-cl) was synthesized from inorganic aluminum salt precursors. The synthesized mesoporous alumina with a large pore size distribution of 7–14nm and large surface areas in the range of 163–338m2/g are beneficial for transport of solution in interconnected mesoporous channels and the fluoride ion was anchored on plenty of surface hydroxyl groups which provide high fluoride adsorption capacity and efficiency. Adsorption kinetics was described by pseudo-second-order, pseudo-first-order and intra-particle pore diffusion models, while, their adsorption equilibrium isotherms were described reasonably well by Langmuir model. Maximum fluoride adsorption capacities of OMA-400, OMA-850 and MA-n were 135, 91 and 95mg/g, respectively, which are higher than many reported alumina based adsorbents. Due to the ordered mesoporous structure which decreases the liquid transfer resistance, the OMA-400 showed extremely faster adsorption kinetics with a removal of 90% of F− within 20min at an optimal pH of 6. Presence of other anions like SO42−, NO3−, Cl− and HCO3− effect on fluoride removal efficiency and desorption study of OMA-400 and OMA-850 were also determined and compared.