Fluoride adsorption on a cubical ceria nanoadsorbent: function of surface properties

Abstract

Fluoride adsorption onto a cubical ceria nanoadsorbent has been explored using batch as well as column studies, under various experimental conditions such as ionic strength, pH, surface loading, and the influence of major co-existing anions. High adsorption (Langmuir adsorption capacity; 80.64 mg g⁻¹) was attained at pH 7.0 within 2 h at an adsorbent dose of 1 g L⁻¹. Involvement of an inner-sphere complexation mechanism (ligand exchange mechanism) of fluoride adsorption has been confirmed by Fourier transform infrared spectroscopy (FTIR), O 1s X-ray photoelectron spectroscopy (XPS) and zeta potential (ζ) studies where, ligand exchange between the metal–hydroxyl (M–OH) groups and fluoride ions took place. X-ray powder diffraction (XRD) showed the amorphous nature of the developed nanoadsorbent, responsible for the high removal efficiency. The point of zero charge of the developed nanoadsorbent shifted from pH 6 to 5 after fluoride adsorption indicating the specific adsorption of fluoride. Real water analysis using fixed column adsorption indicated that the effectively treatable volume of water was ∼130-bed volume (BV) when the breakthrough point was set at 1.5 mg L⁻¹. The cost benefit analysis demonstrated the better economic viability of the developed cubical ceria nanoadsorbent for fluoride removal compared to other traditional adsorbents.