Performance and mechanism of hierarchically porous Ce–Zr oxide nanospheres encapsulated calcium alginate beads for fluoride removal from water

Abstract

Hierarchically porous Ce–Zr oxide nanosphere encapsulated calcium alginate millimeter-sized beads (CZ-CABs) were synthesized by using a sol–gel templating technique. Their defluoridation performance, including static and dynamic adsorption, was systematically evaluated. The adsorption kinetic followed the pseudo-second-order model. The adsorption isotherm could be divided into two distinct regions depending on the fluoride concentrations, and the CZ-CABs exhibited a Langmuir–Freundlich maximum fluoride adsorption capacity of 137.6 mg g⁻¹ under neutral conditions. Such a specific adsorption isotherm indicated that various mechanisms were involved in the fluoride adsorption depending on fluoride concentrations, which were further demonstrated by FTIR and XPS analyses. The effect of pH and co-existing anions on fluoride adsorption was studied. Furthermore, column adsorption experiments were conducted, and the results showed a high efficiency of the CZ-CABs for the removal of fluoride from water on a continuous flow basis.