Removal of fluoride from aqueous solution by porous Vaterite calcium carbonate nanoparticles

Abstract

This study is based on a simple, low-cost and a novel approach towards the removal of excess fluoride ions from aqueous solution by absorbing fluoride on porous vaterite calcium carbonate nanoparticles (PVCCNPs) synthesised using ethylene glycol-water soft template method. SEM images clearly show the porous nature of aggregated nanoparticles present in the dry powder. Physicochemical properties of synthesised PVCCNP and fluoride on PVCCNP was characterised further by FTIR, XRD, XRF, EDX, and TGA-DTG. Fluoride removal by PVCCNPs from 100.00 ml of 10.0 mg l−1 NaF solution with 0.500 g of PVCCNPs, determined using a fluoride ion-selective electrode, indicates that around 90% removal is achieved within 1 h thus reducing the level to desired 1 ppm. The pseudo-second order kinetic model has a better fit to describe the adsorption of fluoride on PVCCNP than pseudo-first order model. The Langmuir isotherm model is more appropriate to describe the equilibrium behaviour of the adsorption process, than the Freundlich model. Given that the value of n (Freundlich constant) is greater than 1 (3.07) and RL value is in the range of 0 < RL <1 (0.014–0.024) implies that the adsorption process is spontaneous and fluoride ions are favourably adsorbed on PVCCNPs. Langmuir model shows that the maximum adsorption capacity of fluoride is 1.956 mg g−1. Excess fluoride in drinking waters causes several severe ill-health effects and filter media based on these nanoparticles can be used to remove fluoride down to safe and required levels to tackle these health problems. As such, PVCCNPs-based filter can be designed to remove fluoride in drinking waters. This may be a way for controlling fluorosis and many other diseases associated with excess fluoride present in drinking waters.