One pot green synthetic route for the preparation of cetyl trimethyl ammonium bromide grafted multiwalled carbon nanotubes and their application towards defluoridation

Abstract

In this study we have synthesized cetyl trimethyl ammonium bromide (CTAB) grafted multiwalled carbon nanotubes (CGCNTs) and evaluated their potential towards the removal of fluoride ions from aqueous solutions. The grafting was done by ultrasonication using a relatively green solvent (isoamyl alcohol) medium. The mechanism of adsorption of the fluoride ions by the CGCNTs could be attributed to electrostatic attractions followed by ion exchange. The adsorbent features are ably supported by various physico-chemical characterization techniques and the effect of various analytical parameters affecting the adsorption is examined in detail. Moreover, this nano adsorbent performed well over a considerably wide pH range of 2.0–11.0. The experimental data obtained from the adsorption studies were analyzed by the Langmuir and Freundlich equation using a linearized correlation coefficient at room temperature. The adsorption kinetics could be modelled by a pseudo-second-order rate expression. The maximum uptakes of fluoride by the CGCNTs and oxidized CNTs were found to be 20.1 and 11.1 mg g⁻¹, respectively. The effect of the presence of other anions like sulfate, phosphate, nitrate and chloride on fluoride removal efficiency by the prepared CGCNTs was also tested. The study of thermodynamic parameters that affect the sorption process indicated the spontaneity and exothermic nature of adsorption. The recyclability of the adsorbent for five cycles and the application to fluoride spiked ground water has also been demonstrated.