Multiwalled CNTs for Cr(VI) removal from industrial wastewater: An advanced study on adsorption, kinetics, thermodynamics for the comparison between the embedded and non-embedded carboxyl group

Abstract

The adsorption capabilities of multiwalled carbon nanotubes (MWCNTs) with and without the embedded carboxyl group for the removal of parts per million levels of hexavalent chromium were examined as a function of several parameters, namely contact time, pH of initial solution, initial concentration of Cr(VI), adsorbent dosage as well as temperature of solution. Adsorption isotherms have been utilized to explain the adsorption mechanism. Ion exchange, intra-particle diffusion, and electrostatic interactions are found to be the fundamental mechanisms describing the adsorption of Cr(VI). The maximum adsorption capacities of Cr(VI) ion by raw MWCNTs and functionalized MWCNTs were found to be 84.75 and 78.13 mg · g−1, respectively, as calculated by the Langmuir adsorption isotherm model. This is with regard to the electron-rich atoms inside the functional group which repels the negatively charged dichromate ions. Kinetic studies were performed, and the data was found in good agreement with the pseudo-second-order. © 2020 Canadian Society for Chemical Engineering