Molecular dynamics simulation of the adsorption of alkali metal cations on carbon nanotubes surfaces

Abstract

In a previous work, we prepared multiwalled carbon nanotubes (MWCNTs) impregnated with alkali metals and when characterized by different techniques, we observed that the incorporation of Cs to the MWCNTs by impregnation with Cs acetate was produced to a lesser extent than for the rest of alkali metal (Li, Na and K) acetates. In order to explain these results, in this paper we present classical molecular dynamics (MD) simulations of alkali metal cation (Li+, Na+, K+ and Cs+) adsorption on the surface of a (6,6) CNT functionalized with carboxylate groups. We study the time evolution of the distance between the alkali cations and the CNT surface, the oxygen-cation radial distribution functions, the structure of the first hydration shell, the diffusion coefficient of the cations and the interaction energies with the CNT. We conclude that the high mobility of the Cs+ cation as well as the small electrostatic interaction with the functional groups of the CNT surface could explain its lesser adsorption, when compared with the other three alkali metal cations, agreeing with the results of the lower incorporation of Cs to the MWCNTs observed by the different characterization techniques.