Molecular Dynamics Study of Mg²⁺/Li⁺ Separation via Biomimetic Graphene-Based Nanopores: The Role of Dehydration in Second Shell

Abstract

Residual Mg reduces the performance of lithium-ion batteries. However, separating Mg and Li is difficult because of their similar ionic properties. Inspired by the high selectivity of biological Mg channels, this work utilizes atomistic simulations to investigate the ability of graphene-based nanopores with diameters of 0.789, 1.024, and 1.501 nm to separate Mg and Li under a series of transmembrane voltages. We analyzed the spatial distribution of molecules in the nanopores' vicinity, structure properties of ionic hydration, and potential of mean force of ions traveling through the nanopores. Separation was mainly caused by the difference in dehydration between the second hydration shells of Mg and Li. When ions traveled through nanopores, Li had to overcome a greater energy barrier than Mg because it had to shed more water molecules and break more hydrogen bonds in the second hydration shell compared with Mg. Moreover, the ionic Coulomb blockade of Mg occurred near the pore mouth, impeding Li transport and increasing selectivity when the pore diameter decreased to subnanometer.

Engineering Leaf-Like UiO-66-SO3H Membranes for Selective Transport of Cations

“…However, the permeation of Mg 2+ increases drastically, especially in K + /Mg 2+ and Li + /Mg 2+ , which leads to the significant decrease in selectivity. It is deduced that the ion–ion interaction, ion–water interaction, or wall–ion interaction would affect the ions transfer, which has been confirmed in previous research works [ 40 – 42 ]. However, the specific reason in our case is still unclear and needs more investigation.…”

Chitosan-covered liposomes as a promising drug transporter: nanoscale investigations

“…The calculated D c for Cl À ions in the chitosan branched polyelectrolyte, conned between two adjacent liposomes, is of the order of 10 À6 cm 2 s À1 , these values are in good agreement with the experimental measurements of diffusion coefficients in aqueous solutions, 89 and are in accord with the calculated values from recently published works using all-atom MD simulations. 90 We note that the ballistic regime is not observed for all constituents, this can be explained by the fact that the simulated system is previously equilibrated in the NPT-NPH MD simulation.…”

Origin and control of ionic hydration patterns in nanopores

“…We compare the analytically predicted patterns with the results of MD simulations for different ionic locations near graphene nanopores with a diversity of shapes, geometries and strains. The results are applicable to narrow biological channels [24,38,39], functionalized sub-nanopores [24,25,40,41], nanotubes [42] and nanoslits [16,34]. Thus, this work takes an important step towards controlling the function of nanoscale devices by tailoring the hydration patterns.…”