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.

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With the rapid development of a two-dimensional (2D) nanomaterial, the confined liquid binary mixture has attracted increasing attention, which has significant potential in membrane separation. Alcohol/water is one of the most common systems in liquid-liquid separation. As one of the most focused systems, recent studies have found that ethanol molecules were preferentially adsorbed on the inner surface of the pore wall and formed an adsorbed ethanol layer under 2D nanoconfinement. To evaluate the effect of the alcohol adsorption layer on the mobility of water molecules, molecular simulations were performed to investigate four types of alcohol/water binary mixtures confined under a 20 Å graphene slit. Residence times of the water molecules covering the alcohol layer were in the order of methanol/water < ethanol/water < 1-propanol/water < 1-butanol/water. Detailed microstructural analysis of the hydrogen bonding (H-bond) network elucidated the underlying mechanism on the molecular scale in which a small average number of H-bonds between the preferentially adsorbed alcohol molecules and the surrounding water molecules could induce a small degree of damage to the H-bond network of the water molecules covering the alcohol layer, resulting in the long residence time of the water molecules.