Mg-Channel-Inspired Nanopores for Mg/Li Separation: The Effect of Coordination on the Ionic Hydration Microstructures.

The separation behaviors of Mg and Li were investigated using molecular dynamics. Two functionalized graphene nanopore models (i.e., co_5 and coo_5) inspired by the characteristic structural features of Mg channels were used. Both nanopores exhibited a higher preference to Mg than to Li, and the selectivity ratios were higher for coo_5 than for co_5 under all the studied transmembrane voltages. An evaluation of the effect of coordination on the ionic hydration microstructures for both nanopores showed that the positioning of the modified groups could better fit a hydrated Mg than a hydrated Li, as if Mg was not dehydrated according to hydrogen bond analysis of the ionic hydration shells. This condition led to a lower resistance for Mg than for Li when traveling through the nanopores. Moreover, a distinct increase in hydrogen bonds occurred with coo_5 compared with co_5 for hydrated Li, which made it more difficult for Li to pass through coo_5. Thus, a higher Mg/Li selectivity was found in for coo_5 than for co_5. These findings provide some design principles for developing artificial Mg channels, which have potential applications as Mg sensors and novel devices for Mg/Li separation.