A Molecular Dynamics Study of Aqueous Na+/Mg2+ Intercalation Behavior in Vanadium Oxide Nanopores.

Selective removal of Mg2+ from seawater is essential to mitigate reverse osmosis membrane scaling yet remains difficult because abundant and mobile Na+ competes for uptake. Low-cost layered electrochemical materials such as vanadium oxide (V2O5) offer tunable confinement for ion insertion, making them attractive candidates for targeting Mg2+ in saline feeds. Here, we parametrize an intermolecular potential model for V2O5 and employ molecular dynamics simulations to examine Na+/Mg2+ intercalation from bulk brine solutions into slit-shaped V2O5 pores as a function of brine composition, pore size (d001), and temperature. We identify a sharp confinement-induced divergence at d001 < 12 Å where Mg2+ has a stronger intrinsic thermodynamic affinity over Na+. However, under seawater-like conditions, the high concentration of Na+ and the slower entry of Mg2+ into the pores limit the extent to which this thermodynamic preference translates into practical Mg2+ selectivity. Further exploration of its performance (e.g., the role of applied electric fields) could help quantify the underlying thermodynamic and kinetic separation properties of these materials.