Atomic boundary position and steric effects on ion transport and separation through nanoporous graphene membrane

Abstract

The electrostatic attraction between ions and water is the primary reason for the change in ion bare diameter, which plays a crucial role in saltwater transportation. This study utilizes molecular dynamics (MD) to analyze saltwater transport through a nanoporous graphene membrane by pressure-driven flow. In this work, we describe the impact of pore diameter atomic boundary position on single-ion transportation and signify the steric effect of ions on the water mass flow rate and velocity profile. Due to hydration layer formation, ions hinder the water molecules from their regular velocity, which also decreases the flow rate of water molecules. Interestingly, a significant deviation for different atomic boundary positions is observed for ion rejection for pore diameters less than 1 nm. However, for larger pore diameters, the ion rejection closely matches the atomic boundary position specified by a 2 % water density drop inside the nanopore.