ATOMIC BOUNDARY POSITION AND STERIC EFFECTS ON ION TRANSPORT AND SEPARATION THROUGH NANO POROUS GRAPHENE MEMBRANE

Abstract

The electrostatic attraction between ion and water is the primary concern of changing the ion's bare diameter. The modification in ion shape is known as the steric effect that plays a crucial role in the desalination approaches using nanoporous graphene membranes. Utilizing molecular dynamics (MD), a pressure-driven flow is generated using specular reflection wall movement at a constant speed to analyze the saltwater transport through a nanoporous graphene membrane. This study signifies pore diameter's atomic boundary position impact on single-ion transportation and the steric influence of ions on the water mass flow rate and velocity profile. Due to the Columbic interaction between ions and water, ions hinder the water molecules from their regular velocity, which also lessens the flow rate of water molecules. For the different atomic boundary positions of pore diameter, we propose the ratio of the input energy of the total ion and the energy barrier of ion dehydration as the theoretical ion transportation. Interestingly, a significant deviation for different atomic boundary positions is observed for ion rejection at less than 1 nm pore diameter. The ion rejection drops considerably if all hydration layers break off due to high critical pressure. However, at more than 1nm pore diameter, the ion rejection closely matches the atomic boundary position specified to the 2% water density drop inside the nanopore.