Transport of salty water through graphene bilayer in an electric field: A molecular dynamics study

Abstract

Molecular dynamics simulations are carried out to study the pressure-driven transport of salty (NaCl) water through the nanochannels formed by a graphene (GE) bilayer with and without a vertical electric field. The simulation results show that the channel thickness influences not only the velocity and numbers of water molecules and ions inside the channel, but also their responses to varied pressure and electric field intensity. The salt rejection rate is characterized by considering both the numbers of ions and water molecules inside the channel and their velocities. When the electric field is not imposed, the salt rejection rate varies slightly in the high-pressure range (50–300MPa), and is mainly affected by the channel thickness. When an electric field with high intensity (1–5V/Å) is imposed vertically under high driving pressure (300MPa), ions can be trapped inside the nanochannel. Simulations under lower electric field (0.01–0.1V/Å and 0.05–0.2V/Å) and pressure (5MPa and 10MPa) are also conducted. Under these circumstances, GE nanochannels can reject ions from entering the channel, indicating improved salt rejection rate and reduced ion channel accumulation.