Charged nanoporous graphene membranes for water desalination

Abstract

Water desalination using positively and negatively charged single-layer nanoporous graphene membranes are investigated using molecular dynamics (MD) simulations. Pressure-driven flows are induced by the motion of specular reflection boundaries with a constant speed, resulting in a prescribed volumetric flow rate. Simulations are performed for 14.40 Å hydraulic pore diameter membrane with four different electric charges distributed on the pore edges. Salt rejection efficiencies and the resulting pressure drops are compared with the previously obtained base-line case of 9.9 Å diameter pristine nanoporous graphene membrane, which exhibits 100% salt rejection with 35.02 MPa pressure drop at the same flow rate. Among the positively charged cases, q = 9e shows 100% and 98% rejection for Na⁺ and Cl⁻ ions respectively, with 35% lower pressure drop than the reference. For negatively charged pores, optimum rejection efficiencies of 94% and 93% are obtained for Na⁺ and Cl⁻ ions for the q = −6e case, which requires 60.6% less pressure drop than the reference. The results indicate the high potential of using charged nanoporous graphene membranes in reverse osmosis (RO) desalination systems with enhanced performance.