Charged nanoporous graphene membrane for enhancing reverse osmosis water desalination performance.

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