Selectivity trend of gas separation through nanoporous graphene

By means of molecular dynamics (MD) simulations, we demonstrate that porous graphene can efficiently separate gases according to their molecular sizes. The flux sequence from the classical MD simulation is H₂>CO₂≫N₂>Ar>CH₄, which generally follows the trend in the kinetic diameters. This trend is also confirmed from the fluxes based on the computed free energy barriers for gas permeation using the umbrella sampling method and kinetic theory of gases. Both brute-force MD simulations and free-energy calculations lead to the flux trend consistent with experiments. Case studies of two compositions of CO₂/N₂ mixtures further demonstrate the separation capability of nanoporous graphene.