Enhancing the CO2/CH4 gas separation performance of graphene membranes via oxygen functionalization

Membrane separation has emerged as a promising and environmentally friendly technique providing high selectivity and permeability. Graphene could be an extremely highly permeable gas separation membrane; however, its implementation and separation ability require further improvement. Herein, we describe the optimization of a graphene membrane for CO 2 /CH 4 gas separation using molecular dynamics (MD) simulations. The MD simulations indicate that among the evaluated membranes, only that with pores of 0.41 nm in diameter exhibits sufficient separation ability. However, as the graphene pore size and distribution are experimentally difficult to control, we need to investigate the other controllable parameter, except for the graphene pore size. The experimental separation test indicates that graphene membranes achieve a CO 2 /CH 4 selectivity greater than one without strict control of the pore size. We assume that the high selectivity is due to the oxygen-functional groups on graphene. MD simulations performed for the graphene with oxygen functional groups then indicate that oxygen functionalization enhances the separation and permeance abilities of graphene. Subsequently, partial oxidation of graphene by O 2 plasma treatment is also experimentally demonstrated to increase the CO 2 /CH 4 selectivity of the graphene membrane while maintaining the CO 2 permeance. Therefore, this study demonstrates that oxygen functionalization enhances the separation performance of graphene-based membranes.