Selective Molecular Sieving through a Large Graphene Nanopore with Surface Charges.

The precise control of the pore sizes at an atomic level has proved to be the biggest challenge of all for nanoporous graphene membranes for gas separation. Here, we propose a simple method to realize the selective molecular sieving through originally nonselective graphene nanopores by adding charges on the graphene surfaces. Molecular dynamic simulations show that the CO2/N2 selectivity of the graphene nanopore with a diameter of 0.52 nm increases up to 22.78 for a surface charge density of only -5.934 e/nm2. The selectivity improvement is related to the distinctive adsorption intensities of CO2 and N2 molecules on the charge-loaded graphene surfaces. This work points toward a promising road to tune the selectivity of graphene nanopores and therefore promotes the realization of porous graphene membranes and other two-dimensional porous membranes by accepting the pores with a wide size distribution and reducing the requirements in the control of pore sizes.