Adsorption Capacity and Selectivity of Bicontinuous Nanoporous Graphene for CO ₂ /N ₂ Separation

Molecular dynamics simulations using the ReaxFF reactive force field were conducted to investigate the adsorption capacity and selectivity of bicontinuous nanoporous graphene (BNG) for CO2 and N2 at 300 K. Pure-component adsorption was studied at pressures from 1 to 5 atm, and CO2/N2 selectivity was investigated for binary mixtures at 1 atm total pressure. The adsorption capacity increases monotonically with pressure, reaching 17.7 mmol g–1 for CO2. BNG exhibits a clear preference for CO2 over N2, with selectivity increasing from 2.9 to 4.5 as the CO2 concentration rises from 20% to 50%. Local composition profiles reveal that the most favorable physisorption sites are located between 3 and 4 Å from the graphene surface, with a peak CO2 occupancy near 3.25 Å. The accumulation of CO2 in these interfacial regions enhances system stabilization and lowers the total energy during adsorption. These findings provide molecular-level insight into the adsorption and separation mechanisms of CO2/N2 mixtures in BNG and underscore its potential as a selective, stable, and efficient physisorbent for postcombustion CO2 capture.