Tuning Pore Size in Porous Graphene Membrane for O₂/N₂ Separation

Graphene with angstrom-scale, zero-dimensional pores offers a promising platform for gas separations due to its exceptional permeance and potential for molecular sieving. Herein, we demonstrate a dynamic strategy to tune N-functionalized graphene pores, achieving selective oxygen (O₂) separation from nitrogen (N₂), a particularly challenging separation due to their similar kinetic diameters. We exploit the heterogeneity of functional groups at the pore edge to tune the pore limiting diameter (PLD). By facile thermal annealing, we convert primary amine groups at the pore edge to lattice-incorporated nitrogen. Temperature-dependent extent of conversion allows to tune the steric hindrance from amine-CO₂ complex, and therefore, PLD for O₂/N₂ separation in favor of O₂ permeation. The resulting membranes exhibit attractive O₂/N₂ separation performance, with O₂ permeance near 2500 GPU with O₂/N₂ selectivity above 10, significantly outperforming the state-of-the-art membranes. This is attractive for energy-efficient and modular production of O₂ from air and can cut down fuel consumption in natural gas-fired furnaces in the chemical industry by 60%.