A synergistic improvement of the molecular transport properties of a composite film is highly attractive for advances in the energy-efficient membranes. Herein, in the context of carbon capture, we demonstrate a remarkable enhancement in the CO2
selectivity by uniquely masking nanoporous single-layer graphene with polymer with intrinsic microporosity (PIM-1). In the process, we overcome a major bottleneck of the state-of-the-art pore-incorporation techniques in graphene where in addition to the molecular sieving nanopores, larger nonselective nanopores are also incorporated, which so far, has restricted the realization of CO2
-sieving from the single-layer graphene membranes.[1-2] By masking nanoporous graphene (NG) with PIM-1, the direct gas-phase transport from the larger nanopores is eliminated, benefitting the transport of CO2
. Overall, we achieve much higher CO2
selectivity (33) from the composite film than that from the standalone NG (10) and the PIM-1 membranes (15), and high CO2
permeance up to 2500 GPU. The selectivity enhancement is explained by an analytical gas transport model for nanoporous graphene, which shows that the transport of the stronger-adsorbing CO2
is dominated by the adsorbed phase transport pathway whereas the transport of N2
benefits significantly from the direct gas-phase transport pathway. Further, slow positron annihilation Doppler broadening spectroscopy reveals that the interactions with graphene reduce the free volume of interfacial PIM-1 chains which is expected to contribute to the selectivity. Masking of graphene with nanoporous polymer is doubly attractive because the polymer film also acts as the mechanical reinforcement for graphene, enabling the fabrication of graphene membranes without cracks.
 He, G., Huang, S., Villalobos, L.F., Zhao, J., Mensi, M., Oveisi, E., Rezaei, M. and Agrawal, K.V.* High-Permeance polymer-Functionalized single-Layer graphene membranes that surpass the postcombustion carbon capture target. Energy & Environmental Science 2019, 12(11), 3305-3312.
 Zhao, J., He, G., Huang, S., Villalobos, L.F., Dakhchoune, M., Bassas, H. and Agrawal, K.V.* Etching gas-sieving nanopores in single-layer graphene with an angstrom precision for high-performance gas mixture separation. Science advances 2019, 5, eaav1851.
 Huang, S., Dakhchoune, M., Luo, W., Oveisi, E., He, G., Rezaei, M., Zhao, J., Alexander, D.T., Züttel, A., Strano, M.S. and Agrawal, K.V.* Single-layer graphene membranes by crack-free transfer for gas mixture separation. Nature communications 2018, 9(1), 1-11.