Ionic liquid gated 2D-CAP membrane for highly efficient CO2/N2 and CO2/CH4 separation

Abstract Recently, a two-dimensional conjugated aromatic polymer (2D-CAP) membrane has been synthesized, and it shows promising applications in the selected gas separation. However, the sub-nanometer pores of the 2D-CAP membrane are relatively large compared with small gas molecules like CO2, N2, and CH4, which impedes the efficiency of the gas separation. Here, we report a strategy to improve the gas separation performance of 2D-CAP membranes. Specifically, coating ultra-thin ionic liquid (IL) onto the 2D-CAP membrane was found to well harmonize the pore size of 2D-CAP membranes. In this work, the gas separation performance of this 2D-CAP supported IL membrane (2D-CAP SILM) was investigated using molecular dynamics simulations. An ultrahigh CO2 permeance of ~105 GPU, which is larger than many reported theoretically predicted results, was exhibited. Meanwhile, an excellent selectivity of CO2/N2 and CO2/CH4 beyond 40 was obtained. The ultrathin membrane and the high-density pore are responsible for the high gas permeance, and the selectivity could be ascribed to IL adsorption selectivity of CO2 over N2/CH4 and a fascinating gating effect that anion of IL ([BF4]−) suspending upside the pore center allows CO2 passage while prohibits N2/CH4 passage. The present work suggests a promising membrane for practical highly efficient CO2 separation.