Molecular insight into CO 2 /N 2 separation using a 2D-COF supported ionic liquid membrane.

The covalent organic framework (COF) shows great potential for use in gas separation because of its uniform and high-density sub-nanometer sized pores. However, most of the COF pore sizes are large, and there are mismatches with the gas pairs (3-6 Å), and the steric hindrance cannot work in gas selectivity. In this work, one type of COF (NUS-2) supported ionic liquid membrane (COF-SILM) was prepared for use in CO 2 /N 2 separation. The separation performance was investigated using molecular dynamics simulation. There was an ultrahigh CO 2 permeability up to 2.317 × 10 6 GPU, and a better CO 2 selectivity was obtained when compared to that of N 2 . The physical mechanism of ultrahigh permeability and CO 2 selectivity are discussed in detail. The ultrathin membrane, high-density pores and high transmembrane driving force are responsible for the ultrahigh permeability of CO 2 . The different adsorption capabilities of ionic liquid (IL) for CO 2 and N 2 , as well as a gating effect, which allows CO 2 passage and inhibits N 2 passage, contribute to the better CO 2 selectivity over N 2 . Moreover, the effects of the COF layer number and IL thickness on gas separation performance are also discussed. This work provides a molecular level understanding of the gas separation mechanism of COF-SILM, and the simulation results show one potential outstanding CO 2 separation membrane for future applications.