Molecular insight into CO2/N2 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 angstrom), 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 CO2/N-2 separation. The separation performance was investigated using molecular dynamics simulation. There was an ultrahigh CO2 permeability up to 2.317 x 10(6) GPU, and a better CO2 selectivity was obtained when compared to that of N-2. The physical mechanism of ultrahigh permeability and CO2 selectivity are discussed in detail. The ultrathin membrane, high-density pores and high transmembrane driving force are responsible for the ultrahigh permeability of CO2. The different adsorption capabilities of ionic liquid (IL) for CO2 and N-2, as well as a gating effect, which allows CO2 passage and inhibits N-2 passage, contribute to the better CO2 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 CO2 separation membrane for future applications.