Molecular insight into CO2/N2 separation using a 2D-COF supported ionic liquid membrane

Abstract

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 CO₂/N₂ separation. The separation performance was investigated using molecular dynamics simulation. There was an ultrahigh CO₂ permeability up to 2.317 × 10⁶ GPU, and a better CO₂ selectivity was obtained when compared to that of N₂. 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 N₂, as well as a gating effect, which allows CO₂ passage and inhibits N₂ passage, contribute to the better CO₂ selectivity over N₂. 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.