Covalent organic frameworks-confined ionic liquids membranes lead to high-efficient CO2/N2 separation

YM Liu and YD Guo and ZL Wang and YH Kong and YW Liu and XC Zhang, SEPARATION AND PURIFICATION TECHNOLOGY, 368, 132933 (2025).

DOI: 10.1016/j.seppur.2025.132933

Covalent organic frameworks (COFs) are promising materials for gas separation due to their excellent stability and tunable structure. However, their inherently large pore sizes often limit their application in the separation of small gas molecules, such as CO2 and N-2. In this study, we regulate the pore size by confining imidazolium-based ionic liquids (ILs) within the TpPa-1 COF using molecular dynamic simulation. A systematic investigation was conducted to explore the effects of IL loading and anion type on the CO2/N-2 separation. It was found that high IL loading effectively reduces the COF pore size and enhances the dispersion of ILs within COF, resulting in a stratified IL structure, where cations primarily occupy the corners and centers of the COF pores, while anions are staggered near the cations. Due to differences in interactions, CO2 is adsorbed near the COF pore walls, while N-2 is dispersed in the ILs, which promotes faster diffusion of N-2 compared to CO2. The size and shape of anions influence their distribution, as well as the interaction and transport of gases. Among the ILs considered, the BmimBF4/COF membrane is identified as the optimal candidate for CO2/N-2 separation.

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