Synergistic lewis acid-base dual sites in porous organic framework-based MMMs toward superior CO2 separation

Porous organic frameworks (POFs) have garnered significant attention as potential filler materials for gas separation applications. Nevertheless, most available POFs predominantly possess a single type of adsorption site, which limits their overall performance. In this study, two ferrocene-based POFs, termed FcDA POF-1 and FcAc POF-2, were synthesized using ferrocene derivatives and pyrrole as monomeric precursors. The resulting POFs exhibited dual Lewis acid-base sites and high specific surface area. Extensive characterization validated excellent interfacial compatibility when these POF fillers were incorporated into 6FDA-DAM polymer matrix. The optimized mixed-matrix membrane (MMMs) based on FcDA POF-1 achieved exceptional CO 2 permeability of 3278.1 Barrer, coupled with an ideal CO 2 /N 2 selectivity of 58.4. These metrics represent enhancements of 260% and 208%, respectively, compared to the pristine 6FDA-DAM membrane, notably exceeding the 2019 Robeson upper bound. Density functional theory (DFT) calculations supported the hypothesis that multiple weak interactions between CO 2 molecules and FcDA POF-1, occurring at the electron-rich nitrogen atoms (Lewis base sites) and electron-deficient cyclopentadienyl groups (Lewis acid sites), synergistically enhance selective CO 2 recognition. Further evaluations under mixed-gas conditions, varying pressures and temperatures, as well as long-term stability tests, substantiated the membranes’ practical applicability. This work underscores rational design principles for constructing high-performance MMMs and presents a viable avenue for efficient CO 2 separation.