Cross-scale synergy: Highly selective CO2/N2 separation via mixed-matrix membranes based on β-cyclodextrin porous liquids

Mixed matrix membranes (MMMs) offer a promising route to high-performance gas separation by integrating the benefits of fillers and polymer matrices. However, Polymers of Intrinsic Microporosity (PIM-1) suffers from poor interfacial compatibility with fillers and is constrained by the Robeson upper bound. As a result, the selectivity of MMMs remains less than ideal. This study proposes a cross-scale coordination strategy that adjusts the molar ratio of β -cyclodextrin ( β -CD) to the oligomer KH560-M2070 during the synthesis of porous liquids (PLs). This cross-scale coordination boosts MMM performance at both macro and micro levels. Grafting more oligomers increases the porous liquid's fluidity at the macroscopic scale. This effect arises from fewer hydrophilic hydroxyl groups on β -CD and the “like dissolves like” nature of the oligomers. As a result, the filler loading increases from 2 wt% to 10 wt%. KH560-M2070 and β -CD are covalently linked at both ends, creating a graded pore structure (0.41–0.8 nm) at the microscopic level. Our experimental data show that the β -CD PLs (1:0.7)/PIM-1 MMM achieves a CO 2 /N 2 selectivity of 65.68 ± 2.16 at 30 °C, well above the 2019 Robeson upper bound. This cross-scale strategy thus offers a new route for applying porous liquids in gas separation.