Abstract Cage-type MOFs based Mixed-matrix membranes (MMMs) hardly exhibit screening effect of gas molecules due to the flexible aperture. Regulation of nanocages of MOFs by Ionic Liquid (IL) has been proved to be effective. Therefore, in this work, an IL adsorption/infiltration two-step strategy is proposed to confine IL into the nanocages of MOFs, achieving fine tuning of effective cage size for screening gas pair with similar size. [Bmim][PF6] are first adsorbed on the outer-surface of ZIF-8, then through heat treatment, the aperture of ZIF-8 is dilated, and the bigger [Bmim][PF6] molecules infiltrate through the dilated aperture into the nanocage driven by thermodynamics and differential concentration. When the temperature is down to room temperature, the aperture is narrowed to 3.4 A, thus [Bmim][PF6] are confined into nanocages, which are confirmed by PXRD, TGA and FT-IR characteristics. By controlling IL content in the cage, the effective cage size of ZIF-8 is tuned to specific slope among dynamic diameters of CO2 over N2, which is perfectly reflected in the CO2/N2 separation. Compared with ZIF-8/Pebax MMMs, the IL@ZIF-8/Pebax MMMs exhibit improved CO2/N2 selectivity but decreased CO2 permeability, demonstrating effectiveness of cage size adjustment. Furthermore, with the IL molecules inside ZIF-8 cage increasing, the CO2/N2 selectivity of the MMMs continues to rise, indicating cage size screening effect of ZIF-8 by IL infiltration. Especially, the IL8@ZIF-8/Pebax MMMs exhibit the best gas separation performances with CO2 permeability of 117 Barrer and CO2/N2 selectivity of 84.5, beyond the 2008 Robinson upper bound. The proposed strategy provides an effective but facile way to confine IL into the cages of MOFs to precisely screen gas pairs with similar size and can be easily expanded to other IL and MOFs system.

中文翻译：

---

离子液体通过两步吸附/渗透策略调节 MOF 的纳米笼尺寸，以增强混合基质膜的气体筛选

摘要 基于笼型MOFs的混合基质膜（MMMs）由于孔径灵活，几乎不表现出气体分子的屏蔽作用。离子液体 (IL) 对 MOF 纳米笼的调节已被证明是有效的。因此，在这项工作中，提出了一种离子液体吸附/渗透两步策略，将离子液体限制在 MOF 的纳米笼中，实现有效笼尺寸的微调，以筛选具有相似尺寸的气体对。[Bmim][PF6]首先吸附在ZIF-8的外表面，然后通过热处理，ZIF-8的孔径扩大，较大的[Bmim][PF6]分子通过扩大的孔径渗入到由热力学和差异浓度驱动的纳米笼。当温度降至室温时，孔径缩小至 3.4 A，因此 [Bmim][PF6] 被限制在纳米笼中，经 PXRD、TGA 和 FT-IR 特性证实。通过控制笼中的 IL 含量，ZIF-8 的有效笼尺寸被调整为 CO2 与 N2 动态直径之间的特定斜率，这完美地反映在 CO2/N2 分离中。与 ZIF-8/Pebax MMM 相比，IL@ZIF-8/Pebax MMM 表现出更高的 CO2/N2 选择性但降低了 CO2 渗透性，证明了笼子尺寸调整的有效性。此外，随着 ZIF-8 笼内 IL 分子的增加，MMMs 的 CO2/N2 选择性继续上升，表明 ZIF-8 对 IL 渗透的笼大小筛选效应。特别是 IL8@ZIF-8/Pebax MMMs 表现出最好的气体分离性能，CO2 渗透率为 117 Barrer，CO2/N2 选择性为 84.5，超过了 2008 年 Robinson 的上限。