The framework flexibility of metal–organic frameworks (MOFs) is beneficial for gas storage and adsorption but is disadvantageous to the separation process based on the size-extrusion mechanism. Herein, the framework flexibility of ZIF-7, a typical MOF famous for its phase transition between wide-pore (ZIF-7-I) and narrow-pore (ZIF-7-II) forms on desolvation, was successfully hindered by embedding MOF nanocrystals in the rigid polymer matrix. For the first time, it was experimentally demonstrated that ZIF-7 could be “locked” in the wide-pore phase (ZIF-7-I) even after complete desolvation. A mixed-matrix membrane containing ZIF-7-I nanocrystals and rigid polyimides showed O₂ permeability of 3 Barrer and O₂/N₂ selectivity of 15, surpassing the state-of-the-art upper limit for O₂/N₂ and falling in the commercially attractive region. In view of the weak competitive interaction between O₂/N₂ and hybrid membrane materials, similar permeation results were also found for the separation of equal-molar O₂/N₂ binary mixtures.

中文翻译：

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锁定MOF ZIF-7中的相变：改善混合基质膜中O ₂ / N ₂分离的选择性†

金属有机框架（MOF）的框架灵活性有利于气体的存储和吸附，但不利于基于尺寸挤压机理的分离过程。在本文中，嵌入MOF成功地阻止了ZIF-7的骨架柔韧性，ZIF-7是典型的MOF，在去溶剂化过程中其在宽孔（ZIF-7-I）和窄孔（ZIF-7-II）形态之间发生相变而闻名刚性聚合物基质中的纳米晶体。首次通过实验证明，即使完全脱溶剂后，ZIF-7仍可“锁定”在宽孔相（ZIF-7-I）中。包含ZIF-7-I纳米晶体和刚性聚酰亚胺的混合基质膜的O ₂渗透率为3 Barrer和O ₂ / N ₂15的选择性超过O ₂ / N ₂的最新上限，并落入商业吸引力区域。鉴于O ₂ / N ₂与杂化膜材料之间的竞争性较弱，对于等摩尔O ₂ / N ₂二元混合物的分离也发现了类似的渗透结果。