Cage-Interconnected Metal–Organic Framework with Tailored Apertures for Efficient C2H6/C2H4 Separation under Humid Conditions

Metal–organic frameworks (MOFs) with open metal sites (OMSs) have been shown to preferentially adsorb unsaturated hydrocarbons such as C2H4 due to the formation of π-complexation. However, the adsorption capacity and selectivity might well be dampened under humid conditions because OMSs could be easily poisoned in the presence of water vapor. C2H6-selective adsorbents with less hydrophilic environments, on the other hand, not only could effectively minimize the impact of humidity on separation capacity but also could directly produce high-purity C2H4 from C2H6/C2H4 mixtures. Here, we report a C2H6-selective MOF (JNU-2) underlying a rare xae topology. Its cage-like cavities are interconnected through apertures with a limiting diameter of ca. 3.7 Å, which is in the domain of kinetic diameters of C2H4 and C2H6 molecules. Molecular modeling studies suggest the four oxygen atoms on aperture are poised to preferentially interact with C2H6 through multiple C–H···O hydrogen bonding, rendering JNU-2 an enhanced C2H6 selectivity. Indeed, experimental results reveal that JNU-2 not only takes up a great amount of C2H6 comparable to other top-performing C2H6-selective MOFs but also displays excellent separation capacity even under humid conditions; moreover, it can be easily regenerated at room temperature owing to its moderate adsorption enthalpy. This work successfully demonstrated a strategy of balancing adsorption capacity and selectivity for C2H6 by designing MOF materials with cavities interconnected through tailored apertures. The apertures function as screening sites for C2H6 selectivity, while the internal cavities provide space for large adsorption.带有开放金属位点（open metal sites, OMSs）的金属有机框架（metal–organic frameworks, MOFs）已被证实可通过π络合作用优先吸附乙烯（C₂H₄）等不饱和烃类。然而，在潮湿环境下其吸附容量与选择性往往会显著降低，这是因为水蒸气极易使开放金属位点失活。相比之下，具有弱亲水环境的乙烷（C₂H₆）选择性吸附剂，不仅可有效削弱湿度对分离性能的负面影响，还能直接从乙烷/乙烯混合体系中制备高纯度乙烯。 本工作报道了一种具有罕见xae拓扑（xae topology）的乙烷选择性MOF（JNU-2）。该材料的笼状空腔通过极限直径约3.7埃的孔窗相互连通，该孔径尺寸处于乙烯与乙烷分子的动力学直径范围之内。分子模拟研究表明，孔窗处的四个氧原子可通过多重C–H···O氢键与乙烷优先相互作用，使得JNU-2具备优异的乙烷选择性。 实验结果证实，JNU-2不仅吸附的乙烷容量可与其他性能顶尖的乙烷选择性MOF相媲美，即便在潮湿环境下仍展现出卓越的分离性能；此外，因其吸附焓适中，该材料可在室温下轻松实现再生。 本工作成功验证了一种设计策略：通过构建孔窗定制化连通的笼状空腔MOF材料，可平衡乙烷吸附的容量与选择性。其中孔窗充当乙烷选择性的筛分位点，而内部空腔则为大规模吸附提供充足空间。