†Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.
∥ Wolfson Northern Carbon Research Laboratories, School of Chemical Engineering and Advanced Materials, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom.
J Am Chem Soc. 2015 May 6;137(17):5706-19. doi: 10.1021/ja511878b. Epub 2015 Apr 22.
Metal-organic frameworks (MOFs) are known to facilitate energy-efficient separations of important industrial chemical feedstocks. Here, we report how a class of green MOFs-namely CD-MOFs-exhibits high shape selectivity toward aromatic hydrocarbons. CD-MOFs, which consist of an extended porous network of γ-cyclodextrins (γ-CDs) and alkali metal cations, can separate a wide range of benzenoid compounds as a result of their relative orientation and packing within the transverse channels formed from linking (γ-CD)6 body-centered cuboids in three dimensions. Adsorption isotherms and liquid-phase chromatographic measurements indicate a retention order of ortho- > meta- > para-xylene. The persistence of this regioselectivity is also observed during the liquid-phase chromatography of the ethyltoluene and cymene regioisomers. In addition, molecular shape-sorting within CD-MOFs facilitates the separation of the industrially relevant BTEX (benzene, toluene, ethylbenzene, and xylene isomers) mixture. The high resolution and large separation factors exhibited by CD-MOFs for benzene and these alkylaromatics provide an efficient, reliable, and green alternative to current isolation protocols. Furthermore, the isolation of the regioisomers of (i) ethyltoluene and (ii) cymene, together with the purification of (iii) cumene from its major impurities (benzene, n-propylbenzene, and diisopropylbenzene) highlight the specificity of the shape selectivity exhibited by CD-MOFs. Grand canonical Monte Carlo simulations and single component static vapor adsorption isotherms and kinetics reveal the origin of the shape selectivity and provide insight into the capability of CD-MOFs to serve as versatile separation platforms derived from renewable sources.
金属有机骨架（MOFs）被广泛应用于促进重要工业化学原料的节能分离。在此，我们报告了一类绿色 MOFs——即 CD-MOFs，它对芳烃表现出高的形状选择性。CD-MOFs 由 γ-环糊精（γ-CDs）和碱金属阳离子组成的扩展多孔网络构成，由于其在横向通道中的相对取向和堆积，能够分离广泛的苯系化合物，这些通道是由连接（γ-CD）6 体心立方的三维结构形成的。吸附等温线和液相色谱测量表明，邻二甲苯>间二甲苯>对二甲苯的保留顺序。这种区域选择性在乙基甲苯和对异丙基甲苯的液相色谱中也得到了保留。此外，CD-MOF 内的分子形状分选有利于分离工业相关的 BTEX（苯、甲苯、乙苯和二甲苯异构体）混合物。CD-MOF 对苯和这些烷基芳烃表现出的高分辨率和大分离因子，为当前的分离方案提供了一种高效、可靠和绿色的替代方案。此外，（i）乙基甲苯和（ii）对异丙基甲苯的区域异构体的分离，以及（iii）异丙苯从其主要杂质（苯、正丙苯和二异丙苯）的纯化，突出了 CD-MOFs 所表现出的形状选择性的特异性。巨正则蒙特卡罗模拟和单组分静态蒸汽吸附等温线和动力学揭示了形状选择性的起源，并深入了解了 CD-MOF 作为可再生资源衍生的多功能分离平台的能力。
