Gu Chenkai, Yu Zhenzi, Liu Jing, Sholl David S
State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States.
ACS Appl Mater Interfaces. 2021 Mar 10;13(9):11039-11049. doi: 10.1021/acsami.1c00152. Epub 2021 Mar 1.
The separation of xenon/krypton (Xe/Kr) mixtures is a challenging process. Many porous materials allow the adsorption of both Xe and Kr but only with low selectivity. Anion-pillared metal-organic frameworks (MOFs), featuring the anion groups as structural pillars, show potential in gas separations, but only a limited number of them have been synthesized. Here, we describe a collection of 936 anion-pillared MOFs based on 22 experimentally available structures. We performed density functional theory (DFT) optimization and then assigned density-derived electrostatic and chemical (DDEC) charges for each MOF to make them well suited to molecular simulations. The structural properties of the MOFs vary more strongly with the choice of the organic ligand than with other aspects like fluorine groups and metal centers. We then screened the entire collection of MOFs in the context of Xe/Kr separation at room temperature. Compared with previously reported MOFs, the interpenetrated MOF SIFSIX-6-Cd-i is predicted to perform better for Xe/Kr separations, with a good balance between working capacity (1.62 mmol/g) and separation selectivity (16.4) at 298 K and 100 kPa. We also found that the heterogeneity of fluorine groups within a MOF can help to enhance Xe working capacity without reducing the Xe/Kr selectivity, suggesting that synthesis of anion-pillared MOFs with mixed fluorine groups may lead to improved Xe/Kr separation performance.
氙/氪（Xe/Kr）混合物的分离是一个具有挑战性的过程。许多多孔材料能够吸附Xe和Kr，但选择性很低。以阴离子基团作为结构支柱的阴离子柱撑金属有机框架（MOF）在气体分离方面显示出潜力，但目前仅合成了有限数量的此类材料。在此，我们基于22种实验可得的结构描述了936种阴离子柱撑MOF的集合。我们进行了密度泛函理论（DFT）优化，然后为每个MOF分配了密度衍生的静电和化学（DDEC）电荷，使其非常适合分子模拟。MOF的结构性质随有机配体的选择变化比随氟基团和金属中心等其他方面的变化更为强烈。然后，我们在室温下Xe/Kr分离的背景下对整个MOF集合进行了筛选。与先前报道的MOF相比，互穿MOF SIFSIX - 6 - Cd - i预计在Xe/Kr分离方面表现更好，在298 K和100 kPa下工作容量（1.62 mmol/g）和分离选择性（16.4）之间具有良好的平衡。我们还发现，MOF内氟基团的不均匀性有助于提高Xe的工作容量而不降低Xe/Kr选择性，并表明合成具有混合氟基团的阴离子柱撑MOF可能会导致Xe/Kr分离性能的改善。
