金属有机骨架中的额外吸附和吸附超晶格形成,Nature

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金属有机骨架中的额外吸附和吸附超晶格形成
Nature ( IF 50.5 ) Pub Date : 2015-11-01 , DOI: 10.1038/nature15734
Hae Sung Cho , Hexiang Deng , Keiichi Miyasaka , Zhiyue Dong , Minhyung Cho , Alexander V. Neimark , Jeung Ku Kang , Omar M. Yaghi , Osamu Terasaki

金属有机骨架 (MOF) 具有高内表面积和广泛可调的成分，这使其可用于涉及吸附的应用，例如氢气、甲烷或二氧化碳存储。吸附过程的选择性和吸收能力由涉及被吸附物及其多孔主体材料的相互作用决定。但是，尽管吸附质分子与内部 MOF 表面以及它们之间在单个孔内的相互作用已被广泛研究，但尚未探索跨孔壁的吸附质 - 吸附质相互作用。在这里，我们表明由孔隙填充引起的 MOF 中的局部应变可以引起集体和远程吸附质 - 吸附质相互作用以及超出原始 MOF 晶胞的吸附质超晶格的形成。具体来说，我们使用原位小角度 X 射线散射来跟踪和映射介孔 MOF-74 系列的五个成员中吸附分子的分布和顺序，沿着整个吸附 - 解吸等温线。我们发现在所有情况下，填充孔隙的毛细管凝结会导致形成“额外吸附域”——即跨越几个相邻孔隙的域，其吸附物密度高于非域孔隙。在一个 MOF 的情况下，IRMOF-74-V-hex，这些域形成了一种超晶格结构，很难与普遍认为的孔隙填充是一种随机过程的观点相协调。我们的数据提供的吸附过程的可视化，有明确的证据表明初始吸附物聚集在不同的域中，并在最终达到均匀分布之前排序，

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Extra adsorption and adsorbate superlattice formation in metal-organic frameworks

Metal-organic frameworks (MOFs) have a high internal surface area and widely tunable composition, which make them useful for applications involving adsorption, such as hydrogen, methane or carbon dioxide storage. The selectivity and uptake capacity of the adsorption process are determined by interactions involving the adsorbates and their porous host materials. But, although the interactions of adsorbate molecules with the internal MOF surface and also amongst themselves within individual pores have been extensively studied, adsorbate–adsorbate interactions across pore walls have not been explored. Here we show that local strain in the MOF, induced by pore filling, can give rise to collective and long-range adsorbate–adsorbate interactions and the formation of adsorbate superlattices that extend beyond an original MOF unit cell. Specifically, we use in situ small-angle X-ray scattering to track and map the distribution and ordering of adsorbate molecules in five members of the mesoporous MOF-74 series along entire adsorption–desorption isotherms. We find in all cases that the capillary condensation that fills the pores gives rise to the formation of ‘extra adsorption domains’—that is, domains spanning several neighbouring pores, which have a higher adsorbate density than non-domain pores. In the case of one MOF, IRMOF-74-V-hex, these domains form a superlattice structure that is difficult to reconcile with the prevailing view of pore-filling as a stochastic process. The visualization of the adsorption process provided by our data, with clear evidence for initial adsorbate aggregation in distinct domains and ordering before an even distribution is finally reached, should help to improve our understanding of this process and may thereby improve our ability to exploit it practically.

更新日期：2015-11-01

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