Conformation-Controlled Sorption Properties and Breathing of the Aliphatic Al-MOF [Al(OH)(CDC)]
Conformation-Controlled Sorption Properties and Breathing of the Aliphatic Al-MOF [Al(OH)(CDC)]
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DOI：
10.1021/ic500288w
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发表时间：
2014-05-05
影响因子：
4.6
通讯作者：
Stock, Norbert
中科院分区：
文献类型：
--
作者：
Niekiel, Felicitas;Lannoeye, Jeroen;Stock, Norbert
Al-MOF CAU-13（[Al(OH)(trans-CDC)]；trans-H2CDC = trans-1,4-环己烷二甲酸）在结构上与 MIL-53 化合物相关，MIL-53 化合物以其“呼吸”行为而闻名，即在外部刺激（例如吸附物分子的存在）下的框架灵活性。对CAU-13的吸附性能进行了详细研究。记录 N-2、H-2、CH4、CO、CO2 和水的吸附等温线，并通过微量热法测定气体的吸附焓。通过原位同步加速器粉末 X 射线衍射 (PXRD) 跟踪 CO2 吸附后的结构变化。通过参数晶胞细化对模式进行分析，并通过密度泛函理论计算对 CO2 分子的优先排列进行建模。从均三甲苯中吸附和分离邻、间和对二甲苯混合物显示出邻二甲苯的优先吸附。由 PXRD 数据确定了负载邻/间/对二甲苯的 CAU-13 的结构。二甲苯异构体的吸附导致比 CAU-13 热活化更大的孔开口。在活化样品CAU-13（空孔）的晶体结构中，一半的连接体采用a,a构象，另一半采用e,e构象，并且a,a-CDC2-离子的存在阻碍了CAU-13的结构灵活性。然而，吸附二甲苯后，所有连接体均以 e,e 构象存在，从而通过这种新型“呼吸”打开更宽的孔。
The Al-MOF CAU-13 ([Al(OH)(trans-CDC)]; trans-H2CDC = trans-1,4-cyclohexanedicarboxylic acid) is structurally related to the MIL-53 compounds that are well-known for their "breathing" behavior, i.e., the framework flexibility upon external stimuli such as the presence of adsorbate molecules. The adsorption properties of CAU-13 were investigated in detail. The sorption isotherms of N-2, H-2, CH4, CO, CO2, and water were recorded, and the adsorption enthalpies for the gases were determined by microcalorimetry. The structural changes upon adsorption of CO2 were followed with in situ synchrotron powder X-ray diffraction (PXRD). The patterns were analyzed by parametric unit cell refinement, and the preferential arrangement of the CO2 molecules was modeled by density functional theory calculations. The adsorption and separation of mixtures of o-, m-, and p-xylene from mesitylene showed a preferred adsorption of o-xylene. The structures of o/m/p-xylene-loaded CAU-13 were determined from PXRD data. The adsorption of xylene isomers induces a larger pore opening than that in the thermal activation of CAU-13. In the crystal structure of the activated sample CAU-13(empty pore), half of the linkers adopt the a,a confirmation and the other half the e,e conformation, and the presence of a,a-CDC2- ions hampers the structural flexibility of CAU-13. However, after the adsorption of xylene, all linkers are present in the e,e conformation, allowing for a wider pore opening by this new type of "breathing".