Zhang Li, Wang Qi, Wu Tao, Liu Ying-Chun
Department of Chemistry, Zhejiang University, Hangzhou 310027, P.R. China.
Chemistry. 2007;13(22):6387-96. doi: 10.1002/chem.200700205.
Novel metal-organic frameworks (MOFs) may lead to advances in adsorption and catalysis owing to their superior properties compared to traditional nanoporous materials. A combination of the grand canonical Monte Carlo method and configurational-bias Monte Carlo simulation was used to evaluate the adsorption isotherms of C4-C6 alkane isomer mixtures in IRMOF-1 and IRMOF-6. The amounts of adsorbed linear and branched alkanes increase with increasing pressure, and the amount of branched alkanes is larger than that of the linear ones. The locations of the alkane isomer reveal that the Zn4O clusters of the IRMOFs are the preferential adsorption sites for the adsorbate molecules. The interaction energy between the Zn4O cluster and the adsorbate is larger than that between the organic linker and the adsorbate. It was further confirmed that the Zn4O cluster plays a much more important role in adsorption by pushing a probe molecule into the pore at positions closer to the Zn4O cluster. It is difficult for branched alkane molecules to approach the Zn4O cluster of IRMOF-6 closely owing to strong spatial hindrance. In addition, the adsorption selectivity is discussed from the viewpoints of thermodynamics and kinetics, and the diffusion behavior of n-butane and 2-methylpropane were investigated to illustrate the relationship between diffusion and adsorption.
新型金属有机框架材料（MOFs）由于其相较于传统纳米多孔材料的优越性能，可能会在吸附和催化领域取得进展。采用巨正则蒙特卡罗方法和构型偏倚蒙特卡罗模拟相结合的方式，来评估C4 - C6烷烃异构体混合物在IRMOF - 1和IRMOF - 6中的吸附等温线。随着压力升高，直链和支链烷烃的吸附量均增加，且支链烷烃的吸附量大于直链烷烃。烷烃异构体的吸附位置表明，IRMOFs的Zn4O簇是被吸附分子的优先吸附位点。Zn4O簇与被吸附物之间的相互作用能大于有机连接体与被吸附物之间的相互作用能。通过将探针分子推至更靠近Zn4O簇的孔位置，进一步证实了Zn4O簇在吸附过程中发挥着更为重要的作用。由于强大的空间位阻，支链烷烃分子难以靠近IRMOF - 6的Zn4O簇。此外，从热力学和动力学角度讨论了吸附选择性，并研究了正丁烷和2 - 甲基丙烷的扩散行为，以阐明扩散与吸附之间的关系。
