Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, Illinois 61801, USA.
Langmuir. 2010 Jul 6;26(13):11319-29. doi: 10.1021/la100635r.
Metal-organic frameworks have been proposed as useful sorbents for the capture of a variety of compounds. In this work, inverse gas chromatography (IGC) utilizing micropacked capillary columns was used to probe the adsorption of more than 30 volatile organic compounds (VOCs) on IRMOF-1. In an attempt to study the effect of structural degradation upon VOC adsorption, multiple samples of IRMOF-1 with widely ranging properties were investigated. Trends in the differential enthalpies and equilibrium constants for the adsorption of VOCs were determined on the basis of the molecular properties of the adsorbate and the structural properties of the MOF sample. The results indicate that samples of IRMOF-1 that are affected by a moderate amount of structural degradation interact with adsorbed species more strongly than does a sample with fewer defects, resulting in higher heats of adsorption. Samples of IRMOF-1 with specific surface areas of around 1000 m(2)/g show heats of adsorption for alkanes that are higher than those estimated previously via Monte Carlo calculations. Although the data for nonpolar (and weakly polar) species showed many of the anticipated trends for the interactions with IRMOF-1, the equilibrium behavior of polar VOCs did not correlate well with the molecular properties of the adsorbate (i.e., vapor pressure and deformation polarizability), leaving some uncertainty about the nature of the interaction mechanism. The equilibrium data and the heats of adsorption were found to fit well to a small group of molecular descriptors through the application of the Abraham linear free-energy relationship, thus providing insight into the complex interactions between the MOF structure and the VOC compounds. Hydrogen bonding interactions were determined to be the primary contributors to specific interactions between adsorbates and the MOF surface. Size exclusion also seems to play a role in the adsorption of larger species. These results show that the interaction of VOCs with MOFs is more complex than previously assumed and that more work is needed to probe the mechanisms of these processes.
金属有机骨架已被提议作为各种化合物捕获的有用吸附剂。在这项工作中，利用微填充毛细管柱的反气相色谱（IGC）用于探测超过 30 种挥发性有机化合物（VOCs）在 IRMOF-1 上的吸附。为了研究结构降解对 VOC 吸附的影响，研究了具有广泛性质的多个 IRMOF-1 样品。根据吸附质的分子性质和 MOF 样品的结构性质，确定了 VOC 吸附的差分焓和平衡常数的趋势。结果表明，受中度结构降解影响的 IRMOF-1 样品与吸附物种相互作用比缺陷较少的样品更强，导致吸附热更高。比表面积约为 1000 m(2)/g 的 IRMOF-1 样品对烷烃的吸附热高于通过蒙特卡罗计算先前估计的值。尽管非极性（和弱极性）物质的数据显示了与 IRMOF-1 相互作用的许多预期趋势，但极性 VOC 的平衡行为与吸附质的分子性质（即蒸气压和变形极化率）相关性不佳，这使得相互作用机制的性质存在一些不确定性。通过应用 Abraham 线性自由能关系，发现平衡数据和吸附热非常适合一小组分子描述符，从而深入了解 MOF 结构与 VOC 化合物之间的复杂相互作用。氢键相互作用被确定为吸附质与 MOF 表面之间特定相互作用的主要贡献者。尺寸排阻似乎也在较大物种的吸附中起作用。这些结果表明，VOC 与 MOF 的相互作用比以前假设的更为复杂，需要进一步研究这些过程的机制。
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