Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
Phys Chem Chem Phys. 2010 Oct 21;12(39):12621-9. doi: 10.1039/c0cp00092b. Epub 2010 Aug 23.
Grand canonical Monte Carlo simulations were performed to identify trends in low-pressure adsorption of a broad range of organic molecules by a set of metal-organic frameworks (MOFs). While previous simulation studies focused on the adsorption of small molecules such as carbon dioxide and methane, we consider more complicated organic molecules relevant to chemical sensing and detection: small aromatics (o-, m-, and p-xylene), polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene), explosives (TNT and RDX), and chemical warfare agents (GA and VM). The framework materials include several Zn-IRMOFs (IRMOFs 1-3, 7, 8), a Cr-MOF (CrMIL-53lp), and a Cu-MOF (HKUST-1). A wide range of loading pressures is examined, extending from 100 ppm to 10 ppb in air, thus spanning the entire range of conditions relevant to chemical sensing for security, environmental, and industrial process monitoring. Our results are validated by comparing calculated adsorption energies with experimental values, where available. Many of the larger organics are significantly adsorbed by the target MOFs at low pressure, which is consistent with the high isosteric heats of adsorption (12 kcal mol(-1)-49 kcal mol(-1)) computed for these analytes. These adsorption energies are significantly large that interference from atmospheric components should not interfere with chemical detection at low pressures. We show that pi-pi stacking interactions are an important contributor to these high heats of adsorption. CrMIL-53lp shows the highest adsorption energy for all analytes, suggesting that this material may be suitable for detection of low-level organics. At higher loading pressures, the Zn-MOFs show a much higher volumetric uptake than either CrMIL-53lp or HKUST-1 for all types of analyte considered here. Within the Zn-IRMOF series, analyte loading is proportional to accessible free volume, and loading decreases with increasing analyte size due to molecular packing effects. Overall, the results demonstrate that atomistic simulation can be used as an efficient first step in the screening of MOFs for detection of large molecules. For example, at the 10 ppb level, all of the Zn-IRMOFs are able to distinguish between TNT and the structurally similar xylenes.
采用巨正则蒙特卡罗模拟方法研究了一系列金属有机骨架（MOF）对多种有机分子在低压下的吸附趋势。虽然之前的模拟研究主要集中在二氧化碳和甲烷等小分子的吸附上，但我们考虑了与化学传感和检测更相关的更复杂的有机分子：小芳烃（邻、间、对二甲苯）、多环芳烃（萘、蒽、菲）、爆炸物（TNT 和 RDX）和化学战剂（GA 和 VM）。所研究的骨架材料包括几种 Zn-IRMOFs（IRMOFs 1-3、7、8）、一种 Cr-MOF（CrMIL-53lp）和一种 Cu-MOF（HKUST-1）。研究了很宽的负载压力范围，从空气中的 100ppm 到 10ppb，因此涵盖了与安全、环境和工业过程监测相关的整个化学传感条件范围。我们通过将计算出的吸附能与实验值进行比较来验证我们的结果，在可用的情况下。许多较大的有机分子在低压下被目标 MOF 显著吸附，这与为这些分析物计算的高等吸附热（12kcal/mol-49kcal/mol）一致。这些吸附能非常大，以至于大气成分的干扰不应在低压下干扰化学检测。我们表明，pi-pi 堆积相互作用是这些高吸附热的重要贡献者。CrMIL-53lp 对所有分析物都表现出最高的吸附能，这表明该材料可能适用于低水平有机化合物的检测。在更高的负载压力下，与 CrMIL-53lp 或 HKUST-1 相比，Zn-MOF 对所有考虑的分析物类型都表现出更高的体积吸收率。在 Zn-IRMOF 系列中，分析物的负载与可及的自由体积成正比，并且由于分子堆积效应，随着分析物尺寸的增加，负载减小。总的来说，结果表明，原子模拟可以作为筛选用于检测大分子的 MOF 的有效第一步。例如，在 10ppb 水平下，所有 Zn-IRMOF 都能够区分 TNT 和结构相似的二甲苯。
