Valadez Sánchez Elvia P, Knebel Alexander, Izquierdo Sánchez Luis, Klumpp Michael, Wöll Christof, Dittmeyer Roland
Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Institute for Micro Process Engineering (IMVT), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Langmuir. 2020 Jul 28;36(29):8444-8450. doi: 10.1021/acs.langmuir.0c00875. Epub 2020 Jul 13.
Characterizing the adsorption behavior of thin films at technical operation ranges is highly relevant in order to obtain appropriate experimental parameters, as well as to evaluate their possible integration in multiple applications. Nonetheless, gathering such experimental data is not a trivial task. In the case of metal-organic framework thin films, a particular interesting class of highly porous coatings, determination of adsorption isotherms at elevated temperatures and pressures is not commonly reported. Using a custom-designed langatate crystal microbalance following the principle for piezoelectric microbalances, but under harsher conditions, allowed us to present adsorption equilibrium measurements on a zeolitic imidazolate framework-8 (ZIF-8) surface-mounted metal-organic framework (SURMOF) thin film at temperatures between 35 and 100 °C and at a pressure range up to 10 bars. The layer-by-layer liquid-phase epitaxy approach was used to deposit ZIF-8 SURMOF thin films on langatate crystals. X-ray diffraction, infrared reflection absorption spectroscopy, and scanning electron microscopy combined with energy dispersive X-ray mapping were used to gather deeper information on the ZIF-8 thin film growth. Single-component isotherms were collected for different gases of practical interest, that is, CO, CH, CH, CH, and CH. The measurements were obtained at 35, 50, 75, and 100 °C at a gauge pressure range up to 10 bars. The collected data showed a clear preferential adsorption of ethane over ethylene, whereas only a slight difference was found between propane and propylene. Additionally, the experimental data allowed for the determination of adsorption equilibrium constants and saturation loadings of the ZIF-8 material as a thin SURMOF film, which is of great importance for its integration in multiple applications, such as sensor devices or in membrane-based separation.
在技术操作范围内表征薄膜的吸附行为对于获得合适的实验参数以及评估它们在多种应用中的可能集成至关重要。尽管如此，收集此类实验数据并非易事。对于金属有机框架薄膜这一特别有趣的高孔隙率涂层类别，在高温高压下测定吸附等温线的情况并不常见。使用遵循压电微天平原理但在更严苛条件下的定制兰加他敏晶体微天平，使我们能够在35至100°C的温度和高达10巴的压力范围内，对负载在兰加他敏晶体上的沸石咪唑酯骨架-8（ZIF-8）表面安装金属有机框架（SURMOF）薄膜进行吸附平衡测量。采用逐层液相外延法在兰加他敏晶体上沉积ZIF-8 SURMOF薄膜。利用X射线衍射、红外反射吸收光谱以及结合能量色散X射线映射的扫描电子显微镜来深入了解ZIF-8薄膜的生长情况。针对实际感兴趣的不同气体，即一氧化碳、甲烷、乙烷、丙烷和丁烷，收集了单组分等温线。测量是在35、50、75和100°C下，在高达10巴的表压范围内进行的。收集到的数据表明乙烷对乙烯有明显的优先吸附，而丙烷和丙烯之间仅发现细微差异。此外，实验数据有助于确定作为SURMOF薄膜的ZIF-8材料的吸附平衡常数和饱和负载量，这对于其在多种应用中的集成非常重要，例如传感器设备或基于膜的分离应用。
