Krause Simon, Bon Volodymyr, Du Hongchu, Dunin-Borkowski Rafal E, Stoeck Ulrich, Senkovska Irena, Kaskel Stefan
Chair of Inorganic Chemistry, Technische Universität Dresden, Bergstrasse 66, 01062 Dresden, Germany.
Centre for Systems Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Beilstein J Nanotechnol. 2019 Aug 20;10:1737-1744. doi: 10.3762/bjnano.10.169. eCollection 2019.
In this contribution we analyze the influence of adsorption cycling, crystal size, and temperature on the switching behavior of the flexible Zr-based metal-organic framework DUT-98. We observe a shift in the gate-opening pressure upon cycling of adsorption experiments for micrometer-sized crystals and assign this to a fragmentation of the crystals. In a series of samples, the average crystal size of DUT-98 crystals was varied from 120 µm to 50 nm and the obtained solids were characterized by X-ray diffraction, infrared spectroscopy, as well as scanning and transmission electron microscopy. We analyzed the adsorption behavior by nitrogen and water adsorption at 77 K and 298 K, respectively, and show that adsorption-induced flexibility is only observed for micrometer-sized crystals. Nanometer-sized crystals were found to exhibit reversible type I adsorption behavior upon adsorption of nitrogen and exhibit a crystal-size-dependent steep water uptake of up to 20 mmol g at 0.5 / with potential for water harvesting and heat pump applications. We furthermore investigate the temperature-induced structural transition by in situ powder X-ray diffraction. At temperatures beyond 110 °C, the open-pore state of the nanometer-sized DUT-98 crystals is found to irreversibly transform to a closed-pore state. The connection of crystal fragmentation upon adsorption cycling and the crystal size dependence of the adsorption-induced flexibility is an important finding for evaluation of these materials in future adsorption-based applications. This work thus extends the limited amount of studies on crystal size effects in flexible MOFs and hopefully motivates further investigations in this field.
在本论文中，我们分析了吸附循环、晶体尺寸和温度对柔性锆基金属有机框架材料DUT-98开关行为的影响。我们观察到，对于微米级晶体，吸附实验循环时的开闸压力发生了偏移，并将此归因于晶体的破碎。在一系列样品中，DUT-98晶体的平均晶体尺寸从120 µm变化到50 nm，通过X射线衍射、红外光谱以及扫描和透射电子显微镜对所得固体进行了表征。我们分别在77 K和298 K下通过氮气和水吸附分析了吸附行为，结果表明仅在微米级晶体中观察到吸附诱导的柔性。发现纳米级晶体在吸附氮气时表现出可逆的I型吸附行为，并且在0.5 / 时表现出与晶体尺寸相关的高达20 mmol g的陡峭水吸收，具有用于水收集和热泵应用的潜力。我们还通过原位粉末X射线衍射研究了温度诱导的结构转变。在超过110 °C的温度下，发现纳米级DUT-98晶体的开孔状态不可逆地转变为闭孔状态。吸附循环时晶体破碎与吸附诱导柔性的晶体尺寸依赖性之间的联系，是评估这些材料在未来基于吸附的应用中的一个重要发现。因此，这项工作扩展了对柔性金属有机框架中晶体尺寸效应的有限研究，并有望激发该领域的进一步研究。
