在金属有机框架中对超冷水的动态进行2H NMR研究
Verena Schiller1, Katharina Knippen2, Alois Loidl3
1Institute for Condensed Matter Physics, Technische Universität Darmstadt, Hochschulstraße 6, 64289 Darmstadt, Germany.
我们使用2H核磁共振 (NMR) 来研究MFU-4l中的水动力学. 在冷却时,水的重定向从散装式行为过渡到非ergodic动态,受孔径大小和连接性的影响.
科学领域:
- 材料科学 材料科学 材料科学
- 物理化学 物理化学
- 化学物理 化学物理
背景情况:
- 封闭在多孔材料中的水表现出独特的动态特性,与散装水不同.
- 金属有机框架 (MOF) 提供可调节的孔隙环境,用于研究封闭效应.
- MFU-4l是一种MOF,具有球形毛孔 (1.2和1.9纳米) 的正规3D网络.
研究的目的:
- 为了研究重水 (D2O) 限制在MFU-4l金属有机框架内的重水 (D2O) 的重定向和扩散动态.
- 为了阐明受限下水动态的温度依赖性行为.
- 将发现与类似系统中水 (H2O) 的现有数据进行比较.
主要方法:
- 2H核磁共振 (NMR) 光谱被用来探测D2O的动态.
- 分析了旋转相关时间和旋转格子放松.
- 数据与宽带介电谱学 (BDS) 结果进行了比较.
主要成果:
- 旋转相关时间遵循Vogel-Fulcher-Tammann在~225 K以上和Arrhenius在~170 K以下的行为,其中有一个交叉.
- 核磁共振结果与类似框架中的H2O之前的BDS数据保持一致.
- 在低温下观察到大量结构 (α) 放松和非指数自旋格子放松的证据,表明异质动态.
结论:
- 在MFU-4l中,水的动态在冷却后从散装型转变为非ergodic行为.
- 限制对水的重定向的影响主要取决于孔径 (~2 nm),而扩散则对孔径连接和拓敏感.
- 观察到的异质性可能来自散装或受限诱导的属性.
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