Felix Bloch Institute for Solid State Physics, Leipzig University, Linnéstr. 5, 04103 Leipzig, Germany.
BASF SE, Carl-Bosch-Str. 38, 67056 Ludwigshafen am Rhein, Germany.
J Phys Chem Lett. 2023 Apr 13;14(14):3391-3396. doi: 10.1021/acs.jpclett.3c00155. Epub 2023 Mar 30.
A nuclear magnetic resonance (NMR) study of a pore opening in amino-functionalized metal-organic framework (MOF) MIL-53(Al) in response to methane pressure variation is presented. Variations of both NMR signal intensities and transversal relaxation rates for methane are found to reveal hysteretic structural transitions in the MOF material, which are smeared out over broad pressure ranges. Experiments with pressure reversals upon an incomplete adsorption/desorption gave deeper insight into the microscopic transition mechanisms. These experiments have unequivocally proven that the non-stepwise pore opening/closing transitions observed in the experiments are governed by a distribution of the opening/closing pressures over different MOF crystallites, for example, due to a distribution of the crystal sizes or shapes. The slow kinetics of the structural transitions measured in the hysteresis regime revealed a complex free energy landscape for the phase transition process.
本文报道了一种通过对氨基功能化金属有机骨架（MOF） MIL-53(Al) 中孔开口在甲烷压力变化下的核磁共振（NMR）研究。发现甲烷的 NMR 信号强度和横向弛豫率的变化均能揭示 MOF 材料中的滞后结构转变，这些转变在较宽的压力范围内被平滑化。在不完全吸附/解吸过程中进行的压力反转实验使我们对微观转变机制有了更深入的了解。这些实验明确证明，在实验中观察到的非逐步孔开口/关闭转变是由不同 MOF 晶体内的开口/关闭压力分布控制的，例如，由于晶体尺寸或形状的分布。在滞后区测量的结构转变的缓慢动力学揭示了相变过程的复杂自由能景观。
