CNRS-ENS-UPMC, Département de Chimie, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France.
Phys Chem Chem Phys. 2013 Nov 21;15(43):19049-56. doi: 10.1039/c3cp53126k.
The hydration behavior of metal-organic frameworks (MOFs) is of interest both from a practical and from a fundamental point of view: it is linked, on the one hand, to the hydrothermal stability (or instability) of the nanoporous material, which might limit its use in technological applications. On the other hand, it sheds light on the behavior of water in a strongly confined environment. Here, we use first-principles molecular dynamics (MD) to investigate two hydrated phases of the flexible MOF MIL-53(Cr), which adopts a narrow- or a large-pore form, depending on the water loading. Structure and dynamics of the two phases are thoroughly analyzed and compared, with a focus on the hydroxyl group of MIL-53(Cr) and the water molecules in the nanopores. Furthermore, the behavior of the confined water is compared to that of bulk water. Whereas in the narrow-pore form, water is adsorbed at specific crystalline sites, it shows a more disordered, bulk-like structure in the large-pore form. However, reorientation dynamics of water molecules in the latter is considerably slowed down with respect to bulk water, which highlights the confinement effect of the nanoporous framework.
金属-有机骨架（MOFs）的水合行为无论从实际应用还是从基础理论角度来看都很有意义：一方面，它与纳米多孔材料的水热稳定性（或不稳定性）有关，这可能限制了其在技术应用中的使用。另一方面，它揭示了在强烈受限环境中水分子的行为。在这里，我们使用第一性原理分子动力学（MD）来研究柔性 MOF MIL-53(Cr)的两种水合相，这取决于水的负载量，MIL-53(Cr) 可以采用窄孔或大孔形式。我们彻底分析和比较了这两种相的结构和动力学，重点关注 MIL-53(Cr) 的羟基和纳米孔中的水分子。此外，还比较了受限水和体相水的行为。在窄孔形式中，水被吸附在特定的晶格格点上，而在大孔形式中，水呈现出更无序、类似体相的结构。然而，与体相水相比，后者中水分子的重取向动力学大大减慢，这突出了纳米多孔骨架的受限效应。
