A Joint Experimental/Computational Exploration of the Dynamics of Confined Water/Zr-Based MOFs Systems

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• 作者：Arnaud Planchais ; Sabine Devautour-Vinot ; Fabrice Salles ; Florence Ragon ; Thomas Devic ; Christian Serre ; Guillaume Maurin
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：July 3, 2014
• 年：2014
• 卷：118
• 期：26
• 页码：14441-14448
• 全文大小：346K
• ISSN：1932-7455

文摘

A joint modeling (molecular dynamics simulations)/experimental (broadband dielectric spectroscopy) approach was conducted to investigate the water adsorption in the UiO-66(Zr) MOF, and its functionalized versions bearing acidic polar groups (鈭扖OOH or 2-COOH per linker). It was first pointed out that the proton conduction measured at room temperature increases with (i) the water uptake and (ii) the concentration of the free acidic carboxylic functions. This trend was further analyzed in light of the preferential arrangements of water within the pores of each MOF as elucidated by molecular dynamics simulations. Indeed, it was revealed that the guest molecules preferentially (i) form interconnected clusters within the UiO-66(Zr)s cages and generate a H-bond network responsible for the proton propagation and (ii) strongly interact with the 鈭扖OOH grafted functions, resulting in the creation of additional charge carriers in the case of the hydrated functionalized solids. Broadband dielectric spectroscopy shed light on how these water configurations impact the local dynamics of both the water molecules and the MOF frameworks. The dielectric relaxation investigation evidenced the existence of one or two relaxation processes, depending on the nature of the UiO-66(Zr) framework and its hydration level. Compared to the dielectric behavior of water confined in a large variety of media, it was thus concluded that the fastest process corresponds to the dynamics of the water molecules forming clusters, while the slowest process is due to the concerted local motion of water/ligand entities.