Abstract
We present a dielectric spectroscopy study of dipolar dynamics in the hydrated UiO-66(Zr) type metal-organic frameworks (MOFs) functionalized with −NH2 and −F groups. Experiments are performed in a broad temperature and frequency ranges allowing us to probe several dipolar relaxations. For both samples at temperature below 220 K, we observe confined supercooled water dynamics, which can be described by the Arrhenius law. At slightly higher temperature, a second less pronounced dipolar relaxation is identified, and its origin is discussed. At even higher temperature, the dielectric permittivity exhibits anomalous increase with increasing temperature due to the proton conductivity. Upon further heating, the permittivity shows a sudden decrease indicating a reversible removal of water molecules. Measurements of the dehydrated samples reveal absence of all three dipolar processes.
Highlights
Metal-organic frameworks (MOFs) are crystalline compounds consisting of metal centers joined together by organic linkers into highly porous structures [1]
One of the most popular members of these compounds is UiO-66(Zr) metal-organic frameworks (MOFs) consisting of Zr6 O4 (OH)4 secondary building units (SBUs), which are connected by 1,4-benzene-dicarboxylate (BDC) linkers into porous structures with Fm3̄m face-centered cubic structure [11]
First we performed temperature dependent dielectric spectroscopy experiments of UiO-66-NH2 and UiO-66-F4 powder samples starting from the hydrated forms
Summary
Metal-organic frameworks (MOFs) are crystalline compounds consisting of metal centers joined together by organic linkers into highly porous structures [1]. The high porosity and tunability of these compounds is expected to be utilized for selective gas adsorption [3,4], separation [5], and storage [6,7] as well as chemical catalysis [8], drug delivery [9]. Oslo), which exhibit superior thermal and chemical stability as well as high porosity [11]. One of the most popular members of these compounds is UiO-66(Zr) MOF consisting of Zr6 O4 (OH) secondary building units (SBUs), which are connected by 1,4-benzene-dicarboxylate (BDC) linkers into porous structures with Fm3̄m face-centered cubic structure (see Figure 1) [11]. The framework has octahedral pores connected to smaller tetrahedral cavities via relatively narrow windows of about 5 Å diameter
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