Engineering New Defective Phases of UiO Family Metal-Organic Frameworks with Water

Abstract

As defects significantly affect the properties of metal-organic frameworks (MOFs)–from changing their mechanical properties to enhancing their catalytic ability–obtaining synthetic control over defects is essential to tuning the effects on the properties of the MOF. Previous work has shown that synthesis temperature and the identity and concentration of modulating acid are critical factors in determining the nature and distribution of defects in the UiO family of MOFs. In this paper we demonstrate that the amount of water in the reaction mixture in the synthesis of UiO family MOFs is an equally important factor, as it controls the phase which forms for both UiO-67(Hf)<br>and UiO-66(Hf) (F4BDC). We use this new understanding of the importance of water to develop a new route to the stable defect-ordered <b>hcp</b> UiO-66(Hf) phase, demonstrating the effectiveness of this method of defect-engineering in the rational design of MOFs. The insights provided by this<br>investigation open up the possibility of harnessing defects to produce new phases and dimensionalities of other MOFs, including nanosheets, for a variety of applications such as MOF-based membranes.

Controlling the Synthesis of Metal–Organic Framework UiO-67 by Tuning Its Kinetic Driving Force

“…90,136 Figure 36a presents the PXRD pattern of the samples synthesized with ZrCl4 and shows that the results are in agreement with the reported work. 121 The diffraction pattern for hexagonal nanosheets phase is identical with that of the reported diffraction pattern for hexagonal nanosheets phase. However, the obtained diffraction pattern of hcp phase has few forbidden peaks (Figure 36b).…”

“…Further, the PXRD for the samples at 24 h shows that there is a presence of forbidden peaks in the diffraction pattern suggesting the formation of other type of phases(Figure 31). This behavior can be attributed to a small amount of loss of water during the extraction of samples during the course of the experiment, knowing the literature report where water plays an important role in determining phase of MOF material 77,121. In combination, these results led to a systematic screening of amount of water for the synthesis of UiO-67 under concentrated synthesis conditions.…”

“…135 Grey and coworkers have reported a study showing the formation of new defective phases of Zr and H2bpdc linker with varying amounts of water. 121 This study was performed on the Hafnium (Hf) analogues of UiO-66 and UiO-67 where the different phases of the material are observed depending on the amount of water in the synthesis.…”

Direct Imaging of Correlated Defect Nanodomains in a Metal-Organic Framework

“…Previous work has demonstrated that the concentration of modulating ligands, such as formate or water, in the reaction mixture dictates the competitive formation of reo and fcu. [4][5][6] Our observations are consistent with local fluctuations in concentration during crystal growth controling the local phase competition. While formate is in substantial excess, terephthalate binds more strongly.…”

“…The {211} type planes pass through metal clusters and the cluster-ligand attachment sites, which may be linked to the mechanism by which formate modulators compete with terephthalate linkers. [4][5][6] Our multiscale structural analysis shows that defect nanodomains in defect-engineered UiO-66(Hf) exhibit a block-like lamellar morphology and occur in a preferred orientation, extending perpendicular to {111} planes and sometimes perpendicular to other low index facets, with interfaces between reo and fcu domains on {211} planes. These characteristics remain similar across systematically varied defect densities but become more evident at high defect density.…”