As for other families of microporous materials, the presence of defect sites in metal-organic frameworks (MOFs) is expected to have a pronounced effect on the properties and performance of these materials. For instance, unexpected catalytic activity and adsorption behavior have been attributed to variations in defect density between MOF synthesis batches. However, current analytical techniques to detect framework degradation fall short. Bulk techniques such as XRD are more appropriate for monitoring drastic variations in crystallinity rather than subtle changes that leave most of the framework intact. Microscopic techniques (SEM, AFM) are better suited to identify the onset of degradation on the single crystal level but are limited to the outer surface of MOF crystals. We will present how the use of fluorescence microscopy enables a more detailed understanding of defect formation, including in the crystal interior. In the case of the MOF material HKUST-1, this method reveals the formation of defects along well-defined crystal planes when optimal synthesis time is exceeded, without observable changes in the XRD pattern. The three-dimensional capabilities of the presented technique allow measuring the angles between defect planes and unambiguously identifying them as {111} planes. Figure 1: Three-dimensional visualization of defects within a single HKUST-1 crystal. (a) 3D model based on fluorescence data. (b) XY-image slice as recorded. (c) XZ-image slice extracted from 3D model in (a).Reference: R. Ameloot, J. Hofkens, F. De Schryver, D. E. De Vos, M. B. J. Roeffaers, Angew. Chem. Int. Ed. 2013  , 52, 401-405. (Highlighted in Nature, 2013 , 493, 313: Defects visualized in porous solids)

Fluorescence microscopy-based 3D visualization of early stage defects in metal-organic frameworks

248th National Meeting (2014)

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