Abstract
AbstractThe first example of layer‐by‐layer growth of a metal–organic framework (MOF) directly on transmission electron microscopy (TEM) grids is described. ZIF‐8 is deposited on thin amorphous carbon films and subjected to a structure analysis by (scanning) TEM ((S)TEM). This method serves as a two‐in‐one synthesis and TEM sample‐preparation technique and allows straightforward analysis of ZIF‐8 crystallites. Artifacts resulting from sample preparation are completely avoided by this approach. The morphological properties, crystal structure, and the chemical composition of the material are investigated with high spatial resolution by a variety of methods of (analytical) electron microscopy. Furthermore, the incorporation of metallic nanoparticles in ZIF‐8 by integrating a corresponding step into the layer‐by‐layer deposition process is examined. The formation of ZIF‐8 crystals on the film proceeds as under the absence of nanoparticle‐forming synthesis steps. However, the nanoparticles rather cover the supporting amorphous carbon film than being incorporated in the ZIF‐8 material. This information cannot be obtained from standard characterization techniques but requires the application of analytical (S)TEM techniques.
Highlights
Zeolitic imidazolate frameworks (ZIFs)-8 is deposited on thin amorphous carbon films and subjected to a structure analysis by Transmission electron microscopy (TEM) ((S)TEM)
We report the successful lbl growth of ZIF-8 on commercially available TEM grids, which consist of a thin amorphous carbon film supported by a Cu grid
An amorphous carbon (aC)-covered TEM grid freshly modified by UV/ozone plasma was immersed in those solutions, with rinsing steps in pure MeOH in between (Scheme 2a)
Summary
ZIF-8 in the form of SURMOF was synthesized directly on the aC-covered TEM grid by the lbl method, similar to the previously reported technique.[22,23] We note that the term lbl does not imply planar growth, where a closed ZIF-8 layer is formed from the start of the deposition. Since SURMOF-coated TEM grids are too small for direct investigation by powder X-ray diffraction (pXRD) and other standard characterization methods, macroscopic substrates with an OH terminated surface (11-mercapto-1-undecanol self-assembled monolayer (MUD SAM)), chemically comparable with that of the UV/ozone plasma-treated aC-covered. Besides the SURMOF growth on aC-covered TEM grids, macroscopic substrates were used for mNPs/ZIF-8 preparation. Some of the smaller particles are more rounded compared to the bigger ones This difference in the size and shape of ZIF-8 crystals after 50 deposition cycles indicates that during our lbl method ZIF-8 crystals pass through different growth stages, as it is reported for the powder ZIF-8 synthesis and discussed above.
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