Direct Imaging of Loaded Metal−Organic Framework Materials (Metal@MOF-5)

Abstract

We illustrate the potential of advanced transmission electron microscopy for the characterization of a new class of soft porous materials: metal@Zn4O(bdc)3 (metal@MOF-5; bdc = 1,4-benzenedicarboxylate). By combining several electron microscopy techniques (transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and electron tomography) and by carefully reducing the electron dose to avoid beam damage, it is possible to simultaneously characterize the MOF-5 framework material and the loaded metal nanoparticles. We also demonstrate that electron tomography can be used to accurately determine the position and distribution of the particles within the MOF-5 framework. To demonstrate the implementation of these microscopy techniques and what kind of results can be expected, measurements on gas-phase-loaded metal−organic framework materials Ru@MOF-5 and Pd@MOF-5 are presented.

Selectivity in sorption and hydrogenation of methyl oleate and elaidate on MFI zeolites

“…The HAADF inner collection semi-angle was 90 mrad. For all techniques, low-intensity beam conditions (lowest possible magnification, low beam intensity and long exposure times) were used as much as possible to minimize the electron dose and possible beam damage of the supported metal particles [28]. The images for the tomographic acquisition were taken in bright-field TEM instead of the HAADF-STEM mode.…”

“…Although unwanted diffraction contrast inevitably occurs with this technique, use of bright-field TEM was required for the tomography images as prolonged STEM illumination can damage soft porous materials [28].…”

Synthesis and applications of metal-organic framework–quantum dot (QD@MOF) composites

“…[52,54,62] However, QDs often have a low contrast compared with metallic nanoparticles; thus, to provide an average of the QD size can be challenging from microscopy images alone. Nevertheless, in some cases it is possible to circumvent this problem and estimate the size of the QD from the main peak of the absorption band (exciton peak), as reported by Peng et al in the case of CdSe QDs.…”

“…It should be noted that bottom-up strategies to prepare QDs often rely on relatively harsh reaction conditions which can lead to local network degradation as reported for the deposition of metallic NPs into MOF matrices using this method. [54] For QDs, the MOF matrix needs to be particularly stable under high temperatures (in some cases heat treatments can exceed 300 o C) and/or redox environments; if framework-forming metal ions are susceptible to changes in oxidation state this could lead to network degradation. As previously highlighted, further consideration of this synthetic route to access MOF@QD composites, regards the location and distribution of the QDs within the pores of the framework which could potentially decrease the surface area of the MOF matrix strongly impacting on those applications where porosity is important.…”

Ein Meilenstein in der Strukturaufklärung nanoporöser Festkörper: Kombination dreier komplementärer Methoden

“…[5b] kçnnen hilfreich sein und außerdem eine robuste quantitative Behandlung [5a,b] der 3D-Strukturdaten erlauben), [4,13] dennoch ist das Potential des von GarciaMartinez et al [1] beschriebenen Ansatzes enorm. …”