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Metal-organic frameworks (MOFs) feature a great possibility for a broad spectrum of applications. Hollow MOF structures with tunable porosity and multifunctionality at the nanoscale with beneficial properties are desired as hosts for catalytically active species. Herein, we demonstrate the formation of well-defined hollow Zn/Co-based zeolitic imidazolate frameworks (ZIFs) by use of epitaxial growth of Zn-MOF (ZIF-8) on preformed Co-MOF (ZIF-67) nanocrystals that involve in situ self-sacrifice/excavation of the Co-MOF. Moreover, any type of metal nanoparticles can be accommodated in Zn/Co-ZIF shells to generate yolk-shell metal@ZIF structures. Transmission electron microscopy and tomography studies revealed the inclusion of these nanoparticles within hollow Zn/Co-ZIF with dominance of the Zn-MOF as shell. Our findings lead to a generalization of such hollow systems that are working effectively to other types of ZIFs.

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Iron oxide nanoparticles were prepared using the simplest and most efficient chemical route, the coprecipitation, in the absence and the presence of three different and widely used surfactants. The purpose of this study is to investigate the possible influence of the different surfactants on the structure and therefore on the magnetic properties of the iron oxide nanoparticles. Thus, different techniques were employed in order to elucidate the composition and structure of the magnetic iron oxide nanoparticles. By combining transmission electron microscopy with X-ray powder diffraction and X-ray absorption fine structure measurements, we were able to determine and confirm the crystal structure of the constituent iron oxides. The magnetic properties were investigated by measuring the hysteresis loops where the surfactant influence on their collective magnetic behavior and subsequent AC magnetic hyperthermia response is apparent. The results indicate that the produced iron oxide nanoparticles may be considered as good candidates for biomedical applications in hyperthermia treatments because of their high heating capacity exhibited under an alternating magnetic field, which is sufficient to provoke damage to the cancer cells.

382 wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com MIL-101 giant-pore metal-organic framework (MOF) materials have been loaded with Pt nanoparticles using atomic layer deposition. The fi nal structure has been investigated by aberration-corrected annular dark-fi eld scanning transmission electron microscopy under strictly controlled lowdose conditions. By combining the acquired experimental data with image simulations, the position of the small clusters within the individual pores of a metal-organic framework has been determined. The embedding of the Pt nanoparticles is confi rmed by electron tomography, which shows a distinct ordering of the highly uniform Pt nanoparticles. The results show that atomic layer deposition is particularly well-suited for the deposition of individual nanoparticles inside MOF framework pores and that, upon proper regulation of the incident electron dose, annular dark-fi eld scanning transmission electron microscopy is a powerful tool for the characterization of this type of materials at a local scale.of MOFs have focused lots of attention to these materials, with the main applications lying in the fi eld of catalysis, [5][6][7] gas storage and separation, [ 3,8,9 ] and drug delivery. [10][11][12] The tunable pore size can also be used as a template for confi ned growth of metal or metal-oxide nanoparticles with sizes tailored to the MOF pore diameter, [ 13,14 ] e.g., catalytic applications. Over the past decade, numerous approaches have been investigated for the embedding of nanoparticles within MOFs. [ 15 ] Besides the typically used liquid impregnation and solid grinding, postsynthetic metalation from the vapor-phase is a widely used method. [ 15 ] However, this technique provides little control over the spatial distribution of the species within the framework. Atomic layer deposition (ALD) is a powerful technique that allows controlled gas phase deposition of metal oxide monolayers on the surface of ordered mesoporous materials. [16][17][18][19][20][21] An ALD process typically consists of alternating precursor (A) and reactant gas (B) pulses, i.e., cyclic AB-type exposures that allow to deposit material with atomic precision in a conformal way. Owing to its lower working temperature in comparison to chemical vapor deposition, ALD can be applied to samples with a reduced stability. [22][23][24] Of pivotal importance in controlling and refi ning MOF material properties during synthesis is the possibility to characterize them at a local scale. Transmission electron microscopy (TEM) is a powerful tool in order to extract information on the atomic scale for both empty and loaded metal-organic frameworks. [ 5,6,14,[25][26][27][28][29] In the past, techniques like electron diffraction [ 25,26 ] bright-fi eld TEM, [ 13,15,30 ] high-angle annular dark-fi eld scanning transmission electron microscopy (HAADF-STEM), [ 31 ] and electron tomography [ 13,32 ] have been used to great effect to retrieve morphological and structural information on MOFs and nanoparticle-loade...