Nanostructured materials transmission electron microscopy

For the detailed study of reaction-transport interactions in the porous catalytic layer, the spatially 3D model computer-reconstructed washcoat section can be employed (Koci et al., 2006, 2007a). The structure of porous catalyst support is controlled in the course of washcoat preparation on two levels (i) the level of macropores, influenced by mixing of wet supporting material particles with different sizes followed by specific thermal treatment and (ii) the level of meso-/ micropores, determined by the internal nanostructure of the used materials (e.g. alumina, zeolites) and sizes of noble metal crystallites. Information about the porous structure (pore size distribution, typical sizes of particles, etc.) on the micro- and nanoscale levels can be obtained from scanning electron microscopy (SEM), transmission electron microscopy ( ), or other high-resolution imaging techniques in combination with mercury porosimetry and BET adsorption isotherm data. This information can be used in computer reconstruction of porous catalytic medium. In the reconstructed catalyst, transport (diffusion, permeation, heat conduction) and combined reaction-transport processes can be simulated on detailed level (Kosek et al., 2005). 

Thus far, we have defined nomenclature for amorphous OD nanostructures. Analogous to bulk materials, any nanomaterial that is crystalline should be referred to as a nanocrystal. This term should be reserved for those materials that are singlecrystalline if a particle exhibits only regions of crystallinity, it is better termed a nanoparticle or nanocluster depending on its dimensions. Transmission electron microscopy, especially in tandem with electron diffraction is most useful in determining the crystallinity of any nanostructure (Figure 6.8). 

To understand the importance of nanostructures in microsieving membranes, the basic structure of nanophased ceramics must be briefly described. Because the particles are extremely small, one to a few tens of nanometers, an important fraction of the atoms is found in or very near the interface between grains, as reported in Table 2 [32]. Figure 11 is a schematic representation of a nanophase material. One can see that individual grains in the 5 nm range induce a biphasic material with an interfacial phase between the grains and a residual nanoporosity, evidenced by positron lifetime spectroscopy [33]. Transmission electron microscopy is also a well-adapted technique for nanoscale structure characterization, as illustrated later. 

For the comprehension of mechanisms involved in the appearance of novel properties in polymer-emhedded metal nanostructures, their characterization represents the fundamental starting point. The microstructural characterization of nanohllers and nanocomposite materials is performed mainly by transmission electron microscopy (TEM), large-angle X-ray diffraction (XRD), and optical spectroscopy (UV-Vis). These three techniques are very effective in determining particle morphology, crystal structure, composition, and particle size. 

Transmission electron microscopy (TEM) This technique is used when the MPCM is in nanometer size range. The specimen must have a low density, allowing the electrons to travel through the sample. There are different ways to prepare the material it can be cut in very thin slices either by fixing it in plastic or working with it as frozen material. Pan et al. studied nanostructures that were prepared through the methodology in-situ interfacial polycondensation. 

A cross-sectional transmission electron microscopy (TEM) image of a material with predetermined morphology of spherical pores was examined. The structure consists of an interfacial layer, structural layer, and a substrate. The substrate is in direct mechanical contact with the interfacial layer. The structural layer is composed of spherical nanopores nanostructure, and essentially consists of the cross-linkable polymer. The interfacial layer lacks the spherical nanopores. The thickness of the interfacial layer is 2-30 nm. The structural layer thickness is of the range 50-300 nm. 

X-ray diffraction technique is a non-destructive analytical technique that reveals information about crystallographic structure, chemical composition and physical properties of nanostructured materials. UV/Vis spectroscopy is routinely used in the quantitative determination of films of nanostructured metal oxides. The size, shape (nanocomb and nanorods etc,) and arrangement of the nanoparticles can be observed through transmission electron microscope (TEM) studies. Surface morphology of nanostructured metal oxides can be observed in atomic force microscopy (AFM) and scanning electron microscopy (SEM) studies. 

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