High-resolution transmission electron adsorption

The mesoporosity of these materials has been established by BET measurements and gas adsorption experiments. As the chain length of the surfactant was increased from Cs to G 5, the amount of adsorbed benzene was increased, indicating that there was a relationship between the size of the surfactant and the amount of gas adsorbent taken up by the MCM-41 material. In terms of a comparison to zeolite materials, experiments were done at 60 torr pressure and at 25< C. llie US-Y zeolite sample had an uptake that was about 4 times less than that of MCM-41. The above mentioned MCM-41 materials all show pore size distributions with broad bands centered around 40 A. The pore size distribution measurements are a true indication of the size of the pores and can be used to verify the existence of mesopores. Further evidence of mesoporosity comes from X-ray powder difraction experiments which were done to determine the crystallinity of these materials. The position of the (100) reflection was found to correlate with the amount of uptake by the different materials, or in therwords, with the mesoporosity of these systems. Pores of the MCM-41 materials were shown to form in a hexagonal shape by using high resolution transmission electron microscopy data. 10... 

High resolution transmission electron microscopy examinations were performed on catalyst particles that have treated at temperatures in excess of 725°C in the presence of CO/H2. Most of the bimetallic particles had short filaments associated with them, indicating that under these conditions the catalytic activity towards the growth of this form of carbon was relatively low. It was significant, however, to find that the particle surfaces on which gas phase adsorption and decomposition reactions occurred had remained completely free of any accumulated carbon residues. This observation is consistent with the argument that the... 

Except for the fullerenes, carbon nanotubes, nanohoms, and schwarzites, porous carbons are usually disordered materials, and cannot at present be completely characterized experimentally. Methods such as X-ray and neutron scattering and high-resolution transmission electron microscopy (HRTEM) give partial structural information, but are not yet able to provide a complete description of the atomic structure. Nevertheless, atomistic models of carbons are needed in order to interpret experimental characterization data (adsorption isotherms, heats of adsorption, etc.). They are also a necessary ingredient of any theory or molecular simulation for the prediction of the behavior of adsorbed phases within carbons - including diffusion, adsorption, heat effects, phase transitions, and chemical reactivity. 

The gold content in catalysts was analyzed by Atomic absorption method and made by the Analytical Center of the CNRS, Lyon, France. The XRD patterns were obtained with a Philips PW 170 diffiactometer, using Cu Ka (1.54178 A) radiation. High resolution transmission electron microscopy (HRTEM) analysis was performed on a Jeol JEM-3010 microscope at 300 kV. Nitrogen adsorption-desorption isotherms and specific surface areas were measured at -196 °C over a wide relative pressure range from 0.01 to 0.995 with a volumetric adsorption analyzer TRISTAR 3000 manufactured by Micromeritics. The pore diameter and the pore size distribution were determined by the Barret-Joyner-Halenda (BJH) method using the adsorption branch of isotherms [15]. 

We chose to study the adsorption of plasma proteins to surfaces by using high resolution transmission electron microscopy. This allowed us to assess conformational changes of the protein molecules due to the specific surface to which they are adsorbed, and to examine surfaces following initial protein adsorption. Utilizing this technique, we have been able to observe individual molecules as well as the structure of the protein films adsorbed to these surfaces. 

Figures 1 and 2 illustrate two key signatures of wholly microporous silicon the absence of any mesopores (>2 nm width) by high-resolution transmission electron microscopy (see handbook chapter Microscopy of Porous Silicon ) and the absence of any hysteresis in a type I isotherm of nitrogen adsorption and desorption in a material of very high surface area (see handbook chapter Gas Adsorption Analysis of Porous Silicon ).

The micropore structure can be determined by several methods such as immersion calorimetry, small-angle X-ray scattering (SAXS) high resolution transmission electron microscopy (HRTEM) and s- and liquid-phase adsorption, among which the most widely us is gas adsorption[7]. The pore structure of activated carbon is usually characterised in terms of the pore size distribution (PSD), perhaps die most imporlant aspect of characterization of die structural heterogeneity of porous solids used in industrial applications. This PSD could be obtained as an arbitrarily chosen form such as, for instance, mma or C ssian distribution[8]. For a local isodierm one may choose traditional mmlels, statistical mechanical methods such as DFT, or, most accurate for micropores, methods based on Monte Carlo simulation. 

Kuo and Lu coated the surfaces of the spherical voids with 10-15 nm TiOi nanoparticles by TiCU treatment to increase the surface area for dye adsorption. Figure 3.43 shows the SEM and high resolution transmission electron microscopy (HRTEM) images of the structures. The voids were 100 nm in diameter with transport channels of 30-50 nm in between. The film was 25 pm in thickness. The Voc decay when switching from AM 1.5 to dark was recorded for a 13 pm film and the calculated. The inverse opal structure was found to result in longer... 

When one is asked to describe porosity, using paper and pencil, first attempts are as seen in Chapter 3, as Figures 3.1-3.3. The approach of textbooks when describing adsorption in porous solids is the thermodynamics of adsorption processes. Although high-resolution transmission and scanning electron microscopy (HRTEM and SEM, respectively) have been available for at least 20 years, this facility has probably been under-exploited in analysis of structure in activated carbons. 

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). 

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