Mesostructural effects

Similarly, Hg(n) binding to thiol-functionalized mesoporous silica for which effective access to all the binding sites (100% of SH groups com-plexed with Hg(n) was achieved in micelle-templated mesostructures with pore diameters larger than 2.0 nm, whereas incomplete filling was always observed with corresponding amorphous silica-based adsorbents.37... 

Support Effects from Surface-Modified Mesostructured Substrates... 

The catalyst layer is composed of multiple components, primarily Nafion ion-omer and carbon-supported catalyst particles. The composition governs the macro- and mesostructures of the CL, which in turn have a significant influence on the effective properties of the CL and consequently the overall fuel cell performance. There is a trade-off between ionomer and catalyst loadings for optimum performance. For example, increased Nafion ionomer confenf can improve proton conduction, but the porous channels for reactanf gas fransfer and water removal are reduced. On the other hand, increased Pt loading can enhance the electrochemical reaction rate, and also increase the catalyst layer thickness. 

A particularly interesting property of this mesostructured cubic Ge framework is the substantial blue-shift in optical absorption at 1.42 eV relative to 0.66 eV of bulk Ge. This large blue-shift can be understood by considering the change in the density of the electronic energy states caused by the substantial dimensional reduction of the Ge structure from the bulk Ge (infinity wall thickness) to an 1 nm. Similar large blue-shifted band gaps by 0.76 eV are also observed in Ge nanocrystals of 4 nm in diameter, which is a consequence of quantum confinement effects [42], Whether... 

Fig 1A shows the XRD pattern of the calcined MCM-41 sample synthesized from C,6TMAB-silica and aluminosilicate systems with the Si/Al = oo(sample I) and 37(sample II) by using the delayed neutralization process. In both materials, there exist at least 4 sharp XRD peaks, which indicate well-ordered hexagonal structure of MCM-41. It means that the incorporation of aluminum into silica framework could not have significant effect on the arrangement of MCM-41 mesostructure. When the nitrogen adsorption-desorption isotherms... 

Si MAS NMR spectra of the uncalcined MCM-41 samples synthesized normally and with TPA+ and Na+ are shown in Fig 4. It was observed that the ratio of Q4/Q3 peaks was higher in samples synthesized with additional cations. The effect was most pronounced with TPA" as the additional cation. The higher Q4/Q3 ratio indicates that the silicate polymerization during the formation of the mesostructure was enhanced by the presence of the additional cations, Upon calcination, the free silanol groups are forced to condense to form Si-O-Si bond and 29Si MAS NMR of the samples showed predominantly Q4 peak. However, these... 

However, solvent extraction has proven to be more effective. When a sample of 1 g MTS-W was dispersed in 50 mL of ethanol and refluxed for 12 hours. Elemental analysis showed that ca. 50% of the organic templates could be removed without any apparent effect on the stability of the mesostrucutre. We have also found that the mesostructured compounds are stable in concentrated HC1 solution. For example, when MTS-W was stirred in a 12M HC1 solution at room temperature for 12 hours, ca. 30% of the organic templates could be removed without collapsing the mesostructure or decomposing the inorganic walls. 

A novel mesoporous intercalate belonging to the class of mesostructured solid acids known as porous clay heterostructures (PCH) has been synthesized through the surfactant - directed assembly of silica in the two - dimensional galleries of saponite. The new saponite PCH, denoted SAP-PCH, exhibits a basal spacing of 32.9 A, a BET surface area of 850 m2/g and pore volume of 0.46 cm3/g. SAP-PCH is an effective catalyst for the condensed phase Friedel-Crafts alkylation of bulky 2,4-di-tert-butylphenol (DBP) with cinnamyl alcohol to produce a large flavan, namely, 6,8-di-tert-butyl-2,3-dihydro[4H]benzopyran. 

It is also possible to monitor the effect of the reaction time on the final mesostructured samples by in-situ SAXS. Figure 7 shows the time-resolved diffraction patterns of a 20 % w/w sample in ethanol at room temperature. The 001 reflection of the lamellar phase becomes more dominant in the course of time. Again, this is consistent with the relative compositions of the final mesostructured samples obtained from syntheses employing different reaction times. 

Figure 5.3.9 (A) Simplified geometric model [46, 89] for the preparation of industrial Cu/ZnO catalysts comprising subsequent meso- and nanostructuring of the material from [56], In a first micro structure directing step (mesostructuring), the Cu,Zn coprecipitate crystallizes in the form of thin needles of the zincian malachite precursor, (Cu,Zn)2(0H)C03. In a second step, the individual needles are decomposed and demix into CuO and ZnO. The effectiveness of this nanostructuring step depends critically on a high Zn content in the precursor, which in zincian malachite is limited to Cu Zn ca. 70 30 due to solid-state chemical constraints [75]. Finally, interdispersed CuO/ZnO is reduced to yield active Cu/ZnO. (B) Chemical memory Dependence of catalytic activity in methanol synthesis on the conditions of the coprecipitation and aging steps, from [85].

There have been only a few reports of mesostructured metal sulfides. Mesoporous cadmium sulfide was prepared from polyethylene oxide surfactants and cadmium salts exposed to hydrogen sulfide [35], A study of the effects of the counter-anion on the formation of CdS mesostructures led to the conclusion that the use of cadmium nitrate and perchlorate salts improved the degree of order of the mesostructure over the chloride, sulfate and acetate salts. This effect was attributed to the stronger acidity of conjugate acid by-products of the reaction in the case of nitrates that leads to the dissolution of high-energy defects and enhances structural order. 

Pure mesoporous silicas have little or no intrinsic catalytic activity, but catalytic centers can be introduced by grafting organic ligands onto the framework walls" or by incorporating metal ions into the framework12,13. Ti-functionalized derivatives are especially effective in demonstrating the importance of framework access in determining the catalytic activity of a mesostructure. 

The effect of PEG on thermal stability of the mesostructured Ce02 powders has been observed by comparing the difference of properties between the samples CPN-2 and CN. Figure 10 shows the small angle XRD patterns of the samples CPN-2 and CN. After calcination at 673K, the low-angle diffraction peak in the XRD pattern of CN disappeared, but still existed in that of CPN-2. This may be attributed to the thermal stability improvement deriving from non-ionic surfactant PEG. 

This paper presents an overview of the pore structural properties of different mesostructured materials prepared at room temperature, namely MCM-41, MCM-48 and MMS. The stability towards water vapour of some samples is inferred by XRD and nitrogen adsorption after and prior to water adsorption. It is shown that MMS materials are more stable than MCM-41. A new method for the stabilisation of MCM-41 using tetraethoxysilane (TEOS) in hexane as silicification agent is proposed and it is shown to be effective in stabilising the pore structure and to increase significantly the surface hydrophobicity. 

EFFECTS OF MESOSTRUCTURE ON CRACK GROWTH CONTROL CHARACTERISTICS IN Z-PINNED LAMINATES... 

Effects of Mesostructure on Crack Growth Control Characteristics... 

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