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Silica Framework (silica + framework)
Selected AbstractsHeteropolyacid Encapsulated into Mesoporous Silica Framework for an Efficient Preparation of 1,1-Diacetates from Aldehydes under a Solvent-Free Condition.CHEMINFORM, Issue 9 2007Jianmin Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Templated Synthesis of Mesoporous Superparamagnetic Polymers,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007B. Fuertes Abstract We present a novel synthetic strategy for fabricating superparamagnetic nanoparticles randomly dispersed in a mesoporous polymeric matrix. This method is based on the use of mesoporous silica materials as templates. The procedure used to obtain these mesoporous magnetic polymers consisted in: a),generating iron oxide ferrite magnetic nanoparticles (FMNP) of size ,,7,8,nm within the pores of the silica, b),loading the porosity of the silica/FMNP composite with a polymer (Polydivinylbenzene), c),selectively removing the silica framework from the resulting silica/FMNP/polymer composite. Such magnetic porous polymeric materials exhibit large surface areas (up to 630,m2,g,1), high pore volumes (up to 0.73,cm3,g,1) and a porosity made up of mesopores. In this way, it is possible to obtain superparamagnetic mesoporous hybrid nanocomposites that are easily manipulated by an external magnetic field and display different magnetic behaviours depending on the textural properties of the template employed. [source] A quantitative morphological analysis of nanostructured ceria,silica composite catalystsJOURNAL OF MICROSCOPY, Issue 2 2008M. MOREAUD Summary This study aims at examining the morphology of different catalysts, which are based on a dispersion of ceria nanoparticles embedded in a high surface area mesoporous silica framework. In order to fully describe the mesostructured composite material, we propose here a quantitative description of the microstructure based on a quantitative analysis of micrographs that were obtained via high-resolution transmission electron microscopy. We have therefore developed an automatic image analysis process in order to automatically and efficiently extract all the components of the catalyst images. A statistical and a morphological analysis of the spatial arrangement of the components of the catalyst are also presented. The study shows clear differences between the materials analysed in terms of the spatial arrangement and the total surface area of the ceria phase emerging into the pores, parameters of prime importance for the catalytic properties. Thus, the silica,ceria nanostructured composite materials, displaying large surface area up to 300 m2 g,1 are shown to exhibit highly rugged surfaces resulting from ceria nanoparticles emerging in the pores. [source] Selective Adsorption of Polychlorinated Dibenzo- p -dioxins and Dibenzofurans by the Zeosils UTD-1, SSZ-24, and ITQ-4CHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2004Ralph Jäger Dr. Abstract Zeosils are microporous solids with a pure silica framework. Due to their hydrophobic properties, zeosils are ideal host materials for the adsorption of hydrophobic guest molecules. We tested zeosils with different pore diameters (UTD-1, SSZ-24 and ITQ-4 as well as CIT-5) for the selective adsorption of the polychlorinated dibenzo- p -dioxins and dibenzofurans. This group of highly toxic substances contains 210 congeners that possess similar chemical properties, but differ in their size and shape. In the experiment, polychlorinated dibenzo- p -dioxins and dibenzofurans were extracted from fly ash of a waste incinerator, adsorbed on amorphous silica, then thermally desorbed and flushed over a sequential arrangement of the zeosils at elevated temperature by a stream of nitrogen. ITQ-4 with the smallest pore diameter was placed first, followed by SSZ-24 and, finally, by UTD-1 with the largest pore diameter. After the experiment, the zeosils were analysed for their contents of the different congeners. The results show that the sorption of the congeners occurs selectively and that it is governed by the size and the shape of the dioxin molecules, which in turn depend on the number of chlorine atoms and the pattern of chlorine substitution (regioisomers). Geometrical reasoning as well as molecular dynamics calculations on the zeosil structures and on the dioxin molecules were helpful in rationalising the results. This work represents an especially complex case of the molecular sieving effect and may lead to a selective on-line monitoring of the concentrations of dioxin molecules in waste gases of industrial combustion processes. The size- and shape-selective sorption of dioxin molecules may also bear some resemblance to the molecular recognition process that occurs in nature at the aryl hydrocarbon receptor. [source] | ||||||||||