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Composite polyimide-silica materials have been synthesized via the sol-gel process and their gas transport properties studied. Structural characterizations have been performed showing that materials prepared with large concentration of silicon alkoxyde are composites made of silica particles embedded in the polyimide matrix while low-silicon alkoxyde concentration induces homogeneous materials. X-ray diffraction shows that the presence of silicon species induces modifications in the microstructure of the polyimide chains. These modifications have been confirmed by a shift of the glass transition temperature and density variations. Influence of the temperature and silicon species on the gas transport have been studied using various gases (nitrogen, oxygen, carbon dioxide, and methane) showing that gas permeation coefficients increase with the silicon species proportion. CO 2 sorption measurements have been performed at various temperatures and the results have been analyzed in terms of the dual sorption theory. Activation energies have been calculated for the permeation and sorption mechanisms. These results show that silicon species contributes to the overall permeability.

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This paper reports on the physicochemical reorganizations, at 40°C, of a template-free aluminosilicate system yielding an LTA-type zeolite. The events that take place in the system during the transformations of the amorphous material into a crystalline material were monitored by various characterization techniques which provide information from the molecular to the micrometer scale. High-resolution solid-state 29 Si and 27 Al MAS NMR spectroscopy, small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used in order to achieve a better understanding of the structural properties of the precursor gel and its transformation into a crystalline zeolite-type material. The experimental results show that the first crystallization stage

The performance of bulk materials often depends on the size and habit of the primary particles, and their ordering into hierarchical structures. In the area of catalysis and separation processes, ordered materials with well-defined periodic structures and controlled sizes are highly desired. Hierarchical porous structures combine the benefits of each pore-size regime and are expected to lead to higher efficiency and new applications in catalytic and separation processes, biomolecular separations, and chromatographic supports. [1] The most commonly used approach for the fabrication of such materials is the application of sacrificial templates, which after the synthesis of the inorganic framework are dissolved or volatilized by heating. The template approach, first employed for the preparation of zeolite-type materials, where small organic molecules are used for directing the microporosity, [2] was extended to the formation of mesoporous [3] and macroporous [4] structures. By employing dual templates, hierarchical porous materials with combinations of micro-/meso-[*] Dr.

The preparation of core/shell nanoparticles that enable ratiometric pH measurement is described. The core of the nanoparticles consists of a zeolite‐β matrix that exhibits a 3‐hydroxyflavone reference dye within the porous network. Coating an amorphous silica shell containing a fluorosensor around the zeolite through the Stöber process provides pH sensitivity to the nanoparticles. Morphological characterization (dynamic light scattering, transmission electronic microscopy) demonstrates the control of the sensing silica shell around the zeolite cores, leading to highly monodisperse spherical nanoparticles, while structural characterization (wide‐angle X‐ray diffraction, nitrogen adsorption) shows the amorphous character of the shell. Spectral characterization via UV/Vis absorption and steady‐state fluorescence shows good pH sensitivity of the resulting nanosensors with a pKa suitable for bioanalytical applications.

Biomimetic zeolite Beta macrostructures with hierarchical porosity were prepared by using a silica-containing vegetal template (Equisetum arvense). Leaves and stems of Equisetum arvense were subjected to hydrothermal treatment with a zeolite Beta precursor solution. The zeolite readily crystallized in the vegetal tissues with the zeolite nucleation being induced by the highly reactive biomorphic silica deposited at the epidermal surface of the plant. Upon calcination the obtained zeolite/vegetal composite was transformed into a solely zeolite macrostructure that retained all morphological features of the vegetal template. The analysis of the zeolite/vegetal composite and all-zeolite replica showed that material with hierarchical porosity was obtained. The leaves and the stems of Equisetum arvense were transformed into micro-/mesoporous and micro-/meso-/macroporous structures, respectively. These structures were built up of zeolite nanoparticles with smaller sizes compared to the crystals from the bulk solution. Thus, the biotemplate controlled both the macromorphology and the nanolevel organization of the materials.

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