1,721,050 research outputs found
Synthesis and physico-chemical characterization of porous silica membranes obtained by using PS-b-PEO block copolymers as soft templating agents
No full textHighly selective membranes with controlled porosity can be obtained by growing thin films of mesoporous oxides on an appropriate support. This can be achieved employing organic/inorganic mixed micellar solutions based on the use of commercial or ad hoc designed templates. Amphiphilic block copolymers are very attractive materials as soft-templating agents. When mixed with organic solvents selective for one of the blocks, they can self-assemble into micelles with the insoluble blocks constituting the micellar core and the soluble ones the corona. The morphology and size of self-assembled micelles depend on the size (length) and nature (polarity) of the blocks, and on solution parameters. Silica porous membranes described in this contribution were obtained by sol-gel reaction of a silicon oxide precursor (TEOS) and using polystyrene-block-poly(ethylene-oxide) (PS-b-PEO) block copolymers as templates. In order to modulate pore sizes and alignment of the final material, many different variables were changed: e.g. block copolymer chain length, block copolymer/TEOS ratio, type of solvents, solvent ratio and use of additives (i.e. polystyrene homopolymer). Aim of the present work is the preparation of silica membranes with narrow pore size distribution and high porosity to be applied in the field of microfluidic analyses and as selective gates in microchip-based technologies for separation, detection and dosing of molecular or ionic species, charged nanoparticles or biomolecule
Synthesis of mesoporous silica films by block copolymers micellization
No full textHighly selective silica membranes with controlled porosity can be obtained by employing organic/inorganic mixed micellar solutions based on the use of commercial templates. Amphiphilic block copolymers are very attractive materials as structure directing agents. When mixed with organic solvents selective for one of the blocks, they can self-assemble into micelles with the insoluble blocks constituting the micellar core. The morphology and size of self-assembled micelles depend on the size (length) and nature (polarity) of the templates blocks, and on solution parameters. Silica porous films described in this contribution are obtained by sol-gel reaction of tetraethyl orthosilicate (TEOS) using polystyrene-block-poly(ethylene-oxide) (PS-b-PEO) copolymers as templates. In order to modulate pore sizes and alignment in the final material, many different variables are changed: e.g., block copolymer chain length, block copolymer/TEOS ratio, solvents, hydrophilic/hydrophobic solvent ratio and use of additives (i.e. polystyrene homopolymer). To obtain an oxidic mesoporous membrane, the block copolymer/TEOS micellar solution is deposited on inorganic supports via spin-coating. The spin coating conditions used ensure fast evaporation of solvents, freezing in the solid state the micelles shape present in solution. Block copolymer micelles are finally removed by thermal degradation in air, leaving an amorphous porous material which can be applied in the field of microfluidics for separation, detection and dosing of molecules, ions, charged nanoparticles or biomolecule
Surface Characterization of Modified Aluminas. IV. Surface Hydration and Lewis Acidity of CeO2-Al2O3 Systems
No full textHydrophobic W10O324-/silica photocatalyst for toluene oxidation in water system
Full text linkA new photocatalyst (Na4W10O32/SiO2/BTESE) has been prepared by simultaneous hydrolysis of tetraethyl orthosilicate (TEOS) and 1,2-bis(triethoxysilyl)ethane (BTESE) in the presence of Na4W10O32.
This material is able to scavenge and accumulate significant amounts of toluene from water solutions saturated with the hydrocarbon. This is due to its large specific surface area, micro and mesoporosity, and,
above all, to the high hydrophobicity of its surface. Moreover, photoexcited Na4W10O32/SiO2/BTESE show savery strong oxidizing ability, allowing an almost complete mineralization of toluene to CO2 through the formation and reactivity of OH• radicals. Considering both the sorption capability and the photocatalytic activity, the efficiency of Na4W10O32/SiO2/BTESE is significantly higher than those of Na4W10O32/SiO2 and Na4W10O32dissolved in homogeneous solution. At the end of a cycle of reaction, Na4W10O32/SiO2/BTESE is reusable without any loss of activity opening to the development of new efficient and stable photocatalytic systems addressed to clean wastewater containing aromatic hydrocarbons
Surface chemical functionalities in bioactive glasses. The gas/solid adsorption of acetonitrile
No full textEffect of sulfation on the acid-base properties of tetragonal zirconia. A calorimetric and IR spectroscopic study
No full textCharacterization of sol-gel bioglasses with the use of simple model systems: a surface-chemistry approach
No full textMICROCALORIMETRIC AND IR-SPECTROSCOPIC STUDY OF THE ROOM TEMPERATURE ADSORPTION OF CO2 ON PURE AND SULPHATED T-ZRO2
No full textSalts as structure-directing agents: The hypersaline chemistry of aerogels
No full textBased on recent investigations, the use of inorganic salts is a new powerful route for obtaining high surface area mesoporous materiaIs in a facile one-step approach, also called “salt-templating”.
Here, high surface area aerogels were synthesized adding simple inorganic water soluble salts as pore forming agents during the sol-gel process. The model oxide precursor (i.e.,TEOS for silica) hydrolyses in the presence of a salt, e.g. ZnCl2, without using any acid/base catalysts, forming the silica network and producing monoliths with high surface area. The porosity can be controlled by the gel-ageing step (the less the time, the higher the porosity). Two different gel-drying conditions were investigated: room temperature (RT) air drying and CO2 supercritical drying. Supercritically dried silica aerogels reach the impressive BET surface area value of ca. 1400 m2 g-1, but also the simple air-drying procedure produces highly porous monoliths with BET surface areas in the range of 700-800 m2 g-1, thanks to the stabilizing salting-in effect of zinc ions (according to Hofmeister series).
Compared to standard sol-gel processes, the herein presented synthesis is extremely simple: it only consists of dissolution of both oxidic precursors and inorganic salts in the selected solvent (i.e. ethanol), gel formation induced by solvent evaporation, salt removal through simple washing with water/ethanol. This way, no organic templates need to be employed and the overall approach is highly efficient and sustainable. In this regard, the salt-templating solution could principally be recovered for following syntheses afterwards, thus reducing by-products. Moreover, the synthesis of highly porous monoliths by RT air drying is of high interest since no special equipment is required, it simplifies the standard procedure and gives access to advanced materials at low cost
Epoxidation of Substitued Olefins with Hydrogen Peroxide Catalyzed by Mesoporous Tungsten Oxide - Silica Catalysts
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