Gradual hydrophobic surface functionalization of dry silica aerogels by reaction with silane precursors dissolved in supercritical carbon dioxide

Sanz-Moral, Luis Miguel; Rueda, Miriam; Nieto, Antonio; Novak, Zoran; Knez, Željko; Martín, Ángel

doi:10.1016/j.supflu.2013.09.010

Cited by 35 publications

(16 citation statements)

References 16 publications

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“…catalysts. The untreated support shows some methyl groups on the surface (815, 2862, 2936 and 2974cm -1 ); these groups are expected to correspond to residual nonhydrolyzed alkoxy groups on the surface of the silica aerogels [18]. The free metal support was also reduced under the same conditions which were used to reduce the catalysts and not important fluctuations where noticed on the spectra.…”

Section: Infrared Spectra Studiesmentioning

confidence: 98%

Tuned Pd/SiO 2 aerogel catalyst prepared by different synthesis techniques

Sanz-Moral

Romero

Holz

et al. 2016

Journal of the Taiwan Institute of Chemical Engineers

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Pd nanoparticles have been embedded on silica aerogel by using three different techniques. In each of them the metal was loaded in the matrix at different steps of the production: the direct synthesis, the wet impregnation and the supercritical impregnation of the previously dried aerogels. The resultant materials have been characterized to analyze the differences depending on the applied technique for its impregnation. Atomic absorption, nitrogen physisorption, X-ray diffraction, infrared spectroscopy and transmission electron microscopy where performed. In all the techniques the concentration of metal has been varied (from 0.13 to 1.61 % wt.) by modifying the concentration of the suspension (Pd-polyvinylpyrrolidone nanoparticles used in the direct synthesis) or of the solution of the metallic precursor (palladium acetylacetonate), both in the organic solvent and the supercritical media. The characterization had generally shown a good distribution of the metallic particles in the matrix, and the negligible effect of the metal on the textural properties. Finally, considerable variations where observed on the silanol groups on the surface of the catalysts. These materials were tested in D-glucose hydrogenation, observing significant differences on the performance of the catalyst depending on the synthesis technique employed.

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Section: Infrared Spectra Studiesmentioning

confidence: 98%

Tuned Pd/SiO 2 aerogel catalyst prepared by different synthesis techniques

Sanz-Moral

Romero

Holz

et al. 2016

Journal of the Taiwan Institute of Chemical Engineers

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“…The very intense and broad band appearing at 1050 cm −1 and the shoulder at around 1200 cm −1 are respectively assigned to the transversal optical and longitudinal optical modes of the Si-O-Si asymmetric stretching vibrations. On the other hand, the symmetric stretching vibrations of Si-O-Si appear at 800 cm −1 [31]. The strong band at 1569 cm -1 stems from the aromatic C=C stretching vibrations of the carbons [32].…”

Section: Numerical Simulation and Vessel Designmentioning

confidence: 99%

Release of hydrogen from nanoconfined hydrides by application of microwaves

Sanz-Moral

Navarrete

Sturm

et al. 2017

Journal of Power Sources

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The release of hydrogen from solid hydrides by thermolysis can be improved by nanoconfinement of the hydride in a suitable micro/mesoporous support, but the slow heat transfer by conduction through the support can be a limitation. In this work, a C/SiO 2 mesoporous material has been synthesized and employed as matrix for nanoconfinement of hydrides. The matrix showed high surface area and pore volume (386 m²/g and 1.41 cm³/g), which enabled the confinement of high concentrations of hydride. Furthermore, by modification of the proportion between C and SiO 2 , the dielectric properties of the complex could be modified, making it susceptible to microwave heating. As with this heating method the entire sample is heated simultaneously, the heat transfer resistances associated to conduction were eliminated. To demonstrate this possibility, ethane 1,2diaminoborane (EDAB) was embedded on the C/SiO 2 matrix at concentrations ranging from 11 to 31%wt using a wet impregnation method, and a device appropriate for hydrogen release from this material by application of microwaves was designed with the aid of a numerical simulation. Hydrogen liberation tests by conventional heating and microwaves were compared, showing that by microwave heating hydrogen release can be initiated and stopped in shorter times.

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“…The silica aerogel can then be obtained by a supercritical drying process with carbon dioxide (CO 2 ) ,. However, the alkoxide‐derived silica aerogels use expensive precursors, and the supercritical drying process requires long processing times (low heating and depressurization rates), which increases the overall cost of the aerogel.…”

Section: Figurementioning

confidence: 99%

Fast Synthesis of Spherical Silica Aerogel Powders by Emulsion Polymerization from Water Glass

Lee

Kim²,

Lee³

et al. 2018

ChemistrySelect

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In this study, a fast synthesis technique for silica aerogel powder was proposed that reduces the length of the tedious surface modification and solvent exchange processes. Spherical silica aerogel powder could be fabricated by an emulsion polymerization method from water glass and n-hexane. A stable water glass-in-hexane emulsion with a water glass to hexane ratio of 5:5 was fabricated using the surfactant, sorbitan monooleate (Span80). It was found that acetic acid and isopropanol catalysts for the hydrolysis and condensation of water glass droplets dispersed in the emulsion were crucial for the synthesis of the spherical silica aerogel powder with a narrow particle size distribution and for reducing production time. In addition, the particle size of the spherical silica aerogel could be controlled by changing the water glass droplet size.A silica (SiO 2 ) aerogel is an ultra-porous (90-99% of theoretical density) material with a 3-dimensional network structure of silica nanoparticles. [1] Because of its interesting characteristics such as high specific surface area, low thermal conductivity, low dielectric constant, and low refractive index, it has received wide attention within various fields as a promising material for catalysis, [2,3] adsorption, [4,5] heat insulation [6,7] and drug delivery. [8"9] Silica aerogels are normally synthesized via a sol-gel route from silicon alkoxides such as tetramethylorthosilicate (TMOS) or tetraethylorthosilicate (TEOS). A silica wet gel is formed as a result of a hydrolysis and condensation process of the silicon alkoxide molecules. The silica aerogel can then be obtained by a supercritical drying process with carbon dioxide (CO 2 ). [10,11] However, the alkoxide-derived silica aerogels use expensive precursors, and the supercritical drying process requires long processing times (low heating and depressurization rates) [12,13] which increases the overall cost of the aerogel.Ambient pressure drying (APD) is another option to produce silica aerogel, and water glass-based silica aerogels by APD has been extensively studied by many researchers. [14][15][16][17] The APD relies on surface modification and solvent exchange processes that are not only tedious but also economically unfavorable. Since surface modification agents (typically, trimethylchlorosilane (TMCS) or hexamethyldisilazane (HMDS)) can be transported within the silica hydrogel only by diffusion, APD requires processing times longer than a few or sometimes even tens of hours. [14][15][16] Recently, some groups have attempted to reduce the processing time of APD via a co-precursor method. [18][19][20] Huber et al. proposed a one-pot synthesis technique for a silica aerogel granulate, which could reduce solvent use and production time to within 4 h. However, they used an expensive precursor like polyethoxysiloxane (PEDS), and the morphology of the synthesized silica aerogel granulate was irregular. [21] Pan et al. prepared a silica aerogel powder via APD from water glass within 4 h. [22] Although the mechanical cru...

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Gradual hydrophobic surface functionalization of dry silica aerogels by reaction with silane precursors dissolved in supercritical carbon dioxide

Cited by 35 publications

References 16 publications

Tuned Pd/SiO 2 aerogel catalyst prepared by different synthesis techniques

Tuned Pd/SiO 2 aerogel catalyst prepared by different synthesis techniques

Release of hydrogen from nanoconfined hydrides by application of microwaves

Fast Synthesis of Spherical Silica Aerogel Powders by Emulsion Polymerization from Water Glass

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