A Comparison of Tio<sub>2</sub>-Sio<sub>2</sub> Aerogels and Xerogels

Cogliati, G.; Guglielmi, Massimo; Che, Tao; Clark, Thomas J.

doi:10.1557/proc-180-329

Cited by 6 publications

(3 citation statements)

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“…In particular, the preparation of intimately mixed oxides with interesting structural and chemical properties require evenly matched precursor reactivities. This matching is achieved and preserved by the following concepts, either by themselves or in combination with each other: (i) chemical modification of the more reactive precursor, ,, (ii) nature of the precursor, ,, (iii) prehydrolysis of the less reactive precursor, ,− (iv) use of inorganic acids to decouple hydrolysis and condensation (fast hydrolysis relative to condensation), , (v) different sol−gel temperature, and (vi) different drying conditions. ,, Estimates of the SSG reactivity are derived from the so-called partial charge model 27 which is based on the principle of electronegativity equalization . Since the metal centers of transition-metal alkoxides possess much higher positive partial charges as well as electronegativity than silicon in corresponding alkoxy compounds and furthermore exert the ability to increase their coordination number to values above the appropriate oxidation state, hydrolysis and condensation rates are generally much faster for transition-metal alkoxides than those for corresponding silicon alkoxides .…”

Section: Introductionmentioning

confidence: 99%

Vanadia−Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties

et al. 1996

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Vanadia−silica mixed oxides were prepared via the sol−gel method involving acid catalysis together with prehydrolysis in order to achieve matching of the reactivities of vanadium(V) oxide triisopropoxide and tetraethoxysilicon(IV) precursors. Gelation was forced by the addition of basic solution. The as-received gels were supercritically dried by semicontinuous extraction with supercritical CO2 at 313 K (low-temperature aerogels). The effects of composition, aging, and calcination temperature on the chemical, structural, and textural properties of the solids were investigated. The oxides were characterized by N2 physisorption, XRD, vibrational spectroscopy, thermal analysis, UV−vis, and 51V NMR. The low-temperature vanadia−silica aerogels were mesoporous and highly disperse. The increasing V content from 5 to 20 wt % nominal V2O5 caused a gradual decline in V dispersion. For 30 wt % “V2O5” the continuous formation of V−O−V connectivity resulted in crystallization of V2O5. The effect of aging in basic medium confined to the textural properties, significantly increasing BET surface area and especially pore volume. The prepared aerogels revealed a marked lack of stability against both apolar solvents in the presence of peroxides and polar solvents. The marked thermal stability in air at ≤873 K, however, combined with mesoporosity and high V dispersion, render these solids promising catalysts for gas-phase reactions.

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Section: Introductionmentioning

confidence: 99%

Vanadia−Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties

et al. 1996

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“…Specifically, since alcohols have higher supercritical temperatures than carbon dioxide, there have been many recent reports on the effect of drying agent on the textural properties and crystallization behavior of aerogels (31)(32)(33). These results demonstrate nicely the accelerated aging that a gel undergoes at high temperatures and pressures.…”

Section: Preparation and Manufacturingmentioning

confidence: 91%

Aerogels

2000

Kirk-Othmer Encyclopedia of Chemical Technology

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Aerogels are low‐density and high‐porosity materials that are most commonly prepared by removing the pore liquid from a wet gel with supercritical extraction. The most extensively studied and characterized are silica aerogels, which can be prepared in the density range of 3 to 500 kg/m 3 through a proper control of preparative variables. The unusual properties of these materials, such as high surface area and pore volume, low thermal conductivity, and low dielectric constant, make them attractive for applications in diverse areas including thermal insulation, detection of high energy particles, and catalysis. The challenge is to produce them in a cost‐competitive process, which means exploring options that do not involve supercritical drying. Recent results show that with surface modification, aerogel‐like materials can indeed be produced at ambient conditions. Other ongoing research has been directed at the preparation and characterization of nonsilicate aerogels, as well as organic and inorganic–organic hybrid materials in an attempt to define their properties and to identify potential applications.

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“…Lower aliphatic alcohols (MeOH, EtOH, and i-PrOH) and CO 2 are usually employed as supercritical fluids (SCF) for the synthesis of aerogels, including binary ones [3]. The character of effect of SCF type on the physicochemical properties of SiO 2 -TiO 2 binary aerogels remains unexplored, however, it is known that drying with the use of alcohols results in formation of nanocrystalline titanium dioxide (usually as anatase) in SiO 2 matrix, whereas materials obtained using CO 2 or by drying under atmospheric pressure are homogeneous and X-ray amorphous [21][22][23].…”

mentioning

confidence: 99%

SiO2–TiO2 binary aerogels: Synthesis in new supercritical fluids and study of thermal stability

Yorov

Sipyagina

Baranchikov

et al. 2016

Russ. J. Inorg. Chem.

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A comparative analysis of properties of SiO 2 -TiO 2 binary aerogels prepared by supercritical drying using different supercritical fluids (isopropanol, hexafluoroisopropanol, methyl tert-butyl ether, and CO 2 ) has been performed. The use of different supercritical fluids allows preparation of both homogeneous amorphous SiO 2 -TiO 2 binary aerogels (by supercritical drying in hexafluoroisopropanol and CO 2 ) and composite aerogels containing nanocrystalline anatase (by supercritical drying in isopropanol and methyl tert-butyl ether). The thermal treatment of the aerogels at temperatures up to 600°C does not lead to considerable change in the porous structure and phase composition of the aerogels.

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A Comparison of Tio₂-Sio₂ Aerogels and Xerogels

Cited by 6 publications

References 10 publications

Vanadia−Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties

Vanadia−Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties

Aerogels

SiO2–TiO2 binary aerogels: Synthesis in new supercritical fluids and study of thermal stability

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A Comparison of Tio2-Sio2 Aerogels and Xerogels

Cited by 6 publications

References 10 publications

Vanadia−Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties

Vanadia−Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties

Aerogels

SiO2–TiO2 binary aerogels: Synthesis in new supercritical fluids and study of thermal stability

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A Comparison of Tio₂-Sio₂ Aerogels and Xerogels