N. A. Sipyagina

Functionalization of aerogels by the use of pre-constructed monomers: the case of trifluoroacetylated (3-aminopropyl) triethoxysilane

A novel strategy for aerogels functionalization, based on the preliminary modification of monomers before gelation, is proposed. The strategy is illustrated by the synthesis of trifluoroacetylated (3-aminopropyl) triethoxysilane (APTES)-based aerogels. An aerogel sample prepared by cogelation of APTES with tetraethoxysilane (TEOS), followed by trifluoroacetylation of free aminogroups, had a BET-surface area of 100–180 m2 g−1, while the samples prepared by cogelation of a preliminary trifluoroacetylated monomer with TEOS had a 2–5 times larger specific surface area. Trifluoroacetylated aerogels properties showed strong dependence on the supercritical drying media.

Methyltrimethoxysilane-based elastic aerogels: Effects of the supercritical medium on structure-sensitive properties

Effects caused by the type of solvent used for supercritical drying on the properties of methyltrimethoxysilane-based aerogels were studied. All of the aerogel samples studied were found to be hydrophobic and to efficiently adsorb nonpolar organic compounds.

Methyl tert-butyl ether as a new solvent for the preparation of SiO2–TiO2 binary aerogels

SiO2–TiO2 binary aerogels have been synthesized for the first time using methyl tert-butyl ether as supercritical fluid. It has been shown that the aerogels prepared in methyl tert-butyl ether and isopropanol contain nanocrystalline anatase and that amorphous SiO2–TiO2 aerogels with a homogeneous distribution of their components can be obtained in CO2. A considerable contribution to the large specific surface area of the aerogels is made by micropores, especially when supercritical drying is carried out in CO2 and isopropanol.

Effect of synthetic conditions on the properties of methyltrimethoxysilane-based aerogels

The effect of synthetic conditions on the properties of methyltrimethoxysilane-based aerogels is reported. All of the aerogels are hydrophobic and can efficiently adsorb organic compounds.

New Aerogels Chemically Modified with Amino Complexes of Bivalent Copper

The reaction of copper(II) pivalate with aminopropyltrimethoxysilane in molar ratio Cu(II): RNH2 = 1: 4 leads to the corresponding complex 1. The combined gelation of complex 1 and Si(OCH3)4 produces lyogels whose structure incorporates Cu(II). The supercritical drying of the lyogels in CO2 results in aerogels with specific surface area up to 260 m2/g containing bivalent copper. Drying of lyogels under supercritical conditions in isopropanol and methanol leads to reduction of Cu(II) into metal state.

Propylene oxide as a new reagent for mixed SiO 2 -based aerogels preparation

A two-stage technique is developed to synthesize SiO2-based aerogels using propylene oxide as a reagent. By this technique, we were able to synthesize mixed SiO2–Cr2O3 and SiO2–Yb2O3 aerogels containing 0.4–1.3% at. of the dopant.Graphical Abstract

Comparative analysis of the physicochemical characteristics of SiO2 aerogels prepared by drying under subcritical and supercritical conditions

SiO2-based aerogels have been produced be removing a solvent (ethanol or hexafluoroisopropanol) from lyogels both above and below the critical temperature of the alcohols (in the range 210–260 and 160–220°C, respectively). The resultant materials have been characterized by low-temperature nitrogen adsorption measurements, X-ray diffraction, thermal analysis, scanning electron microscopy, X-ray microanalysis, and small-angle and ultrasmall-angle neutron scattering. The results demonstrate that removing the solvent 20–30°C below the critical temperature of the solvent yields silica that is characterized by higher specific porosity and has the same or a larger specific surface area in comparison with the aerogels produced by drying under supercritical conditions. The nature of the solvent used and the solvent removal temperature influence the size and aggregation behavior of primary clusters and the cluster aggregate size in the aerogels.

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

A comparative analysis of properties of SiO2–TiO2 binary aerogels prepared by supercritical drying using different supercritical fluids (isopropanol, hexafluoroisopropanol, methyl tert-butyl ether, and CO2) has been performed. The use of different supercritical fluids allows preparation of both homogeneous amorphous SiO2–TiO2 binary aerogels (by supercritical drying in hexafluoroisopropanol and CO2) 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.