Alena N. Malkova

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.

Hexafluoropropylene Oxide–Alcohol: A Convenient System for Silica Dissolution

Abstract A new method of silica dissolution is described. It involves the formation of a stable SiF4 · n ROH complex (1, 1a) just from SiO2 and anhydrous alcoholic HF generated in situ from commercially available hexafluoropropene oxide. Alcoholic SiF4 complexes can be easily converted to different organosilicon compounds of the type SiF4L2 and (LH)2SiF6 [L = 1,10-phenantroline (2a), 2,2′-dipyridyl (2b), Me2SO (2c), pyridine (2d), triethanolamine (3a)]. Different silica-containing compounds can be used in this strategy—silicagel, sand, alumosilicates, and even rice husk. GRAPHICAL ABSTRACT

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.

Perfluoropropylene oxide as a reagent for the synthesis of germanium, titanium, tin, and zirconium fluorides

A new method of preparation of germanium, titanium, tin, and zirconium fluoride alcohol complexes by reaction of the metal oxides with a solution of perfluoropropylene oxide in methanol is developed. The reaction of the complexes obtained with ligands (L = 1,10-phenanthroline or dimethyl sulfoxide) was studied, and the structure of the obtained compounds was determined. A new route to the synthesis of 1-fluorogermatrane is developed.

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.

1-hexene oligomerization by fluorinated tin dioxide

Fluorinated tin dioxide has been shown to exhibit catalytic activity for 1-hexene oligomerization. The physicochemical and functional properties of nanocrystalline fluorinated SnO2 have been studied.