A. N. Murashkevich

Physicochemical and photocatalytic properties of nanosized titanium dioxide deposited on silicon dioxide microspheres

The synthesis of SiO2 core-TiO2 shell composites from a titanium dioxide sol and a suspension of microspherical silicon dioxide is described. The main factors ensuring the formation of a composite with a preset morphology are the size and charge of the TiO2 sol particles (10–45 nm) and silicon dioxide core particles (300–700 nm), the pH values of the suspensions of the starting components and the resulting composite, and the proportions and way of mixing of the siliconand titanium-containing components. The SiO2 core-TiO2 shell composites show high photocatalytic activity in the degradation of Rhodamine FL-BM dye (rate constant of k = 0.0813 min−1) and are much more active than precipitated TiO2 powder (k = 0.0022 min−1). The activity of the composite is determined by the calcination temperature (700–800°C), by the proportion and accessibility of the active component (TiO2), and by the presence of a dopant (P2O5).

Asymmetric Biginelli Reaction Catalyzed by Silicon, Titanium and Aluminum Oxides

The asymmetric Biginelli reaction was investigated in the presence of N-[(2S,4R)-4-hydroxyprolyl]-(S)-1-phenylethylamine as chiral inducer and silicon, titanium or aluminum oxides (individual and mixed, bulk and nanosized) as heterogeneous catalysts. It has been shown that all studied oxides improve chemo- and stereoselectivity of the Biginelli reaction.Graphical Abstract

The effect of the synthesis conditions of aluminum-modified nanosized titanium dioxide on the efficiency of its use in electrorheological dispersions

A comparative study of the physicochemical properties of nanodispersed TiO2 samples synthesized from TiCl4 by the sol–gel and coprecipitation methods has shown the advantages of the former from the points of view of both the specific surface area and electrorheological response of the obtained filler in 5% electrorheological dispersions. A correlation has been revealed between the temperature of TiO2 treatment (600–800°C) and its structure, phase state and electrorheological response. The maximum shear stress increment has been observed for dispersions of TiO2 samples that contain 7–10 mol % Al and have been thermotreated at 700°C for 3.0–3.5 h.

Synthesis of oxocyclohexenecarboxylic acids and podands derived therefrom under heterogeneous catalysis

Nanosized Al, Mg, and Ti-Si oxides, as well as barium hydroxide, have been tested as heterogeneous catalysts in the Robinson reaction with 2-ethoxy-substituted chalcone and podands based thereon. Barium hydroxide catalyzes the first step of the Robinson reaction, Michael addition, while its activity in the second step involving intramolecular cyclization and dehydration is lower. Nanosized oxides effectively catalyze the second step of the Robinson reaction and hamper elimination of the carboxy group. Procedures have been developed for the synthesis of oxocyclohexenecarboxylic acid derivatives and symmetric and asymmetric podands based thereon.

Physicochemical and electrorheological properties of titanium dioxide modified with metal oxides

The properties of electrorheological fluids containing dispersed phase of titanium dioxide nanoparticles prepared via the sol-gel method and modified with metal oxides have been studied. Titanium dioxide has the anatase structure with crystallite sizes of 8–10 nm and a specific surface area of 90–140 m2/g. It has been found that the magnitude of the electrorheological response of the filler is determined by the specific surface area and the content of a modifying component. The strongest electrorheological response has been revealed for titanium dioxide modified with aluminum oxide at an Al content of 6.5–7.0 mol % relative to TiO2.

Preparation, microstructure and electrorheological activity of nanosized modified titanium dioxide and titaniferous fillers

Nanodisperse powders of pure, superficially and structurally modified titanium dioxide as well as composition materials SiO2–TiO2 with different morphology are synthesized. Electrorheological properties of dispersions on their basis are investigated. It is established, that doping of TiO2 by heterovalency replacement of the titanium with aluminum and chrome ions allows us to raise essentially electrorheological activity of dispersions in comparison with pure titanium dioxide.

IR-Spectroscopic Study of Adsorption of Aminoazoles on Oxide Catalysts of Biginelli Reaction

Adsorption of 5-aminotetrazole and 3-aminotriazole on the surface of nanosized oxides of Al and Si–Ti, which are catalysts of the Biginelli reaction with the participation of aminoazoles, have been studied using the method of IR spectroscopy. It has been shown that 5-aminotetrazole and 3-aminotriazole interact with the Brønsted base centers on the oxide surface, with the behavior of aminoazole in the Biginelli reaction being determined by the coordination.

New chiral proline-based catalysts for silicon and zirconium oxides-promoted asymmetric Biginelli reaction

4-Hydroxy-(2S)-prolines bearing 3,4-dihydro-2H-1,4-benzoxazine or 1,2,3,4-tetrahydroquinoline fragments were synthesized and studied as chiral catalysts in the Biginelli reaction. The target product ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate was obtained with 54% enantiomeric excess (ee). An increase in ee values of the reaction product up to 76% was observed in the presence of nanosized oxides SiO2–ZrO2 as heterogeneous promoters.

Time stability studies of electrorheological response of dispersions with different types of charge carriers

The behavior of hydrous and anhydrous fillers of various types in the electric field is investigated. Rheological and dielectric properties of dispersions containing 20 wt% of the filler in the insulating oil are determined. The comparative results of the experimental determination of the change in shear stress and current density over time at the impact of the electric field of different intensity are presented.