G. P. Murav’eva

Allylic isomerization of allylbenzene on nanosized gold particles

Nanosized gold particles immobilized on γ-Al2O3 exhibited catalytic activity in the allylic isomerization reaction of allylbenzene. As the size of gold nanoparticles was decreased from 40 to 2 nm, their specific activity per surface gold atom nonmonotonically increased from 0.5 to 110 (mol products) (mol Ausurface)−1 h−1. The particles greater than 40 nm were practically inactive.

Structural changes in wood during ozonation

It is found that ozone treatment of aspen wood leads to changes in its structural characteristics, i.e., its specific surface area and the crystallinity index of cellulose. Using optical microscopy, it is shown that ozonation is accompanied by a decrease in the average size and visible surface of wood particles. The values for the specific area of the outer surface of samples are calculated. The specific surface area available to the enzyme molecules is determined from data on the adsorption of inert protein hemoglobin on wood. It is shown that this value is an order of magnitude higher than that of the outer surface and increases considerably for an ozonized sample. Based on the results from X-ray analysis, it is established that the structure of cellulose is disordered during ozone delignification, as is indicated by a reduction in the crystallinity index and crystallite sizes.

An approach to unification of the physicochemical properties of commercial detonation nanodiamonds

In recent years, detonation nanodiamond is regarded as a promising material for biomedical applications. However, a significant problem that stops of intensive development of this area is a absence of commercial NDs standardization. This article presents the results of the study of physicochemical properties of several industrial nanodiamonds available in the international market. The differences of physicochemical characteristics of nanodiamonds produced, selected and purified in various ways are shown. A method is developed for industrial processing of nanodiamonds, that represents high-temperature hydrogenation of diamond surface and allows to unify their properties. It is shown that after these processing nanodiamonds have the same surface chemistry and can form stable hydrosols. The proposed method of industrial nanodiamonds unification can become a universal method of its standardization.

The kinetics and mechanism of doped corundum structure formation in an water fluid

The kinetics and mechanism of corundum formation from hydrargillite in an water medium under sub- and supercritical conditions in the presence of manganese ions was studied. The conclusion was drawn that corundum structure formation with the insertion and uniform distribution of manganese ions occurred thanks to solid-state mobility, which appeared under the conditions of reversible dehydroxylation in the interaction of a solid matrix with an water fluid. Complex defects containing Mn2+, Mn3+, and Mn4+ ions along with hydroxyl groups and oxygen vacancies were formed when corundum was doped with manganese ions in different charge states because of redox processes in a supercritical water fluid. Corundum doped with manganese exhibited ferromagnetic properties at room temperature.

Synthesis and physicochemical properties of biomorphic zirconia fibers

Biomorphic zirconia fibers were prepared by successive carbonization and/or calcining of sawdust impregnated by a solution of zirconium oxynitrate. Pyrolysis was performed in nitrogen (500°C), and calcining, in air (600°C). The physicochemical characteristics of samples were studied by adsorption measurements, electron microscopy, and X-ray diffraction. The biomorphic fibers were composed of zirconia nanoparticles not larger than 12 nm. The samples had a uniform phase composition dominated by the tetragonal ZrO2 phase; their specific surface area was 13–38 m2/g depending on the salt content in sawdust. It was assumed that the stabilization of the tetragonal phase could be related to the incorporation of mineral components (calcium, magnesium, and potassium compounds) of sawdust into zirconia; carbonization had no substantial effect on the properties of the resulting oxide. The method developed could be used to obtain tetragonal zirconia (without expensive reagents and water consumption) and utilize wood industry wastes.

Oxide talum-containing catalysts of ozone decomposition and methane oxidation

The oxidation of manganese ions is shown to occur in ozone decomposition on manganese-containing catalyst, leading to the deactivation of a sample. The structure of the iron-containing catalyst does not change, ensuring its high stability during ozone decomposition in a dry gas flow at room temperature, conducted in the region of inner diffusion with an activation energy of 15.5 ± 0.7 kJ/mol. The presence of manganese cations in the intermediate stages of reduction is found to increase their activity in the reaction of deep methane oxidation.

Synthesis of corundum doped with cerium in supercritical water fluid

The properties of fine crystalline corundum doped with cerium (α-Al2O3: Ce3+) during synthesis in a supercritical fluid have been studied. The synthesis of corundum has been carried out by the thermal treatment of hydrargillite, Al(OH)3, at T = 415°C and {ie290-1} MPa in reaction media that contained from 0.001 to 0.25 wt % of cerium. Cerium ions are incorporated into the boehmite lattice during the transformation of hydrargillite into boehmite, which forms fine monocrystals of the doped corundum with a size from 20 to 50 μm. The size of the corundum crystals increases with increasing pressure and increasing concentration of cerium. The synthesized α-Al2O3: Ce3+ reveals a luminescent band in the UV region at 352 nm and a blue band at 421 nm. The intensity of the cerium ion luminescence in corundum increases with an increase in the water fluid pressure during synthesis. The follow-up annealing of α-Al2O3: Ce3+ at 1400°C in a vacuum leads to a decrease in the luminescence. It has been concluded that spectrally active complex structures that include cerium ions, oxygen vacancies, and hydroxyl groups are produced in the media of a supercritical water fluid upon the synthesis of boehmite and corundum. Exposure to high temperatures causes their transformation.

Regularities of formation and luminescence of zinc sulfide nanoparticles modified with amino acids

The regularities of formation and luminescence of zinc sulfide nanoparticles modified with various amino acids were studied. The luminescence intensity of ZnS sols depends strongly on the nature of the modifier and from 30 to 40 times increases in the case of methionine and glycine or nearly completely disappears in the case of cysteine. Two main stages of formation of unmodified and surface-modified ZnS were revealed: a very rapid formation of ZnS nanoparticles and a relatively slow process of ordering of the internal particle structure with the formation of luminescence centers. In the case of modified objects, the role of such centers could be played by surface zinc ions bound to amino acids.

State of manganese ions in the structure of corundum synthesized in supercritical water fluid

The kinetics and formation mechanism of doped corundum (α-Al2O3) from hydrargillite (γ-Al(OH)3) in supercritical water fluid (SCWF) in the presence of manganese ions are studied. It was ascertained that due to the reversible dehydroxylation in an aqueous medium, solid-phase transformation of hydrargillite into boehmite (γ-AlOOH) and then into corundum occurs with the formation of well-faceted corundum micro-crystals that are uniformly doped with manganese. It was found that when Mn2+ or MnO4− ions are introduced into the reaction medium, Mn5+, Mn4+, Mn3+, and Mn2+ ions are observed in the synthesized corundum. Meanwhile, the manganese ions form a complex defect in the corundum structure, which comprises oxygen vacancies and hydroxyl groups. The defects in corundum that emerge upon doping with manganese in SCWF are different from those in corundum doped during high-temperature synthesis.

Preparation and study of colloid-chemical and optical properties of the nanocrystals of zinc sulfide modified with amino acids

The effect of some amino acids: cysteine, methionine, glycine, lysine, and aspartic acid, on the formation of nanoparticles of zinc sulfide in aqueous solutions at pH 5.5–10.0 was investigated. A method of obtaining stable sols of ZnS particles of 2–4 nm size with narrow distribution of the particle size was developed. The investigated nanoparticles are shown to be sphalerite, the cubic modification of zinc sulfide. The ZnS sols modified with methionine and glycine show intense luminescence at 415–425 nm.