Vol 90, No 1 (2017)

Change in the dispersity, microstructure, and adsorption properties of mesoporous magnesium hydroxide powders synthesized by the precipitation method from solutions upon introduction of surfactants and under the action of microwave and ultrasonic irradiation was studied. Highly dispersed nanostructured Mg(OH)₂ powders were obtained with average sizes of primary and secondary particles of, respectively, 13–27 and 180–383 nm. The specific surface area, pore volume, and average pore diameter of the samples under study varied, depending on the preparation conditions, within the ranges 86–98 m² g^–1, 0.491–0.737 cm³ g^–1, and 24–32 nm, respectively. It was shown that highly dispersed mesoporous magnesium hydroxide powders can be directionally synthesized by the precipitation method, which opens up wide opportunities for their application as nanoreactors for synthesis of nanosize isolated particles and development of poly-path catalysts on their basis.

Formation mechanism of the MnO₂ phase in the reaction of heterogeneous synthesis between Mn²⁺ and MnO₄^-ions on a solid aluminosilicate surface in aqueous solutions was studied. It was shown that, for lowsilica forms, the Mn²⁺ ion is oxidized by the MnO₄^-ion uniformly across the grain depth to give the MnO₂ phase and manganese manganites. For high-silica materials, the MnO₂ phase is formed on the outer surface of grains, with the decomposition of the MnO₄^-ion and formation of the MnO₂ phase and molecular oxygen. It was found that, for the clinoptilolite rock used as a solid support, the yield of the MnO₂ phase and its distribution over the particle volume depend on the penetration capacity of the MnO₄^-ion into the porous structure of this rock, determined by its composition. It is shown that the amount of the MnO₂ phase grows with increasing concentration of the MnO₄^-ion and treatment duration, with the phase thickness being 15–20 and 350–1050 μm for, respectively, high- and low-silica samples.

Sol-gel method was used to synthesize nanosize powders in the LaPO₄–YPO₄–(H₂O) and LaPO₄–HoPO₄–(H₂O) systems. Dense ceramic samples with high microhardness (up to 25 GPa) were formed from these powders by sintering at temperatures of up to 1600°C. The isomorphic capacity of the monoclinic LaPO₄ matrix for the second component (yttrium or holmium) simulating radioactive nuclides of the actinide-rare-earth fraction was found to be high. The composites are stable in aqueous solutions, which is indicated by the low concentration of lanthanum and yttrium ions during leaching test (~10^–7 g L^–1). The results obtained in the study can be used to develop new high-efficiency ceramic matrices for solidification of the actinide-rare-earth fraction of liquid wastes formed in processing of the spent nuclear fuel.

Effect of main characteristics of the gas medium on the absorbing properties of alkaline chemical absorbents is demonstrated. The following gas flow parameters were examined as variables: carbon dioxide content of the gas flow within the range 0.2–5.0 vol %, gas humidity of 25–90 rel %, and pressure in the zone of the chemisorption process in the range from 2 to 6 MPa. As objects of study served mixed chemical absorbents based on calcium, sodium, and lithium hydroxides.

Study of the physical and electrical properties of the Sr₂Fe_1.5Mo_0.5 + Ce_0.8Sm_0.2O_1.9 composite material and its electrochemical properties as an electrode in contact with lanthanum gallate based electrolyte based on in reducing media revealed an increase in the dilatometric curve slope at around 400°C. This corresponds to an increase in the thermal expansion coefficient from 12.8 × 10^–6 to 19.3 × 10^–6 °C^–1. An analysis of electrochemical impedance spectra by the relaxation-time-distribution method demonstrated the electrode reaction is localized in the frequency range 500–0.01 Hz. The electrical conductivity of the material under study was found to be about 17 S cm^–1 at 800°C in the atmosphere of humid hydrogen. The polarization resistance under the same conditions was about 0.15 Ω cm². The dependence of the polarization resistance on the partial pressure of hydrogen is linear with a reaction order of about–0.4, whereas that on the partial pressure of water has the opposite slope with a reaction order of about 0.2.

Photocatalytic activity of gypsum cements that are based on the building plaster blend and synthetic calcium sulfate and contain 2–10 wt % titanium dioxide of anatase modification was studied. The decomposition rate of the model contaminant (Rhodamine C) on the surface of a plaster blend containing 2 wt %TiO₂ becomes seven times higher under exposure to a full spectrum of a UV lamp, and 29 times higher under UV-A irradiation at λ > 320 nm. It was found that there are two competing processes (photocatalysis and direct photolysis), which affect the decomposition rate of Rhodamine C on the surface of the cements, depending on the UV irradiation spectrum.

Physicochemical relationships of the phase distribution of the reactants in epoxidation of fatty acid methyl esters of vegetable oils with performic acid generated in situ were determined.. The progress of epoxidation is accompanied by redistribution of the organic and aqueous phase volumes. The major cause of changes in the phase volumes is the transfer of peroxide oxygen from the aqueous phase into the organic phase upon formation of epoxy groups. A comparable change in the phase volumes is due to reactive extraction of aqueous phase components with the epoxy compounds formed.

The kinetic parameters of copolymerization of 1,3-butadiene and styrene in hexane under the action of a ternary initiating system consisting of n-butyllithium, amine-containing alkali and alkaline earth metal alcoholates, and 2,2'-ditetrahydrofurylpropane were studied. The molecular mass characteristics and microstructure of the synthesized copolymer samples were examined. Physicomechanical tests of specimens of butadiene–styrene rubber prepared from solution and of vulcanized specimens based on them were performed.

A procedure for coordination radical polymerization of methyl methacrylate in the bulk, initiated by the azobis(isobutyronitrile)–tri-n-butylborane binary system at 60°С, was developed. Butyl radicals participating in the initiation step were detected by EPR. These radicals are generated by complexation of cyanoisopropyl radicals with trialkylborane. The radical at the boron atom transforms from the C-centered to N-centered structure with the subsequent S_R2 reaction and fast generation of n-butyl radicals. As found by NMR and confirmed by kinetic studies, the tri-n-butylborane–initiator–monomer system stimulates generation of propagating poly(methyl methacrylate) radicals.

Rigid-chain heat resistant polymers (with poly-2,2'-p-oxydiphenylene-5,5′-bisbenzimidazole as example) were impregnated for the first time with a silver-containing precursor in formic acid and in supercritical carbon dioxide. A procedure allowing the precursor reduction to silver nanoparticles both throughout the volume by thermal annealing of the films in the temperature interval 100–150°С and in the targeted mode using lasers operating at 405 and 532 nm was developed. It opens prospects for developing a process for production of heatresistant optical gratings and light guides. The reduces nanoparticles and their agglomerates have the size in the interval 50–200 nm and give a plasmon band in the range 450–460 nm.

The use of hyperbranched polyesterpolyols of different generations favors firmer fixation of carbon nanotubes and silver nanoparticles as components of composite materials on the electrode surface (0.028 mg cm^–2), which improves the operation characteristics of monoamine oxidase biosensors. The size of silver nanoparticles (18–52 nm) depends on the conditions for preparing hyperbranched polyesterpolyols, and their use as electrode modifiers influences the analytical possibilities of amperometric biosensors. Silver nanoparticles (18 nm, data of atomic force microscopy) in polyesterpolyols of third generation (pH 10.0) as components of the developed biosensors extend the interval of determinable concentrations to 1 × 10^–4–1 × 10^–8 M and decrease the lower limit of determination to 3 × 10^–9 M, compared to the unmodified sensors, owing to enhancement of the analytical signal. The developed biosensors were tested in monitoring of drugs (antidepressants) in Coaxil and Auroriks drug forms with the relative standard deviation on the level of 0.052.

The kinetics of leaching of Karelian shungites (types I–III) with water at pH in the interval 1–12 was studied. Changes in the chemical composition and structure of the shungite substance were revealed by X-ray fluorescence analysis and scanning electron microscopy. The catalytic properties of shungite were studied in relation to the presence of oxygen in water. The optimum design of a shungite–carbonate installation for potable water treatment was substantiated.

Novel thiouracil thermal stabilizers for rigid poly(vinyl chloride) (PVC), 6-methyl-2-thiouraci (6M2TU), 5-methyl-2-thiouraci (5M2TU), and 6-propyl-2-thiouraci (6P2TU) were synthesized successfully via a precipitation method, and characterized with 1H NMR spectra. Investigation of these thiouracil derivatives as thermal stabilizers for poly(vinyl chloride) (PVC) was measured by thermogravimetric analysis (TGA), congo red test, fourier transform infrared (FTIR), and discoloration test. The results show that the thiouracil derivatives have strong ability to replace the labile chlorine atoms in PVC chains, but weak ability to absorb hydrogen chloride. Moreover, PVC stabilized with these thiouracil derivatives and calcium stearate (CaSt₂) exhibit greater stabilizing efficiency compared with traditional Ca/Zn stabilizers with the same concentration.

The 3D hierarchical CeO₂ microspheres assembled by many loosened nanocubes with a porous structure and an edge length of 300–600 nm have been successfully synthesized via controlling the morphology of CeCO₃OH precursors by a simple template-free hydrothermal route. It was found that the CeO₂ microspheres have a cubic fluorite structure and there are Ce³⁺ ions and oxygen vacancies in the surface of the samples. The photoluminescence measurement indicated that the CeO₂ samples exhibit excellent optical properties at room temperature and the emission intensity increases with the increase of concentration of oxygen vacancies. There is a red-shifting in the band gap of the material compared to bulk one, which is mainly attributed to the influences of Ce³⁺ ions, oxygen vacancies and the morphology of samples.