Vol 91, No 5 (2017)

The solubility in a ternary fullerenol-d (C₆₀(OH)_22–24)–SmCl₃–H₂O system at 25°C is studied via isothermal saturation in ampules. The solubility diagram is shown to be a simple eutonic one that consists of two branches corresponding to the crystallization of fullerenol-d (C₆₀(OH)_22–24 · 30H₂O) and samarium(III) chloride SmCl₃ · 6H₂O crystallohydrates and contains one nonvariant eutonic point corresponding to saturation with both crystallohydrates. The long branch of C₆₀(OH)_22–24 · 30H₂O crystallization shows the effect of fullerenol-d salting out of saturated solutions; in contrast, the short branch of SmCl₃ · 6H₂O crystallization shows the pronounced salting-in effect of samarium(III) chloride.

Expressions are derived for the Gibbs and free energies of a liquid–vapor system. The critical parameters of the liquid are determined, and the character of the relationship between them is found. The temperature dependence of the vaporization heat is found. The analytical expression of the empirical Tait rule is substantiated. General patterns of subcritical and critical equilibria were revealed. A geometric definition of a critical state is proposed, and the existence of two critical states is proven.

The oxidative dehydrogenation of propane on a supported vanadium catalyst was studied (the support was a complex oxide system consisting of a ceria–zirconia solid solution deposited on γ-Al₂O₃ (CeZrO/γ-Al₂O₃)). A comparative analysis of the properties of the support and the catalyst prepared on its basis was performed. The support and catalyst were characterized by the BET method, scanning electron microscopy, X-ray diffraction analysis, and Raman spectroscopy. The catalytic properties of the catalyst and support were studied in propane oxidation at 450 and 500°C with pulse feeding of the reagent. The effect of propane on the support was found to improve the oxidative properties of the latter. This behavior of the support is related to the preparation procedure, which leads to the formation on its surface of the crystalline phase of the ceria–zirconia solid solution and amorphous ZrO₂ and Al₂O₃ phases and/or their solid solution. Similar processes occur with the catalyst support during the oxidative dehydrogenation, giving rise to additional active centers (CeVO₄).

Flame propagation in a closed tube over mixtures of chloromethane and chlorine of different compositions following ignition by continuous UV radiation is studied. It is found that the rate of combustion in all mixtures except limiting ones grows along with the propagation of the flame front up to its maximum values at nearly 1/3 the tube length and then slows. In limiting mixtures, the speed’s behavior is completely different. It is greatest near the source of UV light and gradually slows with distance from the source. The high speed in the initial section is due to the effect of UV light. The temperature of combustion is lowest in limiting mixtures, and the rate of chlorine molecule photodissociation at this temperature is comparable to and even faster than that of their thermal dissociation. The light in these mixtures thus contributes substantially to the initiation of the chemical reaction. It is concluded that when limiting mixtures are ignited by UV pulses, the speed of flame propagation falls markedly as it proceeds without the influence of radiation, and the character of changes in the speed’s behavior becomes identical to those for other mixtures.

Thermodynamic characteristics of the formation of the Schiff base between isoniazid and pyridoxal 5'-phosphate in an aqueous solution at different pH values of a medium are determined by means of spectrophotometry and calorimetric titration. The process kinetics is studied spectrophotometrically, and the reaction rate constants for the formation of the imine at different acidities of a medium are determined. Biochemical aspects of the binding of pyridoxal 5'-phosphate into stable compounds are discussed.

Ga and In ZSM-5 zeolites are obtained via hydrothermal crystallization from alkali aluminosilicate gels. Their physicochemical and catalytic properties during conversion of propane into aromatic hydrocarbons are studied. These catalysts exhibit different activity and selectivity in propane aromatization process due to their specific physicochemical properties and the localization of promoter atoms in different sites of the zeolite structure. A zeolite containing 1.85 wt % of gallium oxide is the most effective catalyst for propane aromatization.

The cooperation of Zn and Co in the Zn-Co/HZSM-5 catalyst was investigated. NO was selectively reduced by CH4 to N₂ in the presence of excess O₂, and the catalytic activity depended on both the activation of CH4 and the adsorption properties of NO_x. It was found that the addition of Zn could effectually heighten the selectivity of methane to NO_x. The results of H₂-TPR, NH₃-TPD and XPS proved that addition of Zn into Co/HZSM-5 could inhibit the formation of bulk Co₃O₄ on the outer surface of the catalyst. Reducing the bulk Co₃O₄ would restrain the combustion of methane and improve the selectivity of methane to NO_x, which was very consistent with the experimental results. MS-TPD results showed that Zn contributed the form of NO₂ and strengthened its adsorption on the Co/HZSM-5 catalyst. So the reaction mechanism is proposed to occur via two successive elementary steps. First NO is oxidized to NO₂ on the dispersed CoOx sites or Co²⁺ active sites; then NO₂ is adsorbed on Zn²⁺ sites, and further reacts with methane on proton acid sites. The key step is the adsorption of NO₂. Zn directly participates in the reaction by adsorption of NO₂.

The crystallization polytherm of the ternary CO(NH₂)₂–KNO₃–H₂O system is plotted for the first time via visual polythermal analysis and calculating ternary eutonics characteristics from data on the boundary elements of two-component systems. The ternary eutonics modeling error does not exceed 3.5%. In addition to the crystallization fields of individual components, the field of the redox reaction that occurs in the system between potassium nitrate and carbamide is shown in the CO(NH₂)₂–KNO₃–H₂O diagram by a dashed outline.

Several models of relaxation for the dielectric spectra of aqueous urea solutions in the microwave region are compared. The spectra are shown to contain two main Debye components arising from the rotational motions of urea and water molecules. Two essentially different concentration regions in urea solutions are identified. The first is characterized by a small increase in the mobility of water molecules (τ₁ = 7.8 ps) and the existence of hydrated urea molecules (τ₂ = 19 ps). Due to the aggregation of urea molecules, the relaxation times for the latter process grow considerably in highly concentrated solutions. At the same time, faster molecular motions (τ₃ = 6 ps) are observed for water molecules.

The effect of concentration on the self-diffusion coefficients of acetylsalicylic acid and methyl salicylate in methanol-d4 is investigated in the temperature range of 278–318 K using NMR. It is found that the self-diffusion coefficients increase along with temperature and fall as concentration rises. Within the limit of an infinitely dilute solution, the effective radii of solute molecules, calculated using the Stokes–Einstein equation shrink as the temperature grows. It is shown that the observed reduction of effective radii is associated with an increase in the fraction of solute monomers as the temperature rises. The physicochemical parameters of heteroassociation of acetylsalicylic acid and methyl salicylate with methanol are determined.

Binary spinels of Со and Мn are obtained by means of hard-template synthesis. Their structural and chemical characteristics are determined via N₂-BET, XRD, and TEM. Their catalytic activity is studied using methanol oxidation as the model reaction.

The motion of a lithium ion over a channel formed by sheets of perfect and defect (with monovacancies) silicene with a graphene support at different values of the channel gap is studied by means of molecular dynamics. It is established that the lithium ion enters the channel and passes through it at gap widths of 0.75 and 0.8 nm; at the same time, the monovacancies in the silicene sheets have a decelerating effect on the lithium transport over the channel. The ion passes through the channel in 12.6 and 8.6 ps for ideal silicene and 27.7 and 31.8 ps for defect silicene, respectively. It is shown that graphene sheets have a stabilizing effect that prevents the gap value from changing appreciably.

Powders of metal–carbon nanocomposites consisting of nanosized bimetallic Fe–Co particles dispersed in a carbon matrix are obtained via the IR pyrolysis of a precursor based on polyvinyl alcohol and metal-containing compounds. The obtained samples are investigated by X-ray diffraction and transmission and scanning electron microscopy. The morphology and dispersity of FeCo nanoparticles are studied, depending on the intensity of IR annealing.

Fe₃O₄ magnetic nanoparticles (MNPs) were prepared by co-precipitation method. The nanoparticles were silica coated using TEOS, and then modified by the polymeric layers of polypropylene glycol (PPG) and polyethylene glycol (PEG). Finally, the core-shell samples were decorated with Ag, Au, and Cu nanoparticles. The products were characterized by vibrating sample magnetometry (VSM), TGA, SEM, XRD, and FTIR methods. The antibacterial activity of the prepared samples was evaluated in inactivation of E. coli and S. aureus microorganisms, representing the Gram-negative and Gram-positive species, respectively. The effect of solid dosage, bacteria concentration and type of polymeric modifier on the antibacterial activity was investigated. TEM images of the bacteria were recorded after the treatment time and according to the observed changes in the cell wall, the mechanism of antibacterial action was discussed. The prepared nanostructures showed high antibacterial activity against both Gram-negative and Gram-positive bacteria. This was due to the leaching of metal ions which subsequently led to the lysis of bacteria. A theoretical investigation was also done by studying the interaction of loaded metals with the nucleotide components of the microorganism DNA, and the obtained results were used to explain the experimental data. Finally, based on the observed inactivation curves, we explain the antibacterial behavior of the prepared nanostructures mathematically.

Zinc ferrite (ZnFe₂O₄) nanoparticles were successfully synthesized from Zn(NO₃)₂ · 6H₂O and Fe(NO₃)₃ · 9H₂O by microwave hydrothermal method at 150°C for 1 h. Cubic ZnFe₂O₄ with particle size below 7 nm was formed in the solution at pH ≥ 6. The crystallinity and particle size of ZnFe₂O₄ nanoparticles were increased after calcination. The effects of pH of the precursor solution and calcination on the particle size and crystallinity of the particles were studied. At room temperature the products show superparamagnetic and ferromagnetic properties, determined by their size. The formation mechanism of ZnFe₂O₄ was also discussed according to the experimental results.

Results from investigating the parameters of helium absoption by hollow glass-crystalline cenospheres obtained at the Reftinsky regional power station in the city of Asbest are presented. The permeability coefficients of helium penetrating through shells are determined, and the apparent activation energy is estimated (Е_act = 33 ± 5 kJ/mol). The possibility of selectively extracting helium from mixtures of it and nitrogen is shown.

The adsorption of egg lecithin and cholesterol from chloroform solutions onto silicalite-1 (hydrophobic silica with MFI zeolite structure) is investigated. Adsorption isotherms of the L-type for lecithin and the S-type for cholesterol are obtained in the 0.05–4.5 mg/mL range of equilibrium lipid concentrations. The maximum adsorption for lecithin is 30 mg/g; for cholesterol it is 70 mg/g. Chloroform treatment results in the desorption of no more than 10% of the lecithin and up to 50% of the cholesterol from the silicalite-1 surface. The lecithin molecules in the monolayer on the silicalite-1 are oriented such that their hydrophobic tails are oriented toward the surface and are partially inside the pores of the adsorbent.

Molecular dynamics simulations was carried to investigate the structure and dynamics of [BMIM][PF₆] ionic liquid (IL) confined inside a slit-like silicon nanopore with pore size of 5.5 nm. It is clearly shown that the mass and number densities of the confined ILs are oscillatory, high density layers are also formed in the vicinity of the silicon surface, which indicates the existence of solid-like high density IL layers. The orientational investigation shows that the imidazolium ring of [BMIM] cation lies preferentially flat on the surface of the silicon pore walls. Furthermore, the mean squared displacement (MSD) calculation indicates that the dynamics of confined ILs are significantly slower than those observed in bulk systems. Our results suggest that the interactions between the pore walls and the ILs can strongly affect the structural and dynamical properties of the confined ILs.