Doklady Physical Chemistry最新文献

In the field of hydrogen energy production, submicron powders and nanopowders of aluminum are of particular interest, since they are highly reactive towards aqueous solutions at ambient temperature and pressure in the absence or in the presence of minor amounts of activating agents to generate free hydrogen atoms. Electrostatic spraying can be used to distribute fine powders of aluminum. Currently, applications of electrostatic fields are quite diverse. As a result of electrostatic spraying, agglomerates are broken, and the surface wettability increases. Therefore, to solve the practically important problem of designing a hydrogen generator based on the controlled reaction of aluminum powder with water, preliminary studies of aluminum powder particles are required. In addition, charging of the aluminum particles can affect the oxidation profile and reactivity of the powder. All this indicates the relevance of research on the use of electrostatic field in hydrogen power engineering for new engineering solutions for hydrogen production. The results of the study were used to propose new applications of electrostatic field particularly in the industrial production of hydrogen energy. Highly dispersed aluminum powders were used as the object of research. The work is aimed at finding the optimal parameters for hydrogen generation in the reaction of finely dispersed aluminum powders with aqueous solutions. Experimental studies of pressure and temperature variation during electrostatic deposition of finely dispersed aluminum powders on the surface of a high-temperature reactor are presented.

The spectra of the polytetrafluoroethylene crystal lattice at temperatures close to the solid-state phase transition (PT) in this partially crystalline polymer were measured and analyzed. The increased sensitivity of the spectral parameters of the bands of external translational and rotational modes in these spectra to crystal effects made it possible to assign the PT at 292 K (19°C) not only to structural reorganization, but also to subsequent orientational disordering of the crystal lattice at 304 K.

The proposed study aimed to explore the kinetics of L-leucine (Leu) oxidation in a micellar media of cetyltrimethylammonium bromide (CTAB) by hexacyanoferrate(III) {HCF(III)}. The reduction in absorbance at 420 nm, which is indicative of the concentration of HCF(III), was measured to determine the reaction rate. Applying the pseudo-first-order state, The reaction’s progression was analyzed as an indicator of [HCF(III)], temperature, [Leu], [Cu(II)], [CTAB], ionic strength, and [OH^–]. The findings indicate that the [CTAB] is the crucial factor that significantly affects the rate of the reaction. The HCF(III) undergoes a 2 : 1 stoichiometric interaction with Leu and has a first-order reliance on [HCF(III)]. The observed reaction exhibits fractional-first-order kinetics with regards to [Leu], [OH^–], and Cu(II), within the range of concentrations investigated. The observed linear augmentation in reaction rate upon electrolyte’s introduction is suggestive of a positive salt effect. The inclusion of CTAB substantially enhances the catalytic activity of the process. After reaching its maximum rate, the reaction exhibits a very steady behavior even when the [CTAB] is further increased. The observed decrease in CTAB CMC could potentially be attributed to the diminished electrostatic repulsion among the cationic surfactant head groups, which is caused by the anionic [Cu(OH)₄]^2–, OH^–, and HCF(III) species.

The six-component high-entropy carbide (HEC) (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C has been studied. The electronic structure was calculated using the ab initio VASP package for a 512-atom supercell constructed with the use of special quasi-random structures. The artificial neural network potential (ANN potential) was obtained by deep machine learning. The quality of the ANN potential was estimated by standard deviations of energies, forces, and virials. The generated ANN potential was used in the LAMMPS classical molecular dynamics software to analyze both the defect-free model of the alloy comprising 4096 atoms and, for the first time, the model of the polycrystalline HEC composed of 4603 atoms. Simulation of uniaxial cell tension was carried out, and elastic coefficients, bulk modulus, elastic modulus, and Poisson’s ratio were determined. The obtained values are in good agreement with experimental and calculated data, which indicates a good predictive ability of the generated ANN potential.

Gold nanoparticles were prepared by metal vapor synthesis using isopropyl alcohol, acetone, and toluene as dispersion media. The electronic states of the metal and the nature of the adsorbed layer on the nanoparticle surface were investigated. Analysis of the photoelectron spectra of the obtained nanoparticles showed that regardless of the synthesis conditions, gold occurs in the Au⁰, Au⁺, and Au³⁺ states in all samples, and a carbon-containing shell is present on all types of metal particles. A study of the anticancer activity of nanoparticles in vitro using human cell lines revealed a dependence of the biological activity on the exposure time for samples obtained in a toluene dispersion medium. The metabolic activity of cancer cells treated with gold nanoparticles formed in isopropyl alcohol or acetone dropped in the very beginning of testing.

Anodic zirconia nanotubes are a promising functional medium for the formation of non-volatile resistive memory cells. The current–voltage characteristics in the region of low conductance of the fabricated Zr/ZrO₂/Au memristive structures were studied in this work. For the first time, an analysis was made of the reversible mechanisms of formation and destruction of single quantum conductors based on oxygen vacancies, which participate in processes of multiple resistive switching between low- and high-resistance states in the nanotubular dioxide layer. An equivalent electrical circuit of a parallel resistor connection was proposed and discussed to describe the observed memristive behavior of the studied layered structures.

Materials based on graphite-like carbon nitride g‑C₃N₄ were synthesized by heat treatment of a mixture of melamine and urea, and the effect of synthesis conditions on the photocatalytic activity of the samples was studied at various melamine : urea ratios. Platinum (1 wt %) was deposited on the surface of the synthesized g‑C₃N₄ samples as a cocatalyst. The produced photocatalysts were characterized by X-ray powder diffraction analysis, diffuse reflectance UV-Vis spectroscopy, and low-temperature nitrogen adsorption. Photocatalytic activity was determined in the reaction of hydrogen evolution from an aqueous solution of triethanolamine (10 vol %) upon irradiation with visible light (λ = 425 nm). Optimal conditions for the synthesis of the photocatalyst 1% Pt/g-C₃N₄ were found, which was obtained by calcination of a mixture of melamine and urea (1 : 3) and ensured an H₂ evolution rate of 5.0 mmol g^–1 h^–1 at an apparent quantum efficiency of 2.5%. The developed synthetic approach produces highly active catalysts because, during the synthesis, an intermediate supramolecular complex melamine–cyanuric acid is formed, which, upon further heating, is converted into g-C₃N₄ characterized by a high specific surface area exceeding 100 m² g^–1.

The synthesis verification of 3-amino-4-azido-1,2,5-oxadiazole and its structural characterization by IR, NMR spectroscopy, X-ray diffraction, and elemental analysis have been carried out. Its thermal behavior (TG-DSC), standard enthalpy of formation, sensitivity to mechanical stimuli, and detonation parameters have been studied. Our study has revealed the broad prospects of 3-amino-4-azidofurazan application as a precursor to novel energetic materials.

Phase equilibria in the Li–Mn–Eu–O system were studied for the first time in the temperature range 700–1000°С, and a concentration diagram was constructed within the Li–Mn–Eu triangle at an oxygen partial pressure of 21 kPa. It was shown that the LiEuO₂–Li₂MnO₃ section can be represented as quasi-binary, unlike the sections LiEuO₂–LiMnO₂ and LiEuO₂–LiMn₂O₄. It was determined that the isomorphic substitution of Eu for Mn in spinel LiMn₂O₄ (Fd(bar {3})m) does not exceed 2 mol %, while Li₂MnO₃ (C2/m) loses its single-phase character.

As structural descriptors in chemistry, indices based of information entropy are widely used. The change in information entropy in a chemical reaction is calculated as the difference of the values for the ensemble of products and the ensemble of reactants. In this work, for a generalized scheme of a catalytic reaction, analytical expressions were derived that relate the information entropy change in it with the parameters of individual steps and the corresponding overall equation. It was found that the sum of the parameters of individual steps is proportional to the information entropy change in the formal noncatalytic reaction, and the coefficient of proportionality is the fraction of atoms contained in reacting (forming) molecules of the ensemble of reactants (or products).