Russian Journal of Physical Chemistry A最新文献

The acid-base properties of thiopyrine (TP) were studied in the water–dimethylformamide and water–dimethylsulfoxide solvents containing 25, 50, and 75 vol % DMF and DMSO at 298 K and ionic strength of 0.1 mol/L (NaClO₄). The pK values of thiopyrine were determined over a wide range of pH values. Areas with different forms of thiopyrine were identified depending on the dimethylformamide and dimethylsulfoxide contents. It was established that pK of thiopyrine increases with the content of the organic solvent. Based on the obtained pK values it was found that in aqueous dimethylformamide and dimethylsulfoxide solutions, thiopyrine exhibits the properties of a weak base.

New sorbents based on Silipor 200 have been synthesized. The adsorption properties of their surface in relation to the following classes of organic compounds were studied: aliphatic alcohols, aldehydes, ketones, and esters. Chelate-type complex compounds were used as modifying additives to obtain noncovalently modified adsorbents: cobalt acetyl acetonate, benzoyl acetonate, ethyl acetoacetate, and diethyl malonate. The retention of organic substances was studied by gas chromatography, and the thermodynamic parameters of adsorption and Henry constants were calculated. The influence of the functional groups of the chelate on the adsorption heats, the adsorption entropy change, and the contributions of cobalt chelates on the SiO₂ surface to the retention of adsorbates were determined.

The heat capacity of sodium-cesium trimolybdate NaCsMo₃O₁₀ was measured by the adiabatic method in the range of 5–319 K. No thermal anomalies in the behavior of heat capacity have been found. However, a feature was revealed indicating the presence of a low-frequency peak in the density of phonon states. The Debye temperature at absolute zero was determined by extrapolating the experimental data to absolute zero. Based on the smoothed heat capacity values, the isobaric thermodynamic functions (entropy, enthalpy increment, reduced Gibbs energy) were calculated in the range of 0–320 K.

The physical properties of tritium were determined; its extraction from nuclear plants is required to prevent its penetration into the cooling system and reduce the release of isotopes into the environment. The structural, kinetic, and adsorption properties of compressed tritium containing the tungsten nanoparticle were calculated by ab initio molecular dynamics modeling in the temperature range of 293 ≤ T ≤ 2873 K. The first peak of the partial radial distribution function of W–³H decreases, and the self-diffusion coefficient of tritium continuously increases with temperature. A large number of peaks are present in the spectral density of atomic vibrations of the whole system over the entire temperature range under study. It was concluded that tritium has a high tendency to be adsorbed on the tungsten nanoparticle, and the temperature of the system is the main criterion of the level of this adsorption.

Density functional calculations applied to structural, electronic, and dynamic properties of ferric oxide and its modified Si doping system were explored in detail using the generalized gradient approximation imported in Cambridge Serial Total Energy Package (CASTEP) module. Crystal structures of the studied systems were optimized, and the polymorph prediction of the most organized cluster, identified with a specific space group, was estimated. Significant polymorph clusters were validated using calculated parameters such as energy, density, acceptance rate in the space group, and temperature. Molecular dynamics simulation was performed to support the stability conditions on the material surface. TD-DFT approach was conducted to understand the several electronic transitions inside the designed ferrite and silico-ferrite systems that demonstrated exceptional sensitivity to visible light. Molecular dynamic CO₂-adsorption models were studied to visualize the behavior of the adsorbed CO₂ molecules on the surface of Fe₂O₃ and Si@Fe₂O₃ with planes (0 0 1), in connection with the corrected parameter of basis set superposition error (BSSE). The adsorption annealing study exhibited the best non-covalent interactions between the adsorbed molecules and the surface of the designed systems.

A model and a solution method for a plug-flow reactor with pseudo-first-order reactions are proposed. These methods make it possible to identify a dependence of the process duration and the reactor steady-state attainment time on chemical process parameters, such as reactor volume and volumetric feed flow rate. As shown by the calculated data, at least one residence time or inverse volumetric feed flow rate is required for the process to attain steady state. It is also demonstrated that, in a continuous-flow reactor, reactant concentrations always attain steady state sooner than product concentrations; also, the product transition time is independent of the reaction kinetics and is determined by the average mixture contact time within the reactor.

The equilibrium distribution of components between the Dowex 50 sulfocationite and an aqueous solution containing picolinic acid and zinc nitrate was studied. The total concentration of the zinc cation and its complex with picolinic acid in the polymer reached 1.1 M. The possibility of preliminarily calculating the counterionic composition of sulfocationite based on the equilibrium constants of binary ion exchanges and the known composition of solution is shown.

The effects of electrolyte concentration (regulated by varying the amount of ethylene glycol), temperature, and graphene size (adjusted by expanding the original graphene unit cell to different extents) on the diffusion and structure of aqueous electrolytes in graphene supercapacitors were investigated using molecular dynamics simulations. By analyzing the average number of hydrogen bonds, number density distributions, mean square displacement, and diffusion coefficients, we found that temperature and concentration significantly influence the properties of the system, while graphene size has a minimal effect. As the concentration of ethylene glycol increases, the hydrogen bonding network among water molecules is gradually disrupted, leading to a decrease in the average number of hydrogen bonds between water molecules, while the average number of hydrogen bonds between water and ethylene glycol molecules increases. Ethylene glycol demonstrates a greater propensity for hydrogen bond formation compared to water molecules. Consequently, the addition of ethylene glycol effectively protects water molecules toward decomposition via electrolysis.

The results of measurements of adsorption and structural characteristics of ASD-6 powder modified with vanadium pentoxide in different concentrations are presented; the specific surface area and porosity of the powders were calculated. With a 5% vanadium pentoxide addition, the specific surface area of ASD-6 + 5%V₂O₅ increased more than fivefold, and the porosity amounted to 0.036895 cm³/g at an average pore width of 8.2686 nm, whereas pure ASD-6 has a specific surface area of 1.1388 m²/g. Taking into account the data on the specific surface area, porosity, and the results of physicochemical analysis, optimal concentrations of vanadium hydrogel have been proposed, which make it possible to obtain dispersed systems with the required properties.

The physicochemical and transport properties of polymer films based on polyetherimides Ultem-1000 and Siltem-1700 are presented. Using the gravimetric method, the sorption, diffusion, and permeability coefficients for a number of model gases (N₂, CH₄, O₂, CO₂) were determined, and ideal selectivities for key gas pairs (O₂/N₂, CO₂/CH₄) were calculated. It was found that membranes based on Siltem demonstrate significantly higher permeability for all gases studied, but are inferior to Ultem in selectivity. The transport of water (H₂O) and ammonia (NH₃) vapors through continuous polymer films was also investigated. The water vapor permeability coefficient was 2570 Barrer for Siltem and 1720 Barrer for Ultem; for NH₃ these values were 29 and 10 Barrer, respectively. The influence of the composition of the casting solution on the transport characteristics of Ultem membranes was studied: the highest permeability values were achieved using N‑methylpyrrolidone (NMP) as a solvent. The obtained data can be used in the design of membrane systems for the separation of hydrogen-containing gas mixtures, including ammonia recovery and hydrogen purification processes within the framework of low-carbon energy.