Russian Journal of Physical Chemistry A最新文献

A complex of tetra-3-carboxyphthalocyanine with copper that is insoluble in water is obtained. Thermal effects from dissolving crystalline tetra-3-carboxymetalphthalocyanine in aqueous solutions of various KOH concentrations (from 0.002 to 0.02 mol/L) at 298.15 K are determined via direct calorimetry. Measurements are made in a calorimeter using an isothermal shell with automatic recording of the temperature and electrical calibration at T = (293.15–308.15) ± 0.01 K and P = 100.5 ± 0.7 kPa. Standard enthalpies of formation of the products of dissociation of the tetra-3-carboxyphthalocyanine complex with copper in aqueous solution are calculated. Thermal effects of stepwise dissociation are calculated using the HEAT computer program.

Nanometer polymer microspheres have unique physical and chemical properties that make them valuable functional materials for various applications, such as photonic crystal engineering, wastewater treatment, catalysis, environmental protection, sensor technology, drug delivery systems, and smart biomimetic materials. These versatile microspheres have great potential for further development. With the development of novel polymerization techniques, different types of nanometer polymer microspheres have been synthesized and more and more attention has been paid to their potential applications. In this study, nanometer polymer microspheres containing biphenyl formaldehyde were synthesized by Schiff base reaction. We used Tri(4-aminophenyl)amine and 4,4'-biphenyldicarboxaldehyde as reactants, a mixture of 1 : 4 DMF and ethanol as solvent, glacial acetic acid as catalyst, and reflux heating to obtain nanometer-polymer microspheres. We also evaluated the adsorption performance of these microspheres using methyl orange as a simulated pollutant. We conducted a single factor experiment to investigate the effects of different ratios, dosages, times, and temperatures on adsorption efficiency. We characterized the nanometer-polymer microspheres by XRD, IR, and SEM techniques to examine their size, morphology, and structure. Experimental results showed that the optimal ratio for nanometer-polymer microspheres was 1 : 2, with an optimal dose of 25 mg. The optimal adsorption conditions were a temperature of 30°C and a time of 60 min. Since the pH of the solution ranged from 3 to 8, the zeta potentials of microspheres had a negative value. Meanwhile, zeta potentials became more negative as pH increased. The adsorption equilibrium data fit well with the Freundlich model. The microspheres had a stable and uniform rigid structure and good regeneration performance, with regeneration efficiency higher than 80% after five adsorption-desorption cycles.

The effect of the diameter of a capillary porous-layer column with a silica gel sorbent on the loading properties was studied. Three columns with diameters of 0.25, 0.32, and 0.53 mm with a regularly porous silica gel sorbent were prepared. The loading capacity of the column with a regularly porous sorbent with a diameter of 0.32 mm was 7.3 times higher than for a commercial GS-GasPro column of the same diameter. The influence of the amount of the injected sample on the resolution of chromatographic peaks was shown using the separation of C₄ aliphatic hydrocarbons as an example.

Li₃V₂(PO₄)₃ (LVP) is a prospective cathode material meeting the uninterrupted requirements due to the high theoretical capacity and operating voltage. Nevertheless, the electrochemical capability of pristine LVP is severely restricted under a high operating voltage. Herein, carbon decorated LVP was prepared through the process of citric acid assisted gel and subsequent heat treating. The crystalline phase, morphology, microstructure, and composition of obtained materials were examined using different methods. Transmission electron microscopy result exhibits that the crystalline LVP surface is coated with an amorphous carbon layer of about 3–5 nm thickness, and the LVP particles are connected by carbon. The electrochemical capability of LVP cathode at a cut-off voltage of 4.8 V was determined. The results exhibit the discharge capacity of carbon decorated LVP at 1 C decreases slowly from the initial 132.0 to 104.1 mA h g^–1 after 200 cycles. Correspondingly, the carbon decorated LVP delivers 78.9% capacity retention, which is much larger than that of pristine LVP (46.6%), suggesting the enhanced stability. In addition, the rate and Coulombic efficiency of carbon decorated LVP are also obviously enhanced compared to the pristine LVP. The work verifies a simple modification method to ameliorate the inherent drawbacks and electrochemical properties of LVP at high voltage.

In this work, the electrical conductance approach is used to investigate the molecular interactions between nonessential amino acid (L-glutamic acid) and carbohydrates (L-arabinose/D-xylose) at various temperatures. Many characteristics, including limiting molar conductance (({{Lambda }}_{{text{m}}}^{0})), Walden product (({{Lambda }}_{{text{m}}}^{0}{{eta }_{0}})), activation energy (({{E}_{{text{A}}}})), and thermodynamic parameters, were obtained for the binary and ternary solutions of L-glutamic acid (Glu) from the electrical conductance ((hat {k})) measurement. The acquired thermodynamic quantities were interpreted in terms of the systems’ physicochemical interactions. The behavior of small biomolecules (amino acid) and saccharides in solute-solvent interactions is shown by the influence of numerous parameters, including concentration, temperature, and the position of axial and equatorial –OH groups of the saccharides, on these quantities. Hydrophilic-hydrophilic or ion-hydrophilic interactions predominate in the systems that are being studied is supported by the UV–Vis spectroscopy investigations’ absorption values.

An interpretation is proposed for the dependence of the melting temperatures of an entire subclass of alkali metal halides on the chemical composition, based on an analysis of changes in different contributions to the internal energy of salts in the molten and crystalline phases with variation in the sum of the radii of their cations and anions. The expression for calculating the energy of liquid salt melts includes the contribution from charge–dipole interactions between ions, which is considered in a work based on thermodynamic perturbation theory with a basis in the form of a model of charged hard spheres. The Born–Mayer formula is used for the energy of the crystalline phase in the electrostatic part, while Debye’s formula is employed to consider the contribution from vibrations. An explanation is given for the lower values of the reduced melting temperatures of lithium and sodium halides, relative to other salts. It is shown that deviations of the reduced melting temperatures of lithium and sodium halides depending on the sum of ionic radii can be explained by Coulomb and translational contributions to the energy in the molten state, along with Madelung and Born contributions in the crystalline phase.

Coefficients of activity of alkali metal fluorides at 298 K in aqueous solutions are calculated according to the generalized Debye–Hückel theory using experimental values of the static dielectric constant of solutions. It is shown that calculations without optimized model parameters reproduce the nonmonotonic concentration dependence of the coefficients of activity. The dependence of the coefficients of activity on the radius of a cation is explained by the weakening of ionic association as the radius grows.

A series of chromium oxide catalysts supported on SiO₂ with 5 wt % chromium were synthesized and studied. Silica gel was synthesized by a procedure using the cetyltrimethylammonium bromide template and hydrocarbons capable of solubilization in CTMABr micelles, namely, hexane, cyclohexane, and toluene as “extenders.” The resulting series of supports and catalysts were characterized by physicochemical methods: low-temperature adsorption of N₂, XRD, SEM–EDX, and UV–Vis diffuse reflectance spectroscopy. The highest catalytic activity in propane dehydrogenation in the presence of CO₂ was exhibited by the 5Cr/SiO₂–hexane sample, whose surface contains Cr(III) coexisting with Cr(VI). At 750°C propane conversion was 59.8%; propylene selectivity, 56.2%.

The temperature dependence of the heat capacity of betamethasone valerate in the range from 5.5 to 346 K was measured for the first time by precise vacuum adiabatic calorimetry. The thermodynamic functions of betamethasone valerate, namely, heat capacity, enthalpy H°(T) – H°(0), entropy S°(T) – S°(0), and Gibbs function G°(T) – H°(0) were determined for the temperature range from T → 0 to 350 K based on the experimental data. The thermal expansion coefficients were determined by low temperature powder X-ray diffractometry.

The composition of the gas phase was identified for the first time up to a temperature of 2200 K by the Knudsen effusion mass spectrometric method, and the partial pressures of the vapor species during the evaporation of hydroxyapatite were determined. Ca₁₀(PO₄)₆(OH)₂ was evaporated from a Knudsen effusion cell made of tungsten. In the temperature range 1200–1300 K, Ca₁₀(PO₄)₆(OH)₂ undergoes dehydration, forming Ca₃P₂O₈, which evaporates in the form of PO, atomic calcium, and oxygen when the temperature further increases to 1750–2200 K.