Russian Journal of Physical Chemistry A最新文献

Spectroscopic investigation supported by molecular modeling methods has been used to describe the inclusion complex of β-cyclodextrin (β-CD) with Benzoxazolinone in solution and in solid state. By using UV-Vis absorption, the stoichiometric ratio of the complex was found to be 1 : 1 and the stability constant was evaluated as 410 000 (mol/L)^–1. Solid state characterization by FT-IR spectroscopy provided remarkable evidences of the formation of inclusion system. Moreover, semi-empirical calculations using PM3 level of theory and hybrid method ONIOM2 clearly indicate that the formed complexes are energetically favored in vacuum and in solution. Semi-empirical calculations using PM3, ONIOM2 (B3LYP/6-31G(p,d): PM3) methods, in vacuum and in acetonitrile were performed. The negative energy values obtained demonstrate clearly that the benzoxazolinone molecule can form a stable inclusion complex with β‑CD and the B orientation is significantly more favorable than the A orientation. From NBO analysis, the mutual interactions between β-CD and BOA were analyzed and discussed.

Azobenzene has been particularly concerned as promising candidates for solar thermal fuel and photo-switch for controllable latent heat release of phase change materials recently, due to its unique photo-isomerization reversibly between trans- and cis-isomers. The thermal property of azobenzene is closely involved in these solar and thermal energy related applications, and consequently needs to be extensively investigated and fully understood. Herein, we have reported the heat capacity study of trans-azobenzene using a combination of Physical Property Measurement System (PPMS) relaxation calorimeter and adiabatic calorimeter in the temperature range from 1.9 to 380 K. The heat capacity data have been fitted to a series of theoretical and empirical models, and the corresponding thermodynamic functions have been calculated based on the thermodynamic relations and fitting parameters. The standard molar heat capacity, entropy, and enthalpy of trans-azobenzene at 298.15 K have been determined to be 229.5 ± 1.1 J K^–1 mol^–1, 239.1 ± 1.2 J K^–1 mol^–1, and (35.56 ± 0.18) kJ mol^–1, respectively. Moreover, the other thermal properties of trans-azobenzene, such as thermal stability, thermal conductivity, formation enthalpy, phase transition temperature and enthalpy have also been measured using various thermal analysis and calorimetry technologies. These thermodynamic and thermal properties reported in this work can provide important fundamental basis for further studying and understanding azobenzene upon its structure transformation and functional performance, and consequently promote its application in solar thermal fuel and phase change materials for thermal energy utilization.

The effect of synthesis temperature on catalytic activity of oxygen electroreduction reaction (ORR) catalysts based on multi-walled carbon nanotubes (MWCNT) doped with cobalt and copper phthalocyanines and modified with palladium was studied. Pyrolysis of phthalocyanines was carried out in an inert atmosphere at different temperatures—750, 850, and 1000°C. SEM study showed that the particle size increases with increasing temperature of synthesis. Raman spectroscopy showed that the catalyst synthesized at 1000°C is characterized by a hierarchical structure due to the formation of a structured graphite layer on the surface. XPS method showed that increasing of the synthesis temperature from 850 to 1000°C does not lead to the disappearance of nitrogen in the material, but inactive types of nitrogen are transformed to more active ones: pyridine and pyrrole. The XRD method showed that the MWCNT_CoPc_CuPc_Pd_1000 catalyst contains copper-palladium intermetallics (Cu₃Pd and Cu_2.85Pd_1.15) and metallic cobalt in its structure, which contributes to an increase in the efficiency of the oxygen electroreduction reaction in an alkaline electrolyte. In the electrokinetic region, the most effective catalyst is MWCNT_CoPc_CuPc_Pd_1000. The E_1/2 value for the MWCNT_CoPc_CuPc_Pd_1000 catalyst is slightly inferior to the commercial platinum catalyst with a metal content of 40 wt %; the difference in E_1/2 values is about 0.02 V. Corrosion tests lead to a slight increase in the efficiency of the MWCNT_CoPc_CuPc_Pd_1000 catalyst: the E_1/2 and E_onset values increase by 0.005 and 0.001 V, respectively. This effect may be associated with self-activation of the catalyst surface.

The thermal effects of dissolution of 1-aza-18-crown-6 in water–ethanol and water–dimethyl sulfoxide mixed solvents at 298.15 K were determined by calorimetry. In water and aqueous organic solvents with initial cosolvent additions, dissolution of 1-aza-18-crown-6 is exothermic. When the cosolvent content exceeds 0.2 mole fractions, the dissolution of 1-aza-18-crown-6 is accompanied by an endo effect, which increases with the contents of both ethanol and dimethyl sulfoxide. The enthalpies of transfer of 1-aza-18-crown-6 from water to aqueous ethanol and dimethyl sulfoxide solutions were calculated. The enthalpy characteristics of crown ether solvation in aqueous organic solvents were compared.

Thermodynamic modeling is used to study the effect additives of a number of organic substances have on the temperatures of incipient crystallization of kerosene fractions (KFes) derived from crude oil (straight-run KFes (SRKFs)) and produced in the catalytic hydrocracking of heavy oil residues (HCKFs). Normal paraffins ({{{text{C}}}_{n}}{{{text{H}}}_{{2n + 2}}}) (n = 9, 11, 16) are used as additives to KFes, and m-ethylbutylbenzene is employed as an aromatic hydrocarbon. It is shown the UNIFAC and UNIQUAC models allow the reproduction of published experimental data showing that adding normal paraffins to HCKFs greatly raises the freezing point when n ≥ 11. For SRKFs, this rise starts at n = 16. Calculations show that m-ethylbutylbenzene additives have hardly any effect on the temperature of incipient crystallization.

Results are summarized from liquid chromatography of a complex mixture of unsaturated lipid molecules as the basis of a hydrophobic matrix of biomembranes. Data on the relative retention of such lipids, including residues of the most important fatty acids, allow calculations of the most characteristic general parameters that satisfactorily determine their behavior when a silver salt is introduced into a planar or column liquid chromatographic system in order to sharply increase the selectivity of separating unsaturated lipid molecules. A variant is proposed of quantitatively assessing the relationship between the selectivity of separating individual molecules of natural lipids with the proposed parameters of fatty acid residues included in their composition, which are calculated on the basis of variations in the chemical potential of such molecules when silver appears in this system.

An internal resistance heating method was proposed to control the operating temperature of Li-ion batteries to address rapid performance degradation under low temperature conditions. Main research content: (a) Preparation and process optimization of PTC (positive temperature coefficient) effects materials: Using micrometer nickel powder as the conductive material and polypropylene/polyvinylidene fluoride (PP/PVDF) as the polymer matrix. The polymer matrix was mixed with the conductive material using high-temperature melting method. The PTC materials with a transition temperature below 40°C were prepared through controlling the preparation process repeatedly and meticulously, and the optimal preparation process was determined. (b) Performance testing and analysis of PTC materials: The thermal analysis, volume change analysis, structure and micro-structure analysis were conducted through resistivity temperature curve, tensile performance, SEM and thermal expansion testing, respectively. The influence of conductive material content, heat treatment temperature, heat treatment time on the performance of PTC materials was systematically studied. (c) “Self heating Battery” assembly and performance study: A self heating Li-ion battery was assembled and its electrochemical performance was tested systematically. The results showed that the low-temperature discharge performance of the battery was significantly improved. This work can help improve the low-temperature performance of Li-ion batteries and expand its application areas.

The heat capacity of magnesium–neodymium hexaaluminate NdMgAl₁₁O₁₉ with a magnetoplumbite structure was measured by relaxation, adiabatic, and differential scanning calorimetry in the temperature range 2–1850 K. The data were smoothed after matching the temperature dependences of heat capacity obtained by different methods. The thermodynamic functions (entropy and change of enthalpy) were calculated, and the anomalous Schottky heat capacity in the low temperature region was estimated.

The Ni/CNTs-SnO₂ composite electrodes were prepared by the composite electrodeposition method. The influence of the incorporation of CNTs-SnO₂ on the hydrogen evolution reaction (HER) of Ni coating was investigated. The Ni/CNTs-SnO₂ composite electrodes were demonstrated successfully by SEM, XRD and EDX. The physical characterization indicated that the average sizes of the CNTs-SnO₂ particles were about 120 nm. The incorporation of CNTs-SnO₂ had been altered the preferred orientation of Ni coatings and the microscopic morphology of composite coatings. The Ni/CNTs-SnO₂ composite electrodes were tested by LSV, Tafel, EIS and CP to define their catalytic activity and stability for the HER. Compared with the Ni coating, the Ni/CNTs-SnO₂ composite electrodes had a larger specific surface area, which could provide more catalytic active sites for the HER. The overpotential of the HER was reduced. The electrocatalytic hydrogen evolution performance of the composite electrodes were improved. At a cathodic current density of 10 mA/cm², the Ni/CNTs-SnO₂ composite electrodes prepared with 0.75 g/L of CNTs-SnO₂ displayed a lowest overpotential (259 mV) for HER, which demonstrated the highest catalytic activity for HER.

Quantum chemical calculations of binary complexes of methane, ethane, and propane with hydrogen chloride, having an intermolecular С⋅⋅⋅H−Cl bond, were performed by the MP2/aug-cc-pVTZ method. It was shown that the binding of an alkane with an HCl molecule is possible at different mutual orientations of the monomers; the properties of the resulting complexes are similar to those of molecular systems with a typical hydrogen bond. Elongation of the covalent H−Cl bond upon complexation is observed with a frequency shift of the corresponding IR band of the stretching vibrations to the long-wave region and a chemical shift on the bridging hydrogen atom characteristic of H-bonded complexes. The analysis of the nature of the intermolecular bond included decomposition of the binding energy into components, as well as NBO analysis and a study of electron density topology using the AIM method of Bader’s theory. The potential curves of intermolecular interaction and maps of electron density shift upon complexation from monomers were plotted.