Doklady Physical Chemistry最新文献

This study investigates the structural, optical, and thermal properties of chitosan (CS) biopolymer using experimental and computational approaches. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of two key functional groups–hydroxyl (OH) and amine (NH/NH₂)–which play a crucial role in CS interactions. X-ray Diffraction (XRD) analysis revealed a mixed-phase structure, comprising both crystalline and amorphous regions. Various crystallographic parameters, including full width at half maximum (FWHM), degree of crystallinity, lattice strain, dislocation density, inter-band crystallinity, and stacking faults, indicated an increase in crystallinity with greater CS film thickness. Optical characterization using Tauc plots showed a decrease in bandgap energy from 5.54 to 5.12 eV with increasing film thickness. Urbach energy analysis allowed for the estimation of steepness parameters and electron-phonon interaction energy (E_e–ph), which exhibited a reduction from 11.398 to 10.315 eV. Computational studies were performed using Density Functional Theory (DFT) at the B3LYP/6-311++G(d,p) level via the Gaussian 09 program to determine electronic and thermal properties. Additionally, thermal properties such as entropy, heat capacity, and enthalpy were evaluated using the Materials Studio software. Monte Carlo simulations were employed to estimate the adsorption energy of CS on Fe, Al, and Cu surfaces, revealing that Fe exhibited the most stable and strong coordination with CS due to its unique coordination geometry. These findings provide valuable insights into the structural and functional characteristics of CS films, contributing to their potential applications in various fields.

The crystal structures of three organic salts of triiodaminobenzoic acid (1–3) and triiodaminobenzoic acid monohydrate (4) are described, the structural features are established by the X-ray diffraction method. Compound 1: C₂₀H₁₉I₆N₃O₆, FW 1158.78; monoclinic crystal system, space group Сс; unit cell parameters: a = 32.0782(10) Å, b = 9.5284(3) Å, c = 9.3745(3) Å; α = 90°, β = 90.0(1)°, γ = 90°; V = 2865.35(16) ų, Z = 4, ρ_X = 2.684 g/cm³. Compound 2: C₁₆H₁₅I6N₃O₄, FW 1074.71; monoclinic system, space group P2₁/c; unit cell parameters: a = 8.990(5) Å, b = 28.541(11) Å, c = 9.945(5) Å; α = γ = 90°, β = 91.23(2)°; V = 2551(2) ų, Z = 4, ρ_X = 2.798 g/cm³. Compound 3: C₁₇H₁₇I₃N₂O₄, FW 694.03; monoclinic system, space group I2/a; cell parameters: a = 36.02(2) Å, b = 7.254(5) Å, c = 16.468(9) Å; α = γ = 90°, β = 105.29(2)°; V = 4150(4) ų, Z = 8, ρ_X = 2.222 g/cm³. Compound 4: C₇H₆I₃NO₃, FW 532.83; orthorhombic system, space group Iba2; unit cell parameters: a = 30.2146(4) Å, b = 13.9830(2) Å, c = 5.80740(10) Å; α = β = γ = 90°; V = 2453.57(6) ų, Z = 8, ρ_X = 2.885 g/cm³. The 7-methylquinoline salt is devoid of halogen bonds because of the peculiarities of the stacking of flat molecules. For two compounds (3 and 4), the features of their thermolysis are determined by thermal analysis (in an argon atmosphere): at the first stage (52 and 73°C, respectively), the loss of crystallization water occurs; at 700°C thermolysis of both compounds gives glassy carbon as the decomposition product.

Strontium molybdate was prepared by fluxed-melt chemical synthesis from ionic melts of the Me,Sr||Cl,МоO₄ (Ме = Li, Na, or K) three-component reciprocal salt pair systems fluxed with the low-melting-point eutectic melt of the LiCl–NaCl–SrCl₂ three-component system as the flux electrolyte. The eutectic chloride melts used as the fluxes provided a significant decrease in temperature and an increase in reaction rate of chemical strontium molybdate synthesis in ionic melts.

High-performance polymers characterized by their exceptional thermal stability are crucial across various industries. Here, phthalonitrile resins have attracted significant attention due to their ability to form highly cross-linked networks upon curing, leading to outstanding properties suitable for demanding applications in aerospace, electronics, and automotive sectors. This study investigated the thermal curing kinetics and resulting thermal stability of phthalonitrile resins cured with 4,4'-diaminodiphenyl sulfone (DDS) and bisphenol A diglycidyl ether (DGEBA). Kissinger and Friedman methods were employed to analyze the curing process using thermogravimetric analysis data at various heating rates. The results revealed that DGEBA-cured networks exhibited higher thermal stability and activation energy compared to DDS-cured networks. This was attributed to the stronger C–O bonds formed in DGEBA networks. The higher bond dissociation energy of C–O bonds, arising from factors including electronegativity difference, bond length, orbital overlap, and hybridization necessitates a greater energy input for bond cleavage during thermal degradation. These findings highlight the critical role of curing agent selection in tailoring the thermal properties of phthalonitrile-based materials for high-performance applications.

The effects of components of intumescent systems based on silane-terminated polyether (STP) polymers on their thermolysis character were studied. Thermal analysis and fire-resistance tests showed that neither the molecular weight of the STP polymer, nor a moderate change in the ratio of components in the intumescent system relative to the selected base composition, has a significant effect on the thermolysis, whereas a change in the amounts of fillers such as kaolin and, in particular, titania, provides doubling of the fireproof rating of the studied coatings due to the structuring of the char foam formed upon thermal destruction and acts as a heat-insulating coating. These results may be of significant importance in the development of heat-expanding fire-protection compositions based on STP polymers.

Nitrogen-doping of platinum/carbon (Pt/C) catalysts in proton exchange membrane fuel cells (PEMFCs) have garnered significant attention due to its potential to enhance catalyst performance by improving the dispersion and stability of Pt nanoparticles. However, the leaching of nitrogen dopants (N-dopants) under the harsh operational conditions of PEMFCs presents a formidable challenge, leading to catalyst degradation and reduced fuel cell efficiency. Understanding this issue is critical for advancing the development of durable and cost-effective PEMFC catalysts. This review critically examines the mechanisms of N-dopant leaching, encompassing electrochemical factors. By integrating insights from recent experimental and theoretical studies, this review recognizes the primary causes of N-dopant leaching and evaluates various mitigation strategies. Key findings include the identification of specific degradation pathways and the effectiveness of different stabilization techniques. The implications of these findings suggest new directions for catalyst design, aiming to improve the stability and longevity of N-doped Pt/C catalysts for PEMFC. This review concludes with recommendations for future research, emphasizing the need for continued exploration of innovative approaches to enhance the durability of N-doped Pt/C catalysts.

Homogeneous and heterogeneous homophase reactions in an oscillating mode are studied. Conditions for free concentration oscillations to arise in a closed homogeneous reaction system are determined. A quantitative description is given to the oscillating mode of a heterogeneous homophase reaction with special attention paid to the formation of Liesegang patterns.

Precise estimation of aggregate size of asphaltene particles in oil reservoirs characterized with the resulted formation damage and well blockage issues are critical to the smooth oil production and successful planning of pertinent remedial tasks. In this research, it is aimed to construct data-driven soft-computing based models of Extra Trees (ET), Multilayer Perceptron Artificial Neural Network (MLP-ANN), Support Vector Machine (SVM), Convolutional Neural Network (CNN), Random Forest (RF), K-nearest Neighbors (KNN), Adaptive Boosting (AdaBoost), Ensemble Learning (EL), Decision Tree (DT), Linear Regression, Ridge Regression, and Lasso Regression to predict asphaltene aggregation size in terms of time, asphaltene concentration of model oil, heteroatoms content of asphaltenes, hydrogen content of asphaltenes, and voltage based upon previously published experimental data. A widely recognized outlier identification methodology is implemented to the collected dataset to evaluate its reliability prior to model development. Furthermore, the relevancy index is calculated for every input variable to determine its relative impact on aggregation size. K-fold cross validation algorithm is used during model training to reduce overfitting. It is indicated that in contrast to asphaltene hydrogen content, other parameters such as voltage, time, asphaltene concentration and hydrogen content of asphaltenes are all directly influencing aggregate size. Moreover, both graphical and statistical evaluations demonstrate that the CNN model surpasses all other examined constructed models in performance as evidenced with lowest value in mean squared error and largest value of coefficient of determination.

This work is devoted to the search for methods of labeling powder materials. The labeling was performed with CdSe/CdS/ZnS quantum dots synthesized in an oleic acid medium. Cyanuric acid powder was selected as a bulk material model for the study. The choice of cyanuric acid as a model powder material was justified by its low toxicity, relative cheapness and accessibility, as well as insolubility in organic solvents used for the quantum dots synthesis. In addition, the criterion for choosing cyanuric acid was that its own luminescence spectrum was shifted relative to the spectra of the quantum dots selected for the study. The solubility of cyanuric acid in organic solvents used for the synthesis of quantum dots was evaluated; the flowability of the powder and the effect of exposure to solvents on it were analyzed. Samples of cyanuric acid powder marked with quantum dots with different luminescence peak positions and intensities were obtained. The luminescent properties of the obtained powders were investigated, the minimum amount of powder with quantum dots applied to the surface in the total composition sufficient for labeling was estimated, and the effect of applying quantum dots to the surface on the flowability of the powder was estimated. The possibility of marking bulk material with compositions of quantum dots with clearly defined monochromatic luminescence bands to create an invisible “fingerprint,” which is determined in laboratory conditions, is investigated.

The theoretical study of mechanical properties of the celecoxib (4-[5-(4-methylphenyl)-3-(trifluoromethyl)pyrazol-1-yl]benzenesulfonamide) form III crystal structure (space group P-1) has been carried out. For this purpose, increasing uniaxial deformations of the crystal structure along three axes of the crystal cell were simulated. To obtain the equilibrium structure of this crystal and structures under tensile strain, quantum-chemical calculations with periodic boundary conditions were performed by the DFT method at the PBE0/pob-DZVP2 level and by the HF-3c method with the following semiempirical corrections: Grimme dispersion correction (D3) for weak interactions, atom pair-wise geometrical counterpoise correction (gCP) for basis set superposition error, and correction for short-ranged basis set incompleteness effects (SRB). It was found that the analysis of stiffness tensor of only the equilibrium crystal structure did not provide the complete information about crystal mechanical behavior in different spatial directions, although this analysis made it possible to determine flexibility signs of the celecoxib structure in the (001) plane. In this case, the direction of maximal resistance of the structure to uniaxial deformation is not determined by specific intermolecular bonds and/or chains but is oriented almost parallel to the plane of conformationally rigid phenyl and pyrazole rings of the celecoxib molecule. The virtual tensile test has allowed to predict the manifestation of elastic properties of the celecoxib crystal in the (001) plane, up to 15% stretching along the crystallographic axes a and b. At greater strains along the a axis, a “non-healing” cavity is formed, which corresponds to the experimental observation of crystal transition to a brittle state. Analysis of the tensile test results confirmed the reliability of previously proposed brittleness/plasticity/elasticity signs for the prediction of dynamic mechanical properties, using the celecoxib crystal as an example.