Russian Journal of Physical Chemistry A最新文献

DFT modeling of lithium adsorption and intercalation processes was carried out for various configurations of graphene-like structures containing defects such as single vacancies and nitrogen doping. It was found that vacancies reduce the adsorption energy by forming stable binding centers. In nitrogen-doped systems, the adsorption energy remains stable with increasing lithium concentration. Intercalated structures exhibit a decrease in stability with an increasing number of lithium atoms, especially in the case of nitrogen doping, which is accompanied by deformation of the graphene layers.

The binary and more complex metallic melts are characterized by instability of composition along the height of the melt. After having been kept for a short time in a vertical nonwetted vessel (crucible or capillary), the initially homogeneous melt acquires a gradient of component concentrations along the height, and the heavy component is distributed along the height of the crucible according to the barometric distribution of large particles (clusters). This is one of the factors responsible for the cluster structure of melts. An analysis of the experimental results leads to the conclusion that there is a second mechanism of mass transfer in liquid metals, namely, the transfer of atoms in the interphase monatomic layer at the boundary between the melt and capillary wall, which occurs simultaneously with diffusion. A number of special experiments clearly confirm this hypothesis. The experiment showed that the choice of orientation for the distribution channel of the melt components relative to the direction of the gravitational field makes it possible to isolate both mechanisms practically in “pure form,” and there is evidently no other way to explain the results of the experiment.

An approach is proposed that can allow ab initio solution of the phase problem in X-ray diffraction studies. A synthetic diffraction data generator has been created that can be used to solve applied problems using machine learning. An automated container is presented that allows reproducible experiments aimed at solving the problem within the framework of the proposed approach. The FFT_UNet and XRD_Transformer models were developed, taking into account the physical specifics of the problem, and a comparative analysis and interpretation of their work on real data were carried out.

It is shown that the group and individual composition of A-92 motor gasoline can be determined on a PTMSP025 capillary column with a poly(1-trimethylsilyl-1-propyne) (PTMSP) stationary phase. It was found that the PTMSP column is characterized by the order of elution similar to that for capillary columns with porous organic polymers. Hydrocarbons are eluted in groups according to the number of carbon atoms in the molecule. Alkenes are eluted first in the group, and then alkanes are eluted. This order of hydrocarbon retention on the PTMSP025 column allows a more structured pattern of separation compared to the column with the polysiloxane stationary phase. Methyl-tert-butyl ether (MTBE), used as an octane booster, is determined on a PTMSP025 column without an additional sample preparation (concentration) step. The possibility of separating gasoline components using comprehensive two-dimensional chromatography was also demonstrated, where a PTMSP025 column was installed in the first dimension, and a column with dimethylpolysiloxane as a stationary phase in the second.

A systematic density functional theory (DFT) study has been performed to assess structures, stabilities and electronic properties of small Ni_xMo_y (x + y ≤ 6) clusters. The lowest energy structures have been determined by testing several possible geometries at the PBEPBE/SDD level of theory. The results suggest that the tetramer, pentamer and hexamer clusters prefer three-dimensional (3D) configurations. The dimers and pure Mo clusters are found to be more stable as compared to other clusters. Also, the NiMo dimer possesses the highest chemical reactivity among the examined clusters. The calculated vertical ionization potential (VIP) and vertical electron affinities (VEA) values of the clusters show their tendency towards accepting electrons. The natural bond orbital (NBO) analysis suggests that a charge transfer takes place from Mo atoms to Ni atoms within the NiMo and Ni₂Mo clusters, and vice versa in the Ni₃Mo, Ni₄Mo, and Ni₅Mo clusters. The H₂ adsorption on the Ni_x (x = 2–6) and Ni_xMo (x = 1–5) clusters has also been investigated. The results suggest that the hydrogen dissociation form is more favorable as compared to the molecular adsorption. Hydrogen atom tends to draw electrons from the metal cluster in the dissociative form of the Ni_xH₂ systems, while donate electron to the metal cluster in the molecular adsorption form. In the Ni_xMoH₂ clusters, electron donation occurs from the metal cluster to the hydrogen atom. The transition pathway from the H₂ molecular to dissociative adsorption on the NiMo and Ni₂ clusters has also been evaluated.

Hexaaluminates EuMg_0.8Al₁₁O_18.8 and GdMg_0.8Al₁₁O_18.8 with a magnetoplumbite structure were prepared by the citrate sol-gel method and identified by X-ray diffraction analysis, scanning electron microscopy, and EDX-spectroscopy. The enthalpies of formation of EuMg_0.8Al₁₁O_18.8 and GdMg_0.8Al₁₁O_18.8 from oxides and elements at 298.15 K were determined from the enthalpies of solution in molten lead borate.

Extensive research has been conducted for the oxidation of cinnamyl alcohol by thallium(III) in aqueous acidic medium with or without ruthenium(III) catalyst through an integrated kinetic, mechanistic, and computational (DFT) approach to explore the effect of catalyst in the oxidation rate. Kinetic investigations indicate that, without a catalyst, the reaction exhibits a first-order dependence on both cinnamyl alcohol and thallium(III), as well as an inverse dependence on hydrogen ion concentration. This implies the participation of a neutral or deprotonated form of the alcohol, and the bimolecular interaction between TlOH²⁺ and cinnamyl alcohol constitutes the rate-limiting step. But in the presence of the ruthenium(III) catalyst, the system exhibits first-order dependency on both thallium(III) and the ruthenium(III) while demonstrating a variable order concerning cinnamyl alcohol, suggesting a dual-pathway mechanism that incorporates both catalyzed and uncatalyzed processes. The changing order in alcohol indicates the formation of a pre-equilibrium complex between the alcohol and the catalyst. The observed results signify the concurrent participation of all three species in the rate-determining phase. This exemplifies a ternary transition state, in which cinnamyl alcohol establishes a temporary coordination complex with Ru(III), thereafter interacting with thallium(III) to promote electron transfer. The activation parameters derived from Eyring plots for each reaction imply different mechanistic pathways. The catalyzed pathway exhibits increased reactivity and diminished activation barriers, whereas the uncatalyzed route proceeds at a slower rate. Density Functional Theory investigation signifies the existence of a termolecular transition state involving cinnamyl alcohol, thallium(III), and the ruthenium catalyst, accentuating the catalyst’s role as a redox mediator that expedites electron transfer. The novelty of the research lies in the detailed mechanistic understanding of thallium(III)-catalyzed cinnamyl alcohol oxidations in aqueous media with or without ruthenium(III) catalyst supported by the computational analysis and in describing the substantial impact of catalytic intervention on activation parameters and reaction pathways and providing essential insights for the development of effective catalytic oxidation systems.

The mechanism and kinetics of [FeTMDTA(OH)]^2–’s (TMDTA = trimethylenediaminetetraacetic acid) interaction with cyanide ions have been investigated using spectrophotometry at 393 nm (the λ_max of [Fe(CN)₅OH]^3–) by monitoring a spike in absorbance. The specified conditions of reaction are; T = 298 K, ionic strength, I = 0.2 M (NaClO₄), and pH 10.5. The findings indicate that the reaction comprises three distinct phases; the initial phase involves the generation of [Fe(CN)₅OH]^3–, the subsequent phase entails the transformation of [Fe(CN)₅OH]^3– into [Fe(CN)₆]^3–, and the final phase involves the interaction of [Fe(CN)₆]^3– with the ligand (TMDTA) released in the initial stage, resulting in the formation of [Fe(CN)₆]^4–. The interaction of [FeTMDTA(OH)]^2– with CN^– exhibits a variable order dependency on [CN^–] during the initial stage, fluctuating between one to three at elevated and diminished [CN^–]. The subsequent phase of the process exhibits a first-order reliance on both [CN^–] and [Fe(CN)₅OH^3–]. The last stage of the reaction adheres to a general second-order kinetics, exhibiting first-order characteristics with respect to both [Fe(CN)₅OH^3–] and [TMDTA^4–]. Studies have also examined the thermodynamically disadvantageous reversed reaction of [Fe(CN)₅OH]^3– with TMDTA^4–, which is merely driven by a substantial excess of TMDTA^4–. The reverse reaction demonstrates an inverse first-order reliance in [CN^–] and first-order dependences in [TMDTA^4–] and [Fe(CN)₅OH^3–]. The fourth step of the recommended mechanism, which is the rate-determining step, is further supported by the forward reaction rate’s dependency on ionic strength. The suggested mechanistic scheme is further substantiated by the activation parameters of both the inverse and forward reactions during the initial stage of the reaction.

The geometry of a plasma microwave resonator for CVD diamond growth technology was calculated using the Comsol package, which provides the growth of both an undoped diamond in the TM mode and of the doping δ layer in the TE mode. It is shown that sufficiently homogeneous plasma over the diamond growth surface (substrate) can be maintained in the TE mode at a low gas pressure that is optimal for growing the δ layer. The main trends predicted by the simple calculation model developed in the first part of the present communication, in particular, sufficiently high electron temperature and plasma density when using the low-pressure TE mode, are confirmed.

The degree of asymmetry of the excess surface tension (σ) isotherms of boundary binary systems was found to be the main criterion for preliminary assessment of the applicability limits of the Kohler method. For quantification of the degree of asymmetry of the excess surface tension isotherms of binary systems, we used characteristics of the distribution of a random variable (asymmetry coefficient, excess). The surface tension and asymmetry coefficients in boundary binary systems were calculated for 12 ternary systems for which reliable experimental data were available. The ternary systems can be divided into several groups according to the average asymmetry coefficient of two boundary binary melts: insignificant asymmetry (the average value of the asymmetry coefficient is smaller than 0.7; the σ values obtained by the Kohler method coincide with the experimental data within the measurement error); moderate asymmetry (the average value lies in the range from 0.7 to 0.8; the σ isotherms qualitatively describe the experimental curves); and significant asymmetry (the average value is greater than 0.8; the theoretical curves do not describe the experimental curves).