Russian Journal of Physical Chemistry

Catalysts based on nickel, cobalt, and platinum supported on carbon and silica gel were synthesized and studied. Energy-dispersive X-ray analysis (EDX) was used to evaluate the distribution of metals in the bulk phase. X-ray photoelectron spectroscopy (XPS) was employed to determine the atomic ratios in the near-surface layer. It was shown that the metal concentration on the surface can significantly differ from its content in the bulk. Metal distribution profiles from the surface to the interior of the catalyst granules were constructed. Textural characteristics of the studied catalysts were obtained. A method for determining the number of active sites on the catalyst surface based on EDX, XPS, and textural data was proposed. The calculated number of metal atoms was compared with the amount of reactive hydrogen adsorbed on the active sites. The results allowed evaluation of the influence of the synthesis method on the content of active sites on the catalyst surface.

A mullite precursor was synthesized via combustion of a xerogel obtained from a mixture of aluminum nitrate, highly dispersed silica (AEROSIL), urea as the fuel (reducing agent), and hydrogen peroxide as an auxiliary additive. The crystallization process of the precursor — its transformation into mullite 3Al₂O₃·2SiO₂ — was studied by thermal analysis, X- ray diffraction, IR spectroscopy, and NMR. The synthesized powder was amorphous and crystallized upon heat treatment at 1100 °C. Firing at 1200 °C yielded well-crystallized single-phase mullite. The combustion product contained AlO₄, AlO₅, and AlO₆ groups. Using thermal analysis of the precursor at different heating rates, the effective activation energy of mullite crystallization was estimated from the positions of the exothermic peaks corresponding to this transition.

A mechanochemical synthesis of silicon-oxygen-carbon composites was carried out using mixtures of activated carbon and silica gel in various mass ratios. The resulting materials were found to possess a uniform amorphous structure and well-developed porosity. It was shown that the acid-base surface properties are governed by phenolic, carboxyl, and silanol groups of different configurations, with the dominant contribution coming from groups with pK_a values of 8.5- 12. An increase in the concentration of these groups accompanied by a decrease in the concentration of groups with pK_a 0-5 leads to a higher pH at the point of zero charge. It was revealed that, due to electrostatic interactions, the synthesized composites adsorb methyl orange more effectively than methylene blue. The highest adsorption capacity toward methyl orange (286.2 mg/g) was observed for the sample obtained from the mixture with an activated carbon-to-silica gel mass ratio of 1:2.

Composite sorbents based on chitosan containing silica, Jerusalem artichoke powder, and carbon nanotubes were developed for the extraction of heavy-metal ions from aqueous solutions. The equilibrium and kinetics of Cu(II) ion removal in the heterogeneous system "aqueous metal sulfate solution - sorbent" were investigated for both the initial chitosan powder and the modified sorbents obtained in the form of hydrogel granules. The kinetic experiments established the time required to reach sorption equilibrium and identified the kinetic model that most accurately describes the process. The experimental sorption isotherms demonstrate a significant increase in the sorption capacity of the chitosan-based composites compared with the unmodified material. Processing the Cu(II) sorption isotherms using the Langmuir model allowed determination of the maximum sorption capacities (A_∞). It was found that A_∞ for the chitosan/silica/Jerusalem-artichoke composite and for the chitosan/carbon-nanotube composite substantially exceeds that of the original chitosan. Changes in the sorbent composition resulting from modification are confirmed by IR-spectroscopic data. SEM studies show a well-developed surface structure of the composite chitosan-based hydrogel granules.

This study explores the potential use of iron oxide powder — an industrial by- product from the manufacture of organic dyes — as a raw material for producing oxide catalysts. The physicochemical properties of the initial material and samples subjected to different types of treatment (mechanochemical activation, ultrasonic processing in oxalic acid solution) were investigated using X- ray diffraction, Mössbauer spectroscopy, scanning electron microscopy, and low- temperature nitrogen adsorption. It was established that optimal physicochemical characteristics are achieved through combined treatment: ultrasonic dissolution in oxalic acid followed by calcination at 425°C. Mechanochemical activation and ultrasonic processing enable the regulation of the composition and properties of the resulting oxides (substructural characteristics, dispersion, specific surface area, and porous structure). These processing methods allow for the formation of properties required for most catalysts used in the steam reforming of carbon monoxide and biomass pyrolysis.

The processes of electrodeposition of tin-nickel alloys onto steel grade 08kp from oxalate-ammonium electrolytes and the physicochemical properties of the resulting coatings were studied. It was shown that electrodeposition proceeds with high polarization, in contrast to the deposition of tin-nickel alloys from chloride-fluoride electrolytes. The highest corrosion rate (26 μA/cm²) was observed for the sample coated using the chloride-fluoride electrolyte. Low corrosion rates were recorded for samples coated with tin-nickel alloys containing low nickel levels and deposited from oxalate-ammonium electrolytes with the addition of reagent OS-20 (1.2- 5 μA/cm²). The influence of the alloy component ratio on the chemical composition and microstructure of the coatings was demonstrated.

The study presents an analysis of the patterns of photodestruction of acid azo dyes in aqueous solution. A fragment-based approach was employed, which decomposes the molecule of the organic compound into molecular fragments of connected atoms. This analysis allowed evaluation of the contribution of molecular substructure fragments to the logarithm of the first-order photodestruction rate constant of the dyes. The effects and directions of fragments with various sequences of connected atoms were analyzed. The photodestruction kinetics in solution were compared with the lightfastness characteristics of the dyes adsorbed on a natural keratin substrate. Similarities were found between several individual polyatomic fragments responsible for photodestruction in solution and those affecting lightfastness in the natural substrate.

A neodymium-lithium nickel-manganite of composition NdLi₂NiMnO₅ was synthesized via a solid-state reaction of Nd₂O₃, NiO, Mn₂O₃, and Li₂CO₃ in the temperature range 600 – 1250°C. X-ray diffraction analysis showed that the compound crystallizes in a cubic system. Calorimetric measurements in the 298.15–673 K range revealed the temperature dependence of the heat capacity, with anomalous jumps observed at 348 K and 423 K, likely associated with second-order phase transitions. The standard entropy was calculated. Thermodynamic functions S°(T), H°(T) – H°(298.15K), and Φ°(T) were determined over the 298.15–675 K interval. Electrophysical properties, including capacitance, electrical resistance, and dielectric permittivity, were studied in the 293–483 K range. It was found that NdLi₂NiMnO₅ exhibits p-type (hole) conductivity in the 293–363 K and 423–483 K ranges, while metallic conductivity occurs in the 363–423 K interval.

The Fenton reaction is of significant interest due to its applications in chemical, biochemical, and biomedical studies. It allows the assessment of hydroperoxide content in a sample. For such studies, it is necessary to know the reaction characteristics at different ratios of hydroperoxide and ferrous ion concentrations. The reaction yield is determined by measuring chemiluminescence. This work calculates the number of oxidation acts N(Fe²⁺ → Fe³⁺) in the Fenton reaction for the cases [Fe²⁺] > [H₂O₂] and [Fe²⁺] < [H₂O₂] with Fe²⁺ and H₂O₂ concentrations in the range 10⁻³ to 10⁻⁷ mol/L. It is shown that the hydroperoxide concentration can only be unambiguously determined when [Fe²⁺] > [H₂O₂]. In the case [Fe²⁺] < [H₂O₂], the strong decrease in reaction rate makes it difficult to register the full chemiluminescence output. The kinetics of the formation of luminescent products in the Fenton reaction were also calculated after the addition of luminol, which enhances the light emission.

The complex formation process in the system [ReOCl₅]^2- – O_x/Red – HCl (O_x – bis – N – ethyl formamide disulfide (H₂DEFds²⁺), Red – N – ethylthiourea (Etu)) was studied by potentiometric titration in the temperature range 273.1–338.1 K, and the lgK_i values of the complexes were determined. Using the lgK_i values, the thermodynamic parameters of the process (ΔH^°, ΔG^° and ΔS^°) were calculated. It was found that during the complexation of rhenium(V) with N-ethylthiourea, the exothermicity of the process decreases with increasing number of coordinated ligand molecules. It was revealed that the most favorable condition for the formation of stable complexes is a concentration of 4 mol/L HCl; i.e., when the hydrochloric acid concentration decreases from 6 to 4 mol/L, the stability of the resulting complexes increases.

The study focuses on the physicochemical regularities of the sorption of several heavy metal ions from aqueous solutions using a carbon–mineral sorbent based on rice husk. To understand and explain the sorption mechanism, the effect of pH on ion sorption was investigated. The change in sorption with successive increases in the solution-to-sorbent ratio was studied. A functional relationship α = f(V/m) was determined to predict the influence of the ratio on the extraction degree of metal ions by the obtained sorbent. Sorption isotherms were analyzed using known models (Langmuir, Freundlich, Redlich-Peterson, Dubinin-Astakhov, BET). It was found that increasing temperature decreases the sorption of these ions. Differential adsorption heats at various degrees of sorbent filling were calculated, allowing characterization of the energetic properties of its surface and the features of intermolecular interactions in surface layers. The kinetics of metal ion sorption and the time to reach sorption equilibrium were examined. Using Boyd and Morris-Webber models, the contributions of external and internal diffusion to the sorption process were analyzed. The results indicate that metal ion sorption on the obtained sorbent is a combination of physical sorption and chemical adsorption, with reversible specific interactions. It was shown that ions of this series exhibit different sorption capacities and interact differently with the sorbent surface depending on the conditions. The obtained sorbent can be effectively used for extracting trace concentrations of heavy metal ions from aqueous media.

Industrial samples of the second-generation rodenticidal substance Bromadiolone (I) have been studied by UV, IR spectroscopy, RP HPLC and X-ray diffraction. The conditions for the identification of the isomeric composition by the RP HPLC method were preliminarily selected, which made it possible to divide the studied samples of the substance into groups differing in isomeric (cis/trans) composition I in the range from 82:18 to 72:28 (in products up to 64:36). The aspects of sample preparation and the results of the analysis of various formulations/products containing I are presented. Two different crystalline phases I_a and I_b have been isolated from amorphous technical substances, characterized by a complex of physico-chemical methods (IR, XRD, DTA, PPM) and comparative efficacy data have been obtained. The crystal structure for I_b was determined by the pX-ray diffraction analysis method. An attempt to isolate I from various solvosystems based on dimethyl sulfoxide led to the crystallization of phases representing degradation and rearrangement products. Under production conditions, when heated in this particular solvent, highly concentrated forms (premixes) I are obtained, which are used to prepare poisoned rodenticidal baits. Analysis of the XRD data showed that the rearrangement products, in addition to the expected salicylic acid, were cyclic derivatives: triacetone triperoxide and γ-butyrolactone II with volume substituents in the 3rd and 5th positions. Direct synthesis of II, due to the presence of bulky substituents, is difficult, however, as it turned out in the course of the work, it can be realized by directed rearrangement of I. Apparently, homologues of γ-butyrolactone with other substituents can be obtained using substances related to bromadiolone.