Theoretical and Experimental Chemistry最新文献

The acidity and basicity of MFe₂O₄ (M(II) = Fe, Mg, Mn, Zn) ferrites of the spinel structure have been characterized by temperature-programmed desorption of NH₃ and CO₂. It is shown that both medium-strength basic and acid sites play an important role in the process of acetone obtaining from ethanol over ferrites. The selectivity of ethanol conversion to acetone depends both on the acid–base properties of the surface and on the ability of the surface oxygen of ferrite to participate in the intermediate redox stages of formation and steam reforming of acetone.

To create highly sensitive semiconductor hydrogen sensors, nanosized tin dioxides with particle sizes of 5-6 and 10-11 nm have been obtained by the sol-gel method using various precursors, as well as Pd-doped materials on their base. The maximum sensitivity to the hydrogen microconcentrations has been found for the sensors based on the nanosized ex-oxalate SnO₂ containing 0.24% palladium. High sensitivity of the obtained semiconductor sensors is explained by the significant influence of surface processes on their electrical resistance due to the smallest sizes of the SnO₂ particles.

The formation of supramolecular complexes of 3-methyl-sulfido-propoxycalix[4]arene-methylene-bis-phosphonic acid with seventeen amino acids in aqueous solutions has been studied and their stability coefficients have been determined by the method of high-performance liquid chromatography. The structures of the supramolecular complexes have been proposed by molecular modeling and the influence of structural factors (the stabilization of different conformations of the obtained complexes depending on amino acid nature: possibilities of the realization of hydrogen bonds and electrostatic interactions between different groups of the amino acids and calixarene) on the stability of the supramolecules has been shown.

VO_x/SiO₂ with different V/Si atomic ratios have been synthesized by hydrothermal method from alkoxides of vanadium and silicon compounds. The prepared samples are characterized by high specific surface area (300-700 m²/g), uniform nanodispersed distribution of vanadia in silica matrix, the absence of crystalline phases, and the absence of the band typical for V=O bond in the Raman spectra. High activity and selectivity of the synthesized catalysts in oxidation of methane to formaldehyde, oxy-dehydrogenation of propane and n-butane have been established.

Superacid (H₀ ≥ –14.52) ternary Zr₃₅Si₅₃Al₁₂ and Zr₂₁Si₆₇Sn₁₁ oxides have been studied by X-ray photoelectron spectroscopy. The high-energy shifts of Zr3d levels indicate the electron density shift from zirconium to silicon atoms, which is facilitated by the presence of tetrahedrally coordinated Al³⁺ and Sn⁴⁺ ions in Zr⁴⁺ environment. Models of the superacid L-sites that include coordinatively unsaturated zirconium ions are proposed.

The current state of research on photocatalytic systems for hydrogen production by metal carbides is considered. Approaches for obtaining of known and latest two-dimensional metal carbides (MXenes) and their composites with the participation of photoactive semiconductors or organic dyes are described. Properties of these materials such as photocatalysts, and precursors used in their obtaining or co-catalysts used in hydrogen production systems where metal carbides act as acceptors and carriers of photogenerated charges or catalysts of the hydrogen evolution reaction are analyzed. The most promising areas of further research are outlined.

Specific features of the localization of coumarin and xanthene dye molecules in ionic surfactant micelles of sodium n-dodecyl sulphate and cetyltrimethylammonium bromide have been studied by molecular dynamics simulation. It is shown that the change in the microenvironment of a dye molecule in a micelle after its protonation (deprotonation) depends on both the nature of such a dye and the sign of the micelle charge. It was established that the presence of a long hydrocarbon chain in a dye molecule does not prevent its movement during (de)protonation.

Samples of nanocrystalline graphite-like carbon nitride (CGCN) modified with magnesium chloride have been obtained. The synthesized Mg-CGCN samples have been characterized by UV and IR spectroscopies, X-ray diffraction, energy dispersive X-ray analysis, and scanning electron microscopy. It is found that Mg-CGCN exhibits 60% higher photocatalytic activity in the reaction of hydrogen evolution from aqueous ethanol solutions under visible light than undoped CGCN. This may be related to a change in electrophysical characteristics (potentials of allowed bands) resulting from the incorporation of Mg²⁺ ions into the CGCN structure, improved dissociation of photogenerated charges, and inhibition of their recombination.

CoL₃·DMF, [CoCdCl₂L₃]·0.5H₂O, and [CoMnCl₂L₃]·H₂O complexes, where HL is a product of the condensation of o-vanillin and methylamine have been obtained. The crystal structure of the latter complex has been determined by X-ray structural analysis. The study of the antioxidant activity of these complexes in a model reaction of radical-chain oxidation of benzyl alcohol with an atmospheric oxygen has proved a significant inhibition of this process at concentrations of the complexes of 10^–7-10^–6 mol/L. It is established that the inhibitory activity of the compounds depends on the nature of the metal ions present in the complex.

Foam-like binary Cu₂O/Ag₂O nanoheterostructures have been obtained by an electrochemical method. Their photoelectrochemical and spectral properties have been studied. The photocatalytic properties of these composites in the process of gas-phase reduction of carbon dioxide with water vapor have been studied. The formation of binary nanoheterostructures leads to an increase in methane yield and an increase in the amount of other organic products (acetaldehyde, ethylene, and ethanol) while the system is irradiated with visible light when compared to Cu₂O. This effect can be explained by the formation of a nanostructured Cu₂O/Ag₂O binary composite with a mutually consistent energy profile.