Theoretical and Experimental Chemistry最新文献

The current state of research on non-conventional luminescence of unconjugated polymers, which is caused by the occurrence of through-space conjugation due to the overlapping of electronic orbitals of atoms in aggregates formed at high concentrations of substances in solutions or the solid state, is considered. The luminescent properties of different types of polymers containing oxygen, nitrogen, sulfur, silicon, boron, phosphorus is analyzed. The possibilities of the practical applications of polymer cluster luminophores in the fields such as ecosystem monitoring, medicine, biology, encryption, forensics, and optoelectronics are shown.

A new method of obtaining of antimicrobial coatings based on segmented polyurethanes and silver nanoparticles (SNP) stabilized by an ionic liquid is proposed. The effect of silver nanoparticles on the structure and characteristics of the obtained materials have been studied using X-ray scattering, electron microscopy, infrared spectroscopy, differential scanning calorimetry, and the microbiological method of diffusion in agar. It is established that in the polymer matrix, SNPs with sizes from 7 to 19 nm are formed, and their size depends on the content of the stabilizer. The obtained nanocomposite coatings exhibit high antimicrobial activity against bacteria (S. aureus, E. coli) and fungi (C. albicans).

An obtaining of sulfur nanoparticles by hydrothermal method in aqueous solution of L-cysteine, citrate ions, and sodium sulfide is proposed. The optical properties of the obtained sulfur nanoparticles have been studied by UV-Visible absorption and photoluminescence spectroscopies. Transmission and scanning electron microscopies and atomic force microscopy indicate that sulfur nanoparticles are quasi-spherical, their diameter depends on heat treatment time reaching an average size of 28 nm after 8 h of heating at 378 K. The nanoparticles exhibit photoluminescence in the range from 388 to 515 nm depending on the excitation wavelength. The obtained colloid systems have lasting sedimentation stability and high photoluminescence intensity, which make them promising for further wide application.

Film-like Ag₂O coatings have been obtained using electrochemical method, and their photoelectrochemical and spectral properties have been studied. The photocatalytic behavior of these samples in the process of reduction of carbon dioxide with water vapor has been studied. The possibility of formation of a number of organic compounds (acetaldehyde, acetone, isopropyl and ethyl alcohols, methane) upon irradiation of the systems with visible light has been established.

The peculiarities of the formation and stabilization of silver nanoparticles (NP) in the presence of quercetin and rutin during chemical (NaBH₄), thermal (at 90°C) and photochemical reduction of Ag⁺ ions have been studied considering the ratios of the components. It is shown that the reduction of Ag⁺ with the formation of silver nanoparticles with size of 50-90 nm occurs most efficiently in the presence of quercetin under the action of UV irradiation. The stabilization of Ag NP occurs due to complexation of flavonoid molecules with the silver ions on the surface of nanoparticles. The obtianed binary colloid composites flavonoid–Ag may be used in medicine as anti-inflammatory and bactericidal agents of prolonged action.

Semiconductor materials based on SnO₂ with different contents of cerium and stibium have been obtained. Their phase compositions, particle sizes and sensitivities of semiconductor sensors based on them to hydrogen have been studied. It is found that introduction of cerium into the material contributes to reduce the sizes of SnO₂ nanoparticles. Changes in the values of the sensor responses to hydrogen are explained by influence of catalytic activity of cerium and the competing effect of the introduced stibium on conductivities of the materials.

Solid solutions K₂Bi(PO₄)(MoO₄):Gd,Eu containing from 0.1 to 30 mole% of europium(III) and 0.1 mole% of gadolinium(III) have been prepared by conventional solid state reaction. The samples are characterized by X-ray powder diffraction method, IR and luminescence spectroscopies. It has been shown that doping with Eu³⁺ does not affect the symmetry of the layered framework. At room temperature, all the studied samples are characterized by intense red photoluminescence, which is associated with ⁵D₀→⁷F_0-4 emission transitions in Eu³⁺ ions. Due to the absence of concentration quenching and color characteristics, K₂Bi(PO₄)(MoO₄):Gd,Eu has prominent prospects for application as a red phosphor.

It is established that the effeciency of the hydrogen evolution from water–acetonitrile solutions of benzyl alcohol and a number of its derivatives under the action of visible light with the participation of crystalline graphite-like carbon nitride increases when electron-donating ability of the substituent in the para position of benzyl alcohol increases. The highest H₂ evolution rate, 720 μmol·h^–1·g^–1 (quantum yield Φ = 22% at 405 nm), is achieved in solutions of 4-methoxybenzyl alcohol in the presence of 0.1 M HCl at 40 °C.

It is shown that zinc oxide synthesized by combustion of jellied precursor forms well-crystallized micro-sized particles when treated at 600 °C. It is shown that these particles reveal high photocatalytic activity in rhodamine B dye and metronidazole degradation processes in an aqueous medium, exceeding the activity of commercial nano-sized samples of ZnO. The activity increase of the synthesized sample is connected with the presence of oxygen vacancies, which provides to formation of the charged oxygen species and OH groups on the oxide surface. The formation of zinc oxide microcrystals contributes to the separation of photogenerated charges and reduces the probability of their recombination.

The requirements for high-quality microwave (MW) dielectrics, which are used in the development of cellular communication devices (radio filters, solid-state generators, etc.) for the transition from 3G to 5G communication, are considered. The results of studies on important classes of MW dielectrics based on complex oxide systems of different crystal structures, such as potassium tungsten bronze, perovskite, pucherite, dreyerite, scheelite, as well as high-quality MW dielectrics with different permittivities, are systematized.