Theoretical and Experimental Chemistry最新文献

Nanosized TiO₂/ZrO₂=1:1 composites have been obtained by mechanochemical, ultrasonic, and coprecipitation methods. It is shown that mechanochemical and ultrasonic treatments of a TiO₂ and ZrO₂ mixture lead to size reduction of oxide particles, changes in X-ray diffraction spectra, the formation of a mesoporous structure of TiO₂/ZrO₂ samples, and an increase in their photocatalytic activity in the reaction of Gesagard (prometryn) herbicide destruction in an aqueous medium when compared to a mechanical TiO₂ and ZrO₂ mixture. It is found that the sample obtained by coprecipitation is X-ray amorphous with a well-developed surface, however, it is significantly inferior to samples obtained by alternative methods in terms of photoactivity.

The electronic and spatial structure of 3,4-ethylenedioxythiophene oligomer containing 12 units (E12) in 0, +1, +2, +3, and +4 charge states has been calculated by the method of density functional theory (B3LYP 6-31 G**). It is shown that electron conductivity in the oxidized oligomer E12⁴⁺ is provided by two bipolarons at the ends of the chain.

The peculiarities of propane dehydrogenation with carbon dioxide over zeolite catalysts of different structural types, in particular, BEA with incorporated Zn, Ga (Ta, Nb) heteroelements have been analyzed. The role of CO₂ as an oxidant, the effect of acid–base characteristics on propylene selectivity and yield, the stability of catalyst operation, and the routes of activation of reagents on acid–base sites of the surface are considered.

A comparative study of electrochemical properties of mono- and few-layer samples of nitrogen-doped graphene as nanosized sensor materials for the qualitative and quantitative determination of dopamine and uric acid has been performed. It is found that the few-layer graphene (NGr(f)) is characterized by high sensibility to dopamine, while monolayer one (NGr(m)) is characterized by high sensibility to uric acid in presence of considerable concentrations of ascorbic acid. XPS results show that the nitrogen content is 8.3 at.% in NGr(f) and 6.2 at.% in NGr(m). The analysis of Raman spectra allows to establish, that NGr(f) and NGr(m) have a defective structure. NGr(f) is characterized mainly by edge defects, while NGr(m) is characterized by vacancies, what obviously predetermines the differences in electrochemical properties of these materials.

A method of synthesis of oligomeric siloxane protic ionic liquids capable of condensation reactions has been developed as starting compounds in the obtaining proton exchange membranes for fuel cells. Their organic frame is characterized by a combination of amine centers of different basicity (aliphatic and imidazole types) neutralized with ethanesulfonic acid and secondary hydroxyl groups. A change in the degree of neutralization of the amine centers significantly affects the structure of the compounds and the mechanism of proton migration. The conductivity of the obtained compounds reaches 9.8·10^–4 S/cm at 100°C in the absence of moisture.

Effective catalysts of CO₂ hydrogenation towards methane were obtained by impregnation of aluminum oxide with cobalt and iron nitrates. The catalysts have been characterized by XRD, SEM-EDX, argon physisorption, and TPD with mass-spectroscopy analysis. It is shown that an increase in the amount of applied Co-Fe active mass in the composition of a nanocomposite catalyst leads to an increase in the CO₂ conversion and CH₄ yield.

The main prerequisites necessary for the construction of molecular motors, in particular, organic compound-based light-driven motors, are considered and universal requirements for their operation are formulated. Various types of Brownian motors differing in the forms of directed motion are analyzed. Development prospects and molecular design strategies are provided for such nanodevices.

The theoretical principles of a spin transition phenomenon in pseudo-octahedral iron(II) complexes are summarized. The intrinsic transfer of electrons between d-orbitals of a central ion under the action of external factors and the corresponding changes in the structural, spectral, and magnetic characteristics of matter are considered. Cooperative interactions that lead to the appearance of hysteresis of physical properties have been studied in detail. Perspective areas of practical applications of compounds with spin transitions have been provided.

According to the analysis of literature data and our experimental results, a kinetic equation for the low-temperature conversion of carbon monoxide with water vapor over a highly active copper–zinc–aluminum oxide catalyst is proposed. It is shown that the obtained kinetic parameters can be used to calculate the reaction rate and optimize the process.

MnNaW/SiO₂ oxide system based on a mesoporous silica matrix synthesized using tetraethoxysilane and cetyltrimethylammonium bromide as precursors were prepared and characterized by SEM/EDS, XRD, EPR, N₂ adsorption-desorption measurements and studied in the oxidative conversion of methane (OCM). It is shown that MnNaW/SiO₂ catalyst consists of MnO_x, Na₂WO₄, MnWO₄, and SiO₂ phases. At the reaction temperature of 750-850°C the molten Na₂WO₄ phase covers the surface of crystalline SiO₂, and the interaction of MnO_x, Na₂WO₄ and SiO₂ matrix forms “liquid glass”. It is assumed that Na_1–yMnO_x particles formed as a result of the interaction of the system components during catalyst formation and characterized by the presence of ion-radical lattice oxygen are catalytically active sites in the OCM process.