Theoretical and Experimental Chemistry最新文献

The dependence of the electrochemical characteristics of layered cathode materials LiNi_xMn_yCo_zO₂ (0.4 ≤ x ≤ 0.6; y = 0.2, 0.3; z = 0.2, 0.4) on the method of applying a protective layer of nanoparticles of lithium-conductive material Li_1.3Al_0.3Ti_1.7(PO₄)₃ with NASICON structure onto their surface has been investigated. It is shown that the surface modification reduces the capacity fading during prolonged charge/discharge cycling (up to 15%) and improves the suitability for fast charge/discharge processes.

Comparative analysis of the sorption ability of the obtained carbonate forms of layered double hydroxides with different Ni(II)/Fe(III) ratio and their magnetic nanocomposites toward ({{text{UO}}}_{2}^{2+}) ions in aqueous solutions is performed. The synergistic effect of magnetic composite sorbents based on layered double hydroxides and magnetite on the removal uranyl ions in a wide pH range (3.5-9.5) is shown. Due to the high efficiency in combination with magnetic solid-phase separation, the obtained adsorption materials are promising for the purification of uranium-containing natural and wastewaters.

The current state of research on photocatalytic reforming of organic substances of natural origin using graphite-like carbon nitride, namely its various morphological forms, products of modification by chemical agents, doped with metals and non-metals, nanocomposites with metals and other semiconductors, etc., is considered. Reactions that lead to molecular hydrogen evolution from aqueous solutions of electron-donating organic compounds (lignocellulose, saccharides, alcohols, aldehydes, and acids), processes of simultaneous production of H₂ and oxidation of biomass components with the formation of valuable organic substances, as well as reactions of a reduction of several aldehydes of natural origin are analyzed. Possible ways of further research in this photocatalysis branch are outlined.

It is established that crystalline graphite-like carbon nitride (CGCN) exhibits high photocatalytic activity in the process of chemoselective reduction of furfural to furfuryl alcohol in the presence of co-catalysts under the action of visible light by electron-donating substrates, such as methanol/water and ethanol/water, in an acidic medium. When palladium chloride additives are introduced into the reaction mixture, the rate of the process is higher than with the participation of the Pd/SiO₂ co-catalyst. This phenomenon may be due to the in situ formation of the CGCN/Pd⁰ composite photocatalyst in the presence of PdCl₂, where the photogenerated charges are better separated than in the CGCN-Pd/SiO₂ system. The effective quantum yield of furfural reduction is 56% at λ_irr = 405 nm) under optimal conditions.

The conversion of dihydroxyacetone solution in methanol to methyl lactate has been studied in flow regime using xSnO₂/Al₂O₃-supported catalysts that have been characterized by XRD, low-temperature nitrogen (ad)desorption analysis, and UV-Vis spectroscopy. It is found that Lewis and Brønsted acid sites of the surface of SnO₂-containing catalysts play a crucial role in the selective conversion of dihydroxyacetone to methyl lactate. The formation of methyl lactate with a selectivity of 90% is achieved on 5%SnO₂/Al₂O₃ catalyst at 160°C, 1.0 MPa, and under feed rate of 4 mmol C₃H₆O₃/(g_cat·h).

By using a fractal approach, it is found that the irregular structure of the surface of titanium dioxide-based catalyst has a significant effect on the values of the rate constants and activation energies of the reaction of dehydrogenation and dehydration of ethanol, n-propanol, and iso-propanol. Kinetics of ethyl and propyl alcohol conversions on titanium dioxide samples with different textures and morphologies is studied. Dependencies of activation energy and pre-exponential factor of the reaction rate on the alcohol conversions on the TiO₂ samples on their structural characteristics, particularly a fractal dimension, are established.

Codoped C,S-TiO₂ nanostructures with similar structural and dimensional characteristics and different surface acidity have been obtained using a hydrothermal sol–gel method in the presence thiourea or sulfuric acid. It is established that C,S-TiO₂ obtained in the presence of H₂SO₄ are characterized with acidity of 0.45 mmol/g that results in a high photocatalytic activity in the process of ethanol oxidation. It is shown that C,S-TiO₂ obtained in the presence of thiourea, exhibits photocatalytic activity in the reaction of hydrogen evolution under UV and visible light irradiation, which increases with surface acidity decreasing.

Strontium and barium titanates with a perovskite structure have been obtained using a sol–gel method. It is shown that these materials are characterized by high values of a band gap (3.1 and 3.2 eV for SrTiO₃ and BaTiO₃, respectively). Morphological characteristics of the obtained titanates are considered, the presence of micrometer aggregates, consisting of nanosticks (diameter of 20-40 nm, length of 100-200 nm) and nanocrystals with size of 20-70 nm, is established. The photocatalytic properties of the samples in the process of NO₂ decomposition to N₂ and O₂ under UV irradiation (λ = 365 nm) are studied, a possible mechanism of nitrogen dioxide conversion is discussed.

Complexation of a copolymer of styrene and 5-methyl-5-hexene-2,4-dione with cobalt chloride in dimethylformamide occurs with the formation of metallopolymers of two types, namely with intra- and extramolecular binding of β-diketone groups, the ratio of which depends on the concentration of the initial macromolecular ligand. It has been established that the polymer metal complexes differ in the geometry of the coordination unit, molecular weights, and metal content resulting in the different reactivity to initiation of graft radical polymerization of methyl methacrylate.