Vol 69, No 4 (2024)

The results are summarised of the Seventh International Conference of CIS countries “Sol-gel synthesis and research of inorganic compounds, hybrid functional materials and disperse systems “Sol-gel 2023”, the key reports are discussed within the scientific sections: Theoretical aspects of sol-gel process; Films, coatings and membranes obtained using sol-gel technology; Hybrid organic-inorganic sol-gel materials; Xerogels, glasses and bulk ceramic materials synthesized by sol-gel method; Nano- and microstructured materials, nanotechnology; Methods of research of structure and properties of materials obtained using sol-gel synthesis.

This work describes the use of silica particles obtained by sol-gel method as a templat for deposition of supramolecular complexes of melamine cyanurate. To obtain SiO₂@melamine-cyanurate (SiO₂@MCA) material, the method of covalent modification of silica surface by melamine molecules (SiO₂-mel) was applied and the method of its further functionalization by hydrogen-bonded organic framework of melamine-cyanurate (HOF, MCA) was proposed. One of the promising directions of using SiO₂@melamine-cyanurate is obtaining SiO₂@g-C₃N₄ material on its basis. Control of the amount of applied melamine-cyanurate allows to potentially obtain g-C₃N₄ layers of different thicknesses on the silica surface.

Ru-containing hydrogenation catalysts based on functionalized carbon material CMK-3 (Carbon Mesostructured by KAIST) were developed. Mesostructured silicate SBA-15 with enlarged wall channels was used as a template for the carbon replica synthesis. The effect of carbon material functionalization via moist air oxidation and sulfonation on the morphology, physicochemical properties and activity of the catalyst was studied. The dispersion, localization, and electronic state of supported ruthenium were determined depending on the support functionalization method. The initial support structure preservation after Ru deposition was confirmed by a set of physicochemical methods. Metal particles are finely distributed with no agglomerated present, providing a high active site accessibility and ensures a superb catalyst activity. The catalysts were tested in glucose to sorbitol hydrogenation. The results showed that pore morphology and carbon support initial structure preservation account for the catalytic activity of Ru nanoparticles.

In this research, the electronic states, band structures, and bond properties of the framework compounds of CoPO₄, Co_1-xFe_xPO₄, and Co_1–xNi_xPO₄ were investigated by the density functional theory calculations. The potential capabilities of these systems in the photocatalytic water splitting to produce hydrogen were analyzed. The spin-up electron densities of states for the CoPO₄, Co_1–xFe_xPO₄, and Co_1–xNi_xPO₄ systems have band gaps of 2.7, 3.4, and 3.45 eV, respectively. The band of spin-down electron states has several energy gaps above the Fermi level. The density of states of electron with spin up near the Fermi level is obviously greater than that of electrons with spin down. In this case, localized states of electrons appear in the band gap of doped semiconductors due to impurity atoms. The calculated value of the energy at the lower edge of the conduction band for CoPO₄ was –0.7 eV, which is more negative than the energy required for water splitting. Meanwhile, the calculated value of the energy at the upper edge of the valence band was 2.01 eV, which is more positive than the oxygen evolution energy of 1.23 eV.

The complexation process of tolane and α-cyclodextrin in water, aqueous-ethanol solution and silicate hydrogel based on tetrakis(2 hydroxyethyl)orthosilicate was studied. The complex formation in solutions were confirmed by electron and ¹H NMR spectroscopy, and the stability constant of the complex was determined using spectrofluorimetric titration (lgK_1:1 = 1.5). The preservation of the inclusion complex during the preparation of the gel was confirmed by electron spectroscopy.

This study is devoted to the preparation of strong spherical composites V₂O₅/TiO₂–SiO₂ by a combined template and sol-gel method. The composition, size and shape of the colloidal particles in butanol ash with tetrabutoxytitanium and tetraethoxysilane, as well as the physicochemical processes leading to the strengthening of the spherical agglomerates obtained using an anion exchanger with a gel structure, have been determined. Electrophoresis, small-angle X-ray scattering, and viscometry were used to demonstrate the presence in the sol of positively charged colloidal particles of lenticular and cylindrical shape, whose size, when the sol is stabilised, reaches 53 Å. The absorption of the sol by the anion exchanger in vanadium form is due to the equalisation of the osmotic pressure in the anion exchanger/sol system. Spherical composites with a diameter of 300 µm were obtained. It was shown by X-ray diffraction that the composites consist of V₂O₅ with an orthorhombic structure, TiO₂ with an anatase structure, and amorphous silicon dioxide. The interaction at the interface between the phases of V₂O₅ with TiO₂ and SiO₂, which leads to the strengthening of the sphere of the V₂O₅/TiO₂–SiO₂ composite, has been demonstrated by IR and Raman spectroscopy. The results obtained can be used for the synthesis of M_xO_y/TiO₂–SiO₂ oxide composites with spherical agglomerates.

In order to use the β-cyclodextrin-pyrene complex as a fluorescent receptor center, its stability in the solid phase of a water-soluble silicate gel was investigated. For this purpose, a technique for obtaining a silicate matrix with a high content of supramolecular complexes was developed and the temperature stability of the resulting material was investigated. Optimal conditions for working with complexes in the silica gel matrix have been identified. Comparative studies of the fluorescence spectra of complexes in liquid and solid phases were carried out by the method of fluorescence spectroscopy. As a result of the work done, it was possible to determine the main patterns of behavior of the supramolecular complex in the silicate hydrogel matrix and to conclude about the influence of the matrix structure on its stability.

Anemia is a prevalent circulatory system illness that is severely harmful to patients. The development of novel oral delivery systems for iron compounds with enhanced biopharmaceutical properties is vital considering the severe side effects associated with oral medication use. We believe incorporating iron compounds to polymethylsilsesquioxane hydrogels is a promising approach. According to previously published materials, such a system should have great biocompatibility and a capacity for iron compounds, and it may be able to release contents into the intestine. This study investigated polymethysilsesquioxane hydrogels with varying silicate unit concentrations. Potential iron-containing medicines were iron(III) chloride (FeCl₃∙6H₂O)) and iron(II) D-gluconate. All hydrogels were found to have nearly 100% sorption activity for a saturated solution of FeCl₃∙6H₂O (0.27 M) during the experiment, but only around 30% sorption capacity was found for a saturated solution of D-gluconate (0.24 M). A specific field of study was the distribution of iron atoms within hydrogels. It has been established that the largest regions devoid of iron atoms are observed in a hydrogel with a maximum quantity of inorganic units. The outcomes provide opportunities for the precise engineering of polymer matrix structures for iron compound delivery.

The influence of the nature of MF-HCl etching systems (M = Li⁺, Na⁺, NH₄⁺) on the process of synthesis of Ti₃C₂T_x MXenes on the basis of Ti₃AlC₂ MAX-phase, microstructure, phase purity, interlayer distance, composition of functional surface groups, thermal behavior and yield of the obtained products has been studied. The room temperature sensing properties of Ti₃C₂T_x receptor layers deposited by microplotter printing were studied with respect to a wide range of gas analytes (H₂, CO, NH₃, NO₂, NO₂, O₂, benzene, acetone, methane and ethanol). Increased sensitivity to ammonia was revealed for the MXenes obtained by exposure to hydrochloric acid solutions of sodium and ammonium fluorides and to carbon monoxide for the sample synthesized using the LiF-HCl system. High responses (~20–30% to 100 ppm NO₂) were observed for all three receptor materials, but sensor recovery processes were significantly hampered. To improve the sensing characteristics, Ti₃C₂T_x sensing layers were subjected to relatively low-temperature heat treatment in an air atmosphere to form Ti₃C₂T_x/TiO_x nanocomposites. It was found that a high and selective oxygen response at very low operating temperatures (125-175°C) was observed for the MXenes partially oxidized, which is particularly characteristic of the material produced using the HCl-NaF system.

A method for the preparation of nanocomposite containing Ti_0.2V_1.8CT_x MXene core and titanium-doped vanadium oxide surface layers as a result of relatively low-temperature partial oxidation of MXene multilayer - two-dimensional vanadium-titanium carbide has been developed. It is shown that during oxidation in air atmosphere of initial Ti_0.2V_1.8CT_x at temperature 250°С, in general, the microstructure of accordion-like aggregates with some increase in porosity of their constituent layers and increase in their thickness due to the formation of V₂O₅ is preserved. At the same time, preservation of the MXene structure with a decrease in the interplanar spacing from 10.3 (initial powder Ti_0.2V_1.8CT_x) to 7.3 Å was observed. Raman spectroscopy confirmed the formation of vanadium oxide. Kelvin-probe force microscopy data revealed that the formation of Ti_0.2V_1.8CT_x/V₂O₅ nanocomposite results in a decrease in the work function from 4.88 (Ti_0.2V_1.8CT_x) to 4.68 eV. The chemosensor properties towards a range of gaseous analytes (H₂, CO, NH_3, NO₂, C₆H₆, C₃H₆O, CH₄, C₂H₅OH and O₂) have been comprehensively studied for Ti_0.2V_1.8CT_x/V₂O₅ layers coated using the microplotter printing. At increased detection temperatures (125–200°С), high sensitivity to oxygen (10% O₂) and NO₂ (100 ppm) is observed; there are notable responses to humidity (50% RH) throughout the 25–200°С temperature range. At room temperature, good response to acetone, ethanol and ammonia is observed.