Vol 68, No 12 (2023)

Phosphates Li1 + xTi1.8 – xFexGe0.2(PO4)3 (x = 0.1–0.3) with the NASICON structure have been prepared and studied for the first time. It has been shown that co-doping with germanium and iron leads to significant increase in the ionic conductivity of the prepared materials at low degrees of titanium substitution. The influence of the synthesis method (solid-state and sol-gel) and conditions of precursor processing on the ionic conductivity of the materials has been studied. Optimum conditions for the mechanical processing of precursors have been found to obtain ceramics with the highest conductivity. Li1.2Ti1.6Fe0.2Ge0.2(PO4)3 prepared by the solid-state method exhibits the highest ionic conductivity at room temperature (1.7 × 10–4 S/cm) among all samples.

Methods for the synthesis of LaNi1/3Sb5/3O6 with a rosiaite structure have been developed using citrate method and coprecipitation followed by annealing. The influence of synthesis conditions on the morphology of the samples has been demonstrated. A comparative analysis of the catalytic properties of LaNi1/3Sb5/3O6 synthesized by various methods, in the reaction of CO oxidation has been carried out. The catalyst synthesized by the citrate method demonstrated the greatest efficiency and stability (the temperature of 90% CO conversion was T90 = 336°C). The LaNi1/3Sb5/3O6 surface was studied before and after catalysis by in situ diffuse reflectance IR spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed O2 desorption. It has been shown that the catalytic oxidation of CO on the LaNi1/3Sb5/3O6 surface proceeds according to the Mars–van Krevelen mechanism and is accompanied by redox Sb3+ ↔ Sb5+ processes. It has been established that no contamination of the sample surface occurs during the catalysis process.

A new method for producing highly dispersed strontium aluminate with specified properties (low bulk density, particle size and shape) is described. The essence of the method is the sequential multi-stage heat treatment of a concentrated water-carbohydrate solution of Al(NO3)3, Sr(NO3)2, and D-glucose. The final product has a molar ratio of SrO : Al2O3 = 1 : 1. The main stages of the synthesis have been characterized by X-ray powder diffraction, SEM, and TEM methods. The initial stages of crystallization of SrAl2O4 upon heating at 1400°C have been revealed.

New iminium derivatives of the sulfonio-closo-decaborate anion have been obtained in the form of tetrabutylammonium salts (Bu4N)[2-B10H9SC(NH2)R] (R = –CH3, –CH2CH3, –CH(CH3)2, –Ph, –PhCH3), in which the iminium group acts as a protective group and allows further modification of the boron cluster anion without acting the sulfonium group. The compounds have been studied by elemental analysis, IR and 11B, 1H, 13C NMR spectroscopies. The structure of compounds (Bu4N)[2-B10H9SC(NH2)CH3] and (Bu4N)[2-B10H9SC(NH2)Ph] has been confirmed by X-ray diffraction analysis. The yield of final compounds is >80%.

The synthesis and identification of lanthanum and samarium zirconate–hafnates of the pyrochlore structure type have been reported. The heat capacity of the samples in the temperature range 310–1380 K was measured by the differential scanning calorimetry method. The temperature dependences of the cubic lattice parameters were determined, and the thermal expansion coefficients were evaluated in the range 298–1273 K using high-temperature X-ray powder diffraction. The thermal diffusivity of the samples was measured by the laser flash method, and the temperature dependences of the thermal conductivity were calculated considering the porosity of the samples.

A composition–property relationship has been developed that makes it possible to select the optimal values of the standard entropy of alkali metal borates, for which available experimental and reference data vary in wide ranges. This relationship allows one to estimate the standard entropy of unstudied alkali metal borates with sufficient validity. To ensure the reliability of the relationship, a critical analysis of the initial data borrowed from reference books and original experimental works has been carried out. Experimental measurements of low-temperature heat capacity were processed to verify the reliability of the standard entropy values of alkali metal borates presented in the literature.

The phase diagram of the SrF2–MgF2 system has been studied by differential thermal analysis (DTA) and X-ray powder diffraction (XRD). The stability area of the compound SrMgF4 is very small, and its extent is about 20°С between 870 and 890°С. The formation of compounds by magnesium fluoride and strontium fluoride with other metal fluorides is considered in the M versus X coordinates, where M is the cumulative moment of the cation and X is the cation electronegativity. Two areas of compound formation were identified for each of the fluorides. Magnesium and strontium fluorides are amphoteric compounds in terms of the Lewis acid and base theory.

Bismuth cobalt dysprosium oxide of composition Bi12.5Dy1.5CoO22.325 has been prepared by solid-state reactions. The compound has a cubic structure (space group Fm
m) with the unit cell parameter a = 0.55279(5) nm. The solution enthalpy and standard enthalpy of formation of Bi12.5Dy1.5CoO22.325 have been measured by solution calorimetry: ΔsolH0 = −1017.0 ± 7.5 kJ/mol, and ΔfH0 = −5338.8 ± 19.9 kJ/mol. The lattice enthalpy has been calculated using the Born–Haber cycle: ΔlatH0 = −99020 kJ/mol. The lattice enthalpy increases in magnitude as the lanthanide radius decreases in the neodymium–dysprosium–holmium series.

Cesium sulfatoscandate CsSc(SO4)2 (space group P
, a = b = 5.0971(1) Å, c = 8.6924(5) Å, V = 195.580(2) Å3, Z = 1) has been crystallized from aqueous solutions in layered hexagonal prisms sized up to 50 µm and up to 2–5 µm thick. Its water solubility is 0.0104 mol/L at 25 ± 1°С. A way to reduce the solubility of scandium as CsSc(SO4)2 is to increase acidity to 3.5–5.5 М H2SO4 and add Cs2SO4. Experimental evidence is supported by calculations that took into account changes in the ionic strength of the solution and the influence of the simultaneous presence of Cs+ and 
 ions. The results will be useful for those who will study the behavior of rare-metal compounds having similar properties and their separation.

The Сa(ClO3)2∙NH4Сl–H2O system has been studied in its constituent binary systems and seven inner sections, and its polythermal solubility diagram has been plotted in the range of temperatures from–42.5 to 87.5°С. The solubility diagram features the crystallization fields of ice; calcium chlorate hexahydrate, tetrahydrate, and dihydrate; and ammonium chloride. Three ternary points exist in the system. The system belongs to the complex eutonic type; its components retain their individuality and show good solubility in water. In the [40% Сa(ClO3)2 + 60% H2O]–[NH4Сl] section of the studied system, variations in crystallization temperature, viscosity, density, pH, and refractive indices of the solution have been determined. The thus-obtained results have been used to plot the composition–property diagram of the [40% Сa(ClO3)2 + 60% H2O]–[NH4Сl] section of the Сa(ClO3)2∙NH4Сl–H2O system.

Ion selective electrodes (ISEs) based on polymer plasticized membranes have been developed for the determination of benzalkonium chloride (alkyldimethylbenzylammonium), the active component being cesium bis-octodecyl-2-sulfonio-closo-decaborate Cs[B10H9S(C18H37)2] (sensor A). For the determination of norfloxacin hydrochloride, the active component is potassium tris-octodecyl-1-ammonio-closo-decaborate K[B10H9N(C18H37)3] (sensor B). It has been shown that the electrodes have a reversible potentiometric response with respect to the analyzed cations in the presence of a number of other inorganic and organic cations. The influence of the concentration of the electrode-active substance on the electrochemical characteristics of the manufactured sensor has been studied. The optimal composition of the ion-sensitive membrane has been found. It has been determined that the developed sensors provide a wide range of detectable concentrations (for sensor A, 2 × 10–7–1 × 10–2; for sensor B, 1 × 10–7–1 × 10–2) and a low detection limit (for sensor A, 1 × 10–7 M; for sensor B, 8 × 10–8 M). New ISEs can be recommended for direct potentiometric detection of free ions in water bodies and water extracts of soils.

A new method was proposed to synthesize aerogels based on Al2O3–TiO2 by the hydrolysis of mixed solutions of titanium tetrachloride and aluminum nitrate in the presence of propylene oxide, followed by supercritical drying of the obtained gels. The aerogels are characterized by a high specific surface area (140–500 m2/g) and a high specific porosity (1.7–2.7 cm3/g). Heat treatment of the Al2O3–TiO2 aerogels at temperatures up to 600°C does not lead to crystallization of titanium dioxide, whereas the formation of crystalline anatase in aerogels based on individual TiO2 is observed already at a temperature of 450°C. Using the standardized ISO 24443-2016 method, the SPF value of the obtained materials was determined, which turned out to be comparable to the characteristics of a commercial inorganic UV filter based on TiO2 (Kronos 1171). At the same time, the photocatalytic activity of the Al2O3–TiO2 aerogels turned out to be more than 120 times lower than the similar characteristics of the commercial UV filter based on titanium dioxide. The results obtained demonstrated that the Al2O3–TiO2 aerogels are promising as components of sunscreens.

The formation of hierarchically organized MoS2 films on various substrates by a hydrothermal method was studied. The influence of synthesis conditions and the substrate (a glass or a flexible carbon paper substrate) on the crystal structure of sulfide films was determined using X-ray powder diffraction (XRD). Scanning electron microscopy (SEM) showed that the films on glass substrates comprised structurally different elements, namely a continuous dense layer of spherical nanoparticles on the surface of which hierarchically organized globular agglomerates of two types are arranged. A molybdenum disulfide shell about 1.5 μm thick, consisting of hierarchically organized nanosheets less than 10 nm thick, was formed on the surface of carbon fibers that make up the carbon paper. Elemental mapping was used to evaluate the homogeneity of the MoS2 film formed on the carbon paper. Atomic force microscopy (AFM) showed that an individual carbon fiber modified with a sulfide film had a mean square roughness of about 13 nm (over an area of about 100 μm2). According to Kelvin-probe force microscopy (KPFM) data, the electron work function of the material was 4.53 eV. The electrochemical characteristics of the manufactured flexible electrode based on a hierarchically organized molybdenum disulfide film were investigated. The specific capacitance and the stability of functional and microstructural properties of the manufactured supercapacitor electrode in 2000 charge–discharge cycles were evaluated. Thus, the proposed strategy is promising for the fabrication of efficient hierarchically organized MoS2 electrodes for flexible supercapacitors.