Volume 68, Nº 3 (2023)

Cesium-containing compounds of hydrated vanadium(V) oxide of general formula СsxV2O5·nH2O, where 0.1 ≤ x ≤ 0.6 and 0.8 ≤ n ≤ 1.2, were prepared by hydrothermal, hydrolytic, and sol–gel processes. The preparation conditions were found to determine the intercalated cation (Cs+) homogeneity range and the vanadium(IV) percentage in the samples. The prepared compounds were characterized by a set of physicochemical methods, namely, IR spectroscopy, X-ray powder diffraction, thermogravimetric analysis, scanning electron microscopy, and low-temperature nitrogen adsorption. The СsxV2O5·nH2O compounds prepared by the hydrolytic and hydrothermal methods had the highest specific surface area, equal to 34.0 and 16.5 m2/g, respectively. The temperature-dependent electrical conductivities of СsxV2O5·nH2O samples were measured to estimate the activation energy of conduction in compounds having various vanadium(IV) percentages. It is only in the high-temperature range that the activation energy of conduction depended on the V4+ percentage in the sample; the least value was found in the hydrothermally prepared Сs0.6V2O5·H2O samples.

The possibility of preparation of crystalline double cerium(IV) phosphates (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3 under the conditions of microwave-assisted hydrothermal synthesis has been analyzed. It has been shown that these phosphates in a single-phase state can be obtained in the temperature range of 130–190°С with a synthesis duration of ≥5 min, while the phase composition of the synthesis products is determined by the molar ratio of ammonia and phosphoric acid in the reaction mixture. Short-term (5 min) low-temperature (130°С) hydrothermal synthesis under microwave heating leads to the preparation of (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3 with a particle size of ~70 and ~200 nm, respectively. At higher temperatures and treatment times (190°C and 24 h), the particle size of these phases increases to ~200 and ~500 nm, respectively. For the first time, the value of the optical band gap for (NH4)2Ce(PO4)2⋅H2O was determined to be 2.8 and 3.1 eV for indirect and direct transitions, respectively.

New values for the standard enthalpies of formation of titanium fluorides at 0 K have been obtained by revisiting data on homogeneous and heterogeneous equilibria with their participation (kJ/mol): –1403.2 ± 2.7 for TiF3(c), –1144.2 ± 3.3 for TiF3, –2349.4 ± 6.3 for Ti2F5(c); –933.7 ± 6.8 for TiF2(c), and –650.4 ± 2.4 TiF2. The thermodynamic metastability of TiF2(c) has been shown.

Complex formation of aqua palladium(II) ions with glycine (Gly), β‑alanine (β-Ala), and taurine (Tau) in aqueous solution was studied by spectrophotometric titration at I = 1.0 mol/L (HClO4 + NaClO4) and T = 25 ± 1°C. A monoligand complex appeared at pH 0 in the H‒Pd–Gly system under the conditions of our experiment; mono- and biscomplexes were formed at pH 1. In the H‒Pd‒β-Ala system, a monoligand complex was formed at pH 1 and mono- and biscomplexes were formed at pH 2. In the H‒Pd‒Tau system, a monoligand complex was formed at pH 1 and 2. Molar absorption coefficients were calculated: the peak absorption occurs at λ = 370 nm and ε = 203 L/(mol cm) for the monoligand glycinate complex [PdGly(H2O)2]+; at λ = 325 nm and ε = 274 L/(mol cm) for the biscomplex [PdGly2]0; at λ = 365 nm and ε = 342 and 297 L/(mol cm) for the β‑alaninate [Pdβ‑Ala(H2O)2]+ and taurinate [PdTau(H2O)2]+ monoligand complexes, respectively; and at λ = 330 nm and ε = 549 L/(mol cm) for the β‑alaninate biscomplex [Pdβ‑Ala2]0. Logarithmic concentration formation constants were calculated for glycinate (log β1 = 15.03 ± 0.07, and log β2 = 28.97 ± 0.28), β-alaninate (log β1 = 13.94 ± 0.05, and log β2 = 25.24 ± 0.06), and taurinate (log β1 = 9.74 ± 0.08) palladium(II) complexes.

The formation of mixed-ligand complexes of various compositions in the Zn–L-histidine (His)–L-ornithine (Orn) system has been studied by pH-metry, calorimetry, and NMR spectroscopy. The thermodynamic parameters (log K, ΔrG0 ΔrH, ΔrS) of the reactions of their formation at 298.15 K and ionic strength I = 0.5 (KNO3) have been calculated. Based on the comparative analysis of thermodynamic parameters, the most probable method for the coordination of amino acid residues in mixed complexes has been proposed.

Tetragermanates Ba2Gd2 – xSmxGe4O13 (x = 0.025–0.8) have been synthesized by the solid-phase method. Solid solutions crystallize in the monoclinic crystal system (space group С2/с, Z = 4) and are members of a small family of inorganic compounds containing [Ge4O13]10– anions. The photoluminescence properties of germanates upon excitation by radiation with λex = 275 nm have been studied. The spectra of the compounds show a broad band with a maximum at 313 nm and a set of lines in the range of 525–730 nm, corresponding to intraconfigurational 4f–4f transitions in Gd3+ and Sm3+ ions. It has been found that germanate Ba2Gd1.95Sm0.05Ge4O13 has the maximum luminescence intensity. For this sample, the color characteristics and the temperature dependences of the intensity ratios of the main luminescence bands upon heating to 498 K have been studied. It has been concluded that Ba2Gd1.95Sm0.05Ge4O13 can be used as a material for non-contact temperature sensing and light emitting diodes.

The development of new materials with antibacterial properties is a promising direction in the field of nanotechnology. In this work, ZnO–Ag nanoparticles with a silver content of 0.1–50 at % have been fabricated by the exploding wire method. ZnO–Ag nanoparticles absorb visible light and destroy the model dye Rhodamine B. The introduction of silver into nanoparticles has made it possible to shift the main absorption edge to 1.59–2.74 eV. The determined optimal content of silver in nanoparticles of 12 at % has ensured the degree of Rhodamine B decoloration by 85% within 60 min of exposure to visible light and has completely stopped the growth of E. coli bacteria at a concentration of 15.6 µg/mL. In addition, nanoparticles containing 12 at % silver have sterilized a sample of natural water contaminated with microorganisms. The results obtained offer an efficient method for the synthesis of antibacterial nanocomposites with heterojunctions employing a high-performance technique for producing nanoparticles, namely, the exploding wire method.

Arrays of titanium dioxide (TiO2) nanotubes with different chemical compositions have been synthesized; their structural properties have been studied, and the characteristics of spin centers (defects) have been determined. All samples have appeared to contain carbon. It has been established that the main type of spin centers in TiO2 nanotubes are dangling carbon bonds, and their concentration correlates with the carbon content in the obtained structures. Under illumination, a reversible increase in the concentration of defects occurs, which is caused by their photoinduced recharging in the process of impurity absorption. This process is accompanied by an increase in the concentration of photoexcited electrons in the conduction band. The originality and novelty of the work are determined by the development of a method for controlling the density of defects and, accordingly, the concentration of photoinduced electrons by thermal treatment of samples under various conditions. The results open up new possibilities for the development of photocatalysts based on titanium dioxide nanotubes with a controlled electron concentration in the conduction band that function in the visible range of the spectrum.