Vol 68, No 11 (2023)

The sorption properties of amorphous cerium(IV) hydrogen phosphate and crystalline phases NH4Ce2(PO4)3, (NH4)2Ce(PO4)2·H2O, and Ce(OH)PO4 towards the 243Am(III), 232Th(IV), 237Np(V), and 233, 238U(VI) radionuclides were studied in aqueous media at pH 1, 4, 7, and 10 for 24 h. The highest degree of sorption (up to 100%) was found for amorphous cerium(IV) hydrogen phosphate. The pH dependences of radionuclide sorption for crystalline compounds were shown to be similar to one another: the highest sorption was observed at pH 7 (up to 100% for 243Am(III)), while the lowest values were observed for pH 10 and 1. An exception was provided by 237Np(V), the sorption of which was close to zero in the pH range of 1–7 and reached 60% at pH 10. Keeping amorphous and crystalline cerium(IV) phosphates in acid medium leads to quantitative desorption of all of the tested radionuclides within the first 5 h.

Interaction of rare-earth oxides (Pr, Tb, Er) with periodic acid or sodium iodate under hydrothermal conditions in the presence of Na2HPO4⋅12H2O leads to formation of complex NaLn(IO3)4 iodates. The compounds of Pr and Tb are reported for the first time. Single-crystal studies reveal that they are isostructural to the previously reported analogs of other rare-earths and adopt the non-centrosymmetric space group Сс. Polycrystalline samples generate a strong SHG signal above that of the potassium dihydrogen phosphate reference standard. They also exhibit wide optical transparency areas and high thermal stability.

Calcium silicates with nanosized needle-like structure have been obtained from phosphorite by hydrothermal synthesis. Phosphorus is recovered from phosphorite as sodium phosphate solution under conditions of autoclave treatment of phosphorite with alkaline solution in the presence of silicon dioxide at 250°C. This approach enables involvement of low-phosphorus raw materials into non-waste processing owing to the synthesis of calcium silicates suitable in many branches of industry. Thus prepared phosphate solutions are applicable in agriculture and, after appropriate purification, in food industry. Hydrothermal synthesis conditions have been determined: temperature of 250–300°C, leaching time of 3 h, and NaOH concentration of 150 kg/m3.

A wide variety of oxidation states and coordination numbers of complexing cations, various redox properties, high stability of the coordination center, as well as a unique electronic structure determine the catalytic activity of porphyrin complexes of noble metals in various reactions with organic substrates. This review presents the types of catalytic reactions involving compounds of ruthenium, rhodium, iridium, palladium, platinum, and gold with porphyrins, with an emphasis on the features of intermediates depending on the nature of the metal, electronic and steric effects of peripheral substituents of the macrocycle. The presented data provide a theoretical basis that can contribute to the development of innovative materials for catalysis based on metalloporphyrins, as well as the creation of new homogeneous and heterogeneous catalysts.

A technique for constructing force fields based on the use of genetic algorithms is proposed, which is aimed at parameterization of potentials intended for computer simulation of polyatomic nanosystems. To illustrate the proposed approach, a force field has been developed for modeling layered modifications of WS2, including multi-walled nanotubes, the dimensions of which are beyond the capabilities of ab initio methods. When determining the potential parameters, layered polytypes of bulk crystals, monolayers, bilayers, and nanotubes of small diameters were used as calibration systems. The parameterization found was successfully tested on double-walled nanotubes, the structure of which was determined using density functional calculations. The obtained force field was used for the first time to model the structure and stability of achiral multi-walled nanotubes based on WS2. The interwall distances obtained from the simulation are in good agreement with the results of recent measurements of these parameters for existing nanotubes.

Isobaric heat capacity measurements in the range 2.4–1807 K have been performed by relaxation calorimetry, adiabatic calorimetry, and differential scanning calorimetry on a Ho2O3‧2HfO2 solid solution sample prepared and characterized by X-ray powder diffraction, electron microscopy, and chemical analysis, and thermodynamic functions have been calculated. The Schottky anomaly contribution has been determined in the range 2.4–300 K.

Phase equilibria in the Cu2Se–Cu8SiSe6–Cu8GeSe6 area of the Cu2Se–SiSe2–GeSe2 system have been studied using differential thermal analysis (DTA), X-ray powder diffraction analysis (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDX). The results served to plot a Т–х diagram of the Cu8SiSe6–Cu8GeSe6 boundary system, a series of polythermal sections, and a 300-K isothermal section of the phase diagram and a liquidus surface projection for the title system. The primary crystallization and homogeneity fields of phases, and the characters and temperatures of invariant and monovariant equilibria have been determined. In the Cu8SiSe6–Cu8GeSe6 boundary system, continuous solid solutions have been found to exist between the high-temperature phases of the terminal compounds and extensive homogeneity area based on their low-temperature phases were found. The crystal lattice types and unit cell parameters have been determined for the terminal compounds and both phases of solid solutions using X-ray powder diffraction data. The prepared phases of variable composition are of interest as environmentally friendly functional materials.

Synthesis methods, thermodynamic and functional properties of compounds based on bismuth niobates doped with rare-earth elements (REEs) are presented. These compounds are promising materials for fuel cells, ceramic oxygen generators, electrocatalysis, etc. As show the data generalized, most compounds have a cubic structure of the δ-form of bismuth oxide, which has the highest ionic conductivity among solid-state ionic conductors. The compounds have high lattice enthalpy and are therefore promising high-energy compounds. The review summarizes studies on the basic thermodynamic characteristics of bismuth niobates doped with rare earth elements. The change in standard enthalpies of formation, lattice enthalpies, and heat capacity when replacing one rare earth element with another is analyzed. It is shown that as the radius of rare earth elements decreases, the standard enthalpies of formation increases and lattice enthalpies increases. The change in ionic conductivity with changes in temperature and rare earth element content has been studied. It has been shown that with increasing temperature and REE content, conductivity increases.

Effect of structure of phosphorylketones containing flexible alkyl and conformationally rigid fragments in the linker on extraction ability toward actinides and lanthanides has been studied. It has been shown that the introduction of conformationally rigid cycloalkanediyl and alkenediyl fragments in the bridge between P=O and C=O groups in the structure of molecule decreases efficiency of extractants for both actinides and lanthanides. At the same time, the introduction of flexible alkyl groups in linker structure increases complexing and extraction ability. This dependence has been explained theoretically by modeling complexation (DFT, PBE, cc-pVDZ), monodentate coordination was observed for all studied phosphorylalkanones

Ceramic-forming zirconium (hafnium)-containing yttriumoxane alumoxanes, precursors of multicomponent ceramics based on alumina, yttria and zirconia/hafnia, were synthesized by co-condensation of chelated alkoxyalumoxanes, yttrium acetylacetonate hydrate (or organic yttriumoxane alumoxanes) and zirconium or hafnium acetylacetonate. The physicochemical properties of zirconium (hafnium)-containing yttriumoxane alumoxanes were studied. Computational models of the group and elemental composition of oligomeric Zr(Hf)-containing yttriumoxane alumoxane molecules were proposed. According to X-ray diffraction and scanning electron microscopy data, pyrolysis of the oligomers at 1500–1600°C results in multicomponent nano- or fine-crystalline ceramic powders, depending on the Al/Y and Al/Zr(Hf) molar ratios.