Vol 64, No 7 (2019)

Composites based on electrochemically active components, LiFePO₄, LiMn₂O₄ and LiNi_0.82Co_0.18O₂, for the use as cathode materials for lithium-ion batteries were synthesized using ultrasonic treatment. The effects of the sonication mode (series LiFePO₄–LiMn₂O₄) and component ratio (series LiFePO₄–LiNi_0.82Co_0.18O₂) on the electrochemical performance of the resulting composites were studied. The obtained composites were examined by scanning electron microscopy and powder X-ray diffraction and tested in coin-type cells with lithium anode. Positive electrodes based on the obtained composites showed enhanced electrochemical performance.

We present the results of characterization of prepared composites comprising dicalcium phosphate dihydrate (DCPD, brushite) and hydroxyapatite in the polymeric matrix of chitin and chitosan. The crystallite sizes increase as the chitosan and chitin percentage in the composite increases. When samples are dissolved in isotonic saline, the degradation rate of brushite composites decreases as the chitosan and chitin percentage in the sample increases; for hydroxyapatite composites, an opposite trend is typical. The samples are shown to change their weight as a result of heat treatment.

Pd/TiO₂–SiO₂ xerogels containing 0.15–0.75 wt % palladium are prepared from Pd(NO₃)₂ · 2H₂O solutions in a mixture of tetrabutoxytitanium (TBT) and tetraethoxysilane (TEOS) in a desiccator under acetic acid–water vapors in the batch mode at 20°С followed by drying and calcination of the material at 850°С. IR spectroscopy showed that the presence of Pd(NO₃)₂ · 2H₂O has no effect on the amount of newly formed Ti–O–Si bonds in the double oxide TiO₂–SiO₂ over the range of salt concentrations studied. X-ray powder diffraction showed that palladium present in the xerogel calcined at 850°С is in the form of Pd(0) nanoparticles. The electron-microscopic morphology study showed that the items prepared (Pd(0) nanoparticles) had near-spherical shapes; their sizes fell in the range 20–230 nm. A means for varying Pd(0) nanoparticle size in the material is to vary the palladium(II) salt concentration at the dissolution stage.

The crystal-chemical analysis of compounds with a structure containing AlC_n coordination polyhedra has been performed using the intersecting sectors method and Voronoi–Dirichlet polyhedra (VDPs). It has been found that the aluminum atoms in the carbon environment have coordination numbers (CNs) 1–7 and 10, with the most typical CN of the aluminum atom being 4. There is a common linear dependence of solid angles of VDP faces corresponding to covalent and noncovalent Al–C contacts on the corresponding internuclear distances. It has been demonstrated that the length of Al–C bonds varies in the range 1.90–2.77 Å, while the VDP volume of the aluminum atom is roughly independent of its CN, being 11.4(7) ų. Criteria for evaluation of the existence of the Al–Al cluster bond in the structure of organoaluminum compounds have been suggested, and the agostic Al⋅⋅⋅H–C interactions have been examined.

Germanate Tb₂Ge₂O₇ has been prepared by solid-phase synthesis from a stoichiometric mixture of Tb₂O₃ and GeO₂ by sequential firing in air at temperatures of 1273–1473 K. The effect of temperature on its molar heat capacity has been studied by differential scanning calorimetry. According to the obtained dependence C_p = f(T), the thermodynamic properties (enthalpy and entropy changes and the reduced Gibbs energy) have been calculated, and the specific heat value at 298 K has been estimated.

The ternary system Nd₂S₃–Ga₂S₃–EuS was studied by physicochemical analysis methods. The projection of the liquidus surface was constructed, and the boundaries of the glass formation region were found. It was determined that the ternary system consists of ten fields of primary crystallization of individual phases and the glass formation region. The thermolysis of the synthesized glasses was investigated, and their IR spectra were recorded. In the course of the thermolysis in an inert atmosphere, the glass (Ga₂S₃)_0.70(Nd₂S₃)_0.25(EuS)_0.05 softens at 1010 K and then crystallizes at 1110 K. The mass loss proves that the exothermic events observed in the temperature range 1145–1225 K are related to stage-by-stage glass decomposition.

The quaternary reciprocal system Na,Rb||F,I,CrO₄ was studied, low-melting mixtures based on which are promising as fusible electrolytes for chemical current sources, heat-storage materials, and media for growing single crystals. The system was partitioned into simplexes using graph theory, and the tree of phases of the system was constructed. The tree of phases is linear and contains four stable tetrahedra sharing stable cutting triangles. The combined stable tetrahedron NaF–RbI–RbF–Rb₂CrO₄ was investigated by differential thermal analysis. The crystallization surface of this stable tetrahedron is represented by the volumes of sodium fluoride, rubidium iodide, rubidium fluoride, rubidium chromate, and the compound Rb₃CrO₄F. Monovariant equilibrium lines meet at two quaternary invariant points: eutectic E^◻491 and peritectic P^◻508.

In order to study the effects of inorganic and organic modification on the adsorption properties of red soil (RS), ferric chloride (FC) and hexadecyl trimethyl ammonium bromide (HTAB) surface-modified red soil have been prepared and characterized by SEM, FT-IR and X-ray diffraction. Adsorption properties of Th(IV) on natural red soil (NRS), FC surface-modified red soil (FC-RS), and HTAB surface-modified red soil (HTAB-RS) have been investigated by batch technique. The inorganic and organic modification have been found to greatly improve the adsorption kinetics and thermodynamic properties and increase the adsorption capacity as compared with NRS. The adsorption of Th(IV) on the three adsorbents have been strongly dependent on pH and ionic strength, and intra-particle diffusion was the rate-controlling step. The non-linear pseudo-second-order kinetic model could fit the kinetics much better compared with the linear forms, and the linear and non-linear Langmuir expressions could fit the thermodynamics. The results obtained denote on successful application of inorganic and organic modification to treatment of water samples spiked to Th(IV) ions.

With taking into account the β-factor value of the lithium ion aqua complex found earlier, the single stage extraction coefficient of isotope separation (α) of the ⁶Li–⁷Li pair has been calculated for the extraction system containing the benzo-15-crown-5–Li⁺ (H₂O)Cl^– complex in the organic phase, which corresponds to a real extraction process. Similar calculations have been carried out for other anions, as well as for various benzo-15-crown-5 derivatives with varying the number and type of donor atoms and different substituents in the benzene ring. Quantum-chemical calculations of the vibrational frequencies of the isotopic forms of the crown ether complex were performed using the Firefly program with the RHF/6-311++G** basis set. It has been shown that the isotope separation factor in this case is lower than in the case of the anhydrous benzo-15-crown-5–Li⁺Cl^– complex and the model benzo-15-crown-5–Li⁺ (H₂O) complex.

The potential of the Y₂O₃–ZrO₂–HfO₂ system for synthesizing the casting mold ceramic of the composition 15 mol % Y₂O₃ : 60 mol % ZrO₂ : 25 mol % HfO₂ was investigated. The effect of technological parameters on the morphology and main properties of ceramic molds produced by investment casting using the ceramic of the above composition was studied, and the basic recommendations for the further development of their production technology were considered. It was determined that a high-refractory casting mold stable to 2773 K can be obtained by conventional investment casting, in which the solid-phase sintering of the ceramic does not rule out the simultaneous combination with the synthesis of the chosen ternary solid solution of the composition 15 mol % Y₂O₃ : 60 mol % ZrO₂ : 25 mol % HfO₂, acting as a high-temperature binder.

Composite ferrite nanoparticles Co_1 – xZn_xFe₂O₄/Ni_1 – xZn_xFe₂O₄, x = 0.1–0.5) have been synthesized by co-precipitation method and annealed at temperature of 800°C for 2 h in air. The synthesized samples have been characterized by X-ray powder diffraction, FE-SEM/EDS, and UV-Vis spectroscopy. The prepared nanoparticles exhibit a cubic crystal structure observed from X-ray powder diffraction experiment. It has been observed that the Co_0.7Zn_0.3Fe₂O₄/Ni_0.7Zn_0.3Fe₂O₄ nanoparticles exhibit higher optical absorbance spectrum at 400 to 800 nm wavelength due to its smaller crystal size (100.8 nm) as compared to the composite ferrite nanoparticles Co_0.9Zn_0.1Fe₂O₄/Ni_0.9Zn_0.1Fe₂O₄ (176.2 nm), Co_0.8Zn_0.2Fe₂O₄/Ni_0.8Zn_0.2Fe₂O₄ (134.3 nm), Co_0.6Zn_0.4Fe₂O₄/Ni_0.6Zn_0.4Fe₂O₄ (165.6 nm), and Co_0.5Zn_0.5Fe₂O₄/Ni_0.5Zn_0.5Fe₂O₄ (245.6 nm) nanoparticles. The photocatalytic activity of composite ferrite nanoparticles have been studied by performing the decomposition of methylene blue dye solution under UV light irradiation within 0 to 4 h. The methylene blue dye solution was considerably photodegraded by Co_0.7Zn_0.3Fe₂O₄/Ni_0.7Zn_0.3Fe₂O₄ photocatalyst under UV irradiation within 0–4 h to the efficiency of 96%. The pseudo first order rate constant of the degradation has been found to be 0.0144 S^–1. The degradation mechanisms are discussed.