Vol 99, No 10 (2025)

Solid solutions K_2–2x Na_2x Fe_1.5Nb_0.5(PO₄)₃ (0 ≤ x ≤ 1) are studied to determine the stability ranges of the NASICON and langbeinite structural types and to evaluate the mixing energetics. The materials under investigation may be used as cathodes for Na-ion batteries. Powder samples were obtained by a solid-state method and characterized by X-ray microanalysis, X-ray diffraction, and differential scanning calorimetry. Structural refinement was carried out by the Rietveld method using powder X-ray diffraction data at room temperature. It was established that phases isostructural to the mineral langbeinite (K₂Mg₂(SO₄)₃, space group P2₁3) crystallize in the range 0 ≤ x ≤ 0.4, while phases isostructural to NASICON NaZr₂(PO₄)₃ (space group R3-c) crystallize in the range 0.9 ≤ x ≤ 1. Standard enthalpies of formation were determined by high-temperature molten-salt calorimetry in a sodium molybdate melt (3Na₂O·4MoO₃) at 800°C using a Tian–Calvet-type isoperibolic differential calorimeter. The trends in the obtained energetic characteristics are discussed in relation to the structural evolutions across the indicated composition range of the solid solutions. This study expands current knowledge on the isomorphism of alkali cations in framework structures demonstrating possible pathways for changing properties within the investigated series.

The stability constants of cadmium(II) complexes with the glycylglycinate anion in aqueous dimethyl sulfoxide (DMSO) solutions were determined by potentiometric titration at 298 K and an ionic strength of 0.1 M. An increase in DMSO concentration in the solution leads to higher stability of cadmium(II) glycylglycinate complexes. Using both experimental and literature data, the Gibbs transfer energies of cadmium(II) glycylglycinate complexes from water to aqueous–DMSO solvent mixtures were calculated, and the contribution of reagent resolution to the change in Gibbs energy of the complex formation reaction was analyzed. It was shown that the enhanced stability of cadmium(II) glycylglycinate complexes in aqueous DMSO solutions is mainly due to weakened solvation of the ligand.

The interactions of the polar basic amino acid L-lysine (Lys) with structural isomers of pyridine monocarboxylic acid: picolinic (PA), nicotinic (NA) and isonicotinic (INA) acids in an aqueous solution were studied by solution calorimetry at 298.15 K. The experimental data allowed us to establish the formation of Lys complexes with the indicated isomers with a stoichiometry of 1:1. The thermodynamic parameters were determined: binding constants, enthalpies of complex formation, Gibbs energies and entropies. The stability of the formed complexes depends on the structural isomerism of pyridine carboxylic acid and increases in the series: PA < NA < INA. It was shown that the main contribution to the stabilization of the formed complexes is made by the enthalpic component of the Gibbs free energy of complex formation.

The chemical composition of the medical enterosorbent Polisorb MP (colloidal silica particles) and its surrounding dispersive medium was determined using AES ICP, CHNS analysis, TGA, and capillary electrophoresis. Dispersions of Polisorb in water and in 40% and 95% aqueous-ethanol solutions were prepared and characterized by photon correlation spectroscopy (PCS) and phase analysis light scattering (PALS). The number-average hydrodynamic diameter of fractal-like aggregates of primary particles was 105 – 135 nm, and the electrophoretic potential ranged from –28 to –22 mV. The charge of a single aggregate decreased with increasing alcohol content in the sequence: –89, –54, and –29 e. The maximum sorption of methylene blue sharply decreased from 10 to 0.7 mg/g under these conditions. It was shown that the maximum sorption values significantly exceed the number of negative surface centers calculated by PALS within the spherical aggregate model, but are lower than the number of silanol groups determined by TGA. A cation-exchange mechanism for the sorption of cationic dyes by Polisorb MP is hypothesized.

The thermal stability of acrylic stones was studied in the temperature range of 250- 650 K. It was found that an excessive presence of mineral pigments and fillers in the formulation of certain samples facilitates the thermal decomposition of the organic components of the polymer stones, negatively affecting their thermal stability.

Mechanoactivation has a significant effect on the properties of phosphogypsum (PG) and on the efficiency of rare earth element (REE) extraction from it. When the process is conducted in "wet" mode using bead-type activators, the phosphogypsum samples retain their crystallinity. The increase in REE leaching from activated phosphogypsum is associated with an increase in various structural defects in its crystal lattice, the cumulative effect of which is expressed as microstrains caused by first- and third-order stresses. Kinetic studies of lanthanide leaching from activated samples showed that the process rate is limited by their internal diffusion. The calculated amount of energy absorbed by the PG sample after mechanoactivation was 6.61 kJ/mol.