Home – Home – Jornals – Chemistry for Sustainable Development 2020 number 1

The structure and morphology of pellets from nanoscale hydroxyapatite after CO₂ laser beam treatment are studied. It is shown that the use of a compacted layer of the material under treatment allows a significant reduction of the diameter of the laser spot. The effects of scanning speed and density of a hydroxyapatite pellet on the structure and morphology of the treated surface are investigated. It is shown that the congruent melting of the material is observed in the case of the high speed of laser beam movement. A decrease in the speed leads to the transition to sintering mode. The optimal values of the density and thickness of the sintered material are determined, which are to be kept during 3D printing of products from hydroxyapatite by means of selective laser melting.

A sequence of changes in X-ray patterns on heating of MgAl₂O₄ precursors synthesized by different methods is considered. It is shown that the presence of only spinel phase peaks can cause the erroneous conclusion of a single-phase nature of the product and thus explain its low sinterability. Mechanochemical treatment of the stoichiometric mixture of aluminum and magnesium hydroxides yields precursors, which form the powders of single-phase spinel with a crystallite size of 15-30 nm (depending on the composition of the gas medium) when heated at 1000 ^оC for an hour. Additional disaggregation of spinel powders through low-intensity mechanical treatment (10 g , 5 min) in ethanol gives rise to increased sinterability and allows attaining 95 % density at no more than 1350 ^оC, which is sufficient for successive densification by means of hot isostatic pressing. However, vacuum sintering is less efficient, leading to low density due to residual alkoxy groups enclosed in gas-tight aggregates which are formed in the course of the treatment with ethanol.

The structural and morphological characteristics of mechanochemically synthesized highly dispersed magnesium ferrite are studied. The change of structural characteristics of ultra-high molecular weight polyethylene (UHMWP) during mechanical activation is investigated. The structural characteristics of mechanochemically synthesized composite material UHMWP/magnesium ferrite, as a precursor to create materials for protection against electromagnetic radiation, are studied by means of scanning electron microscopy, X-ray diffraction and differential scanning calorimetry.

Structural changes of ultrahigh-molecular polyethylene (UHMWPE), modified by inorganic mechanocomposites Fe/M (M = TiC, HfC, TiB₂, B₄C) (70 mass %) under intense plastic deformation in a planetary ball mill, were investigated by means of X-ray phase analysis and FTIR spectroscopy. At a short treatment time, the molecular structure of initial UHMWPE is not disturbed, and the change in the shape of powder particles is due to the segmental mobility of macromolecules. The introduction of inorganic mechanocomposites (fillers) into the polymer leads to the formation of a polymer-filler interfacial zone with a branched polymer structure. The crystallinity degree of mechanochemically obtained Fe/M/UHMWPE composites is reduced to 25-40 vol. %, compared to 44 vol. % for initial UHMWPE, depending on the filler nature. No oxidative degradation of the polymer is observed under mechanical treatment.

Ceramic samples of lithium titanate spinel Li₄Ti₅O₁₂ and Li₄Ti₅O₁₂/Li₂TiO₃ composites with different content of Li₂TiO₃ as an additional phase were obtained by means of solid-phase synthesis. The phase composition and transport properties of the obtained samples are investigated. By means of impedance spectroscopy within the frequency range 20 Hz - 1 MHz, three contributions into total resistance of the samples were discovered. Assumptions concerning the reasons for higher direct-current conductivity of Li₄Ti₅O₁₂/Li₂TiO₃ composites at room temperature than that of lithium titanate spinel Li₄Ti₅O₁₂ are made.

A method is developed for the production of enterosorbent from the birch inner bark with supported biologically active betulin with improved therapeutic and prophylactic properties.

Chemical precipitation deposition of titanium oxyhydrate TiO(OH)₂ from the solutions of titanium salts and the features of thermal decomposition of TiO(OH)2 are studied for the purpose of improving and developing an efficient technology for obtaining nanodisperse powders of titanium dioxide with the required particle size and chemical composition. The effect of the basic synthesis parameters on the size of the formed agglomerates of titanium oxyhydrate is established. A method of the heterogeneous synthesis of titanium oxyhydrate using calcium hydroxide is proposed. The effect of the porosity of the crystalline precipitant (calcium hydroxide) on the disperse characteristics of the resulting product is studied. It is shown that a decrease in the average size of pores in calcium hydroxide causes a proportional decrease in the average size of the aggregated particles of titanium dioxide. Under the conditions of different methods of drying (convective, radiation and microwave), the kinetic regularities of the dehydration of titanium oxyhydrate are investigated. The effect of the temperature of titanium oxyhydrate dehydration on the size and crystalline structure of titanium dioxide powders is evaluated. To prevent agglomeration of the formed nanoparticles of titanium dioxide, it is proposed to add ammonium carbonate before the final stage of drying. Relying on the results of the studies, a technology of the synthesis of fine titanium dioxide particles with the concentration of the major component ≥98 mass % is developed.

Hydroxyapatite, fluoroapatite, and hydroxyapatite with partial substitution by fluoride and carbonate ions were obtained through mechanochemical synthesis. When a fluoride ion is introduced into the structure of hydroxyapatite, the substitution of the hydroxyl group occurs, while carbonate ion substitutes the phosphate group. Lattice parameters and the CSR of the samples were refined using the Rietveld method. It was found that the introduction of substituents into the structure of hydroxyapatite reduces the lattice parameters, which is due to the smaller size of substituting ions. The synthesized powders can be used in medicine as bioresorbable materials.

The mechanochemical method of producing supramolecular complexes of tebuconazole (TBC) was used to obtain new complex agents of plant protection from pests and diseases of cereal crops. The use of chitosan, as well as licorice root extract, in these processes made it possible to obtain preparations with improved physicochemical and biological parameters. Under field conditions, the high biological efficiency of the composition of tebuconazole with chitosan against Puccinia recondita, Septoria nodorum and Blumeria graminis was shown with a single treatment at the beginning of heading of spring wheat plants, which led to an increase in grain yield by 0.55 t/ha, while the dose of tebuconazole fungicide was reduced by a factor of 5.5. The possibility of making similar spring wheat protection products based on the combination of chitosan with licorice root extract without the inclusion of tebuconazole is demonstrated. This increases the grain productivity of wheat by 0.54-0.6 t/ha.

The reduction of silver nitrate in polyols in the presence of hydroxyethylated carboxylic acid as a stabilizer was investigated. The effect of synthesis conditions, in particular temperature, synthesis time, concentrations of silver salt, stabilizer, and sodium hydroxide, on the structural characteristics of the synthesized particles was studied by means of electron microscopy and X-ray diffraction. It was shown that large polyhedra 200-800 nm in size are formed in the system in the absence of the stabilizer, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA). In the presence of MEEAA, silver nano- and microplates with the sizes ranging from 10-20 nm to 1 µm are formed, depending on synthesis conditions. The optimal reaction conditions were determined for obtaining silver plates 100-500 nm in size, with the dominating 200-300 nm fraction: temperature, 100 °C; synthesis time, 1 h; MEEAA to Ag molar ratio, 3 : 1. The type of polyol was shown to affect both the morphology of the resulting particles and the fraction of plates and polyhedra in the final product. Thus, the fraction of polyhedra with respect to the plates increases when passing from ethylene glycol to triethylene glycol and propylene glycol. The effect of the alkaline reagent (NaOH) on the composition, size, and morphology of reduction products was studied. It was shown that the rate of silver ion reduction increases significantly in the presence of NaOH, which allows carrying out the process at room temperature. At a molar ratio of NaOH to Ag equal to 4 : 1, nanoplates 10-20 nm in size are formed. As-synthesized silver micro- and nanoplates can be used in the development of conductive materials, including pastes and inks for printed electronics.

A solid-phase method was developed for the synthesis of β-tricalciumphosphate (β-TCP) with the stoichiometric composition and with partial substitution of calcium ions for copper, zinc and silver ions. The method involves preliminary preparation of precursors by means of mechanical activation of reaction mixtures. The start of β-TCP formation was detected directly during the activation of reaction mixtures in the mill. The optimal conditions for activation, the temperature and the duration of annealing were determined.

The anatase phase of titanium dioxide TiO₂ is metastable and irreversibly converts to rutile at a temperature above 700 °C. This is accompanied by a significant decrease in the specific surface area and a change in the porous structure. Modification of titanium dioxide by the addition of alumina leads to the formation of the nanocrystalline structure of anatase and to a significant increase in the temperature of anatase to rutile phase transition up to 950 °C. After high-temperature annealing, the Al₂O₃-TiO₂ sample is characterized by a higher specific surface area and a better developed porous structure than those of pure anatase with the regular crystal structure. The high thermal stability of the anatase phase in supported Pt/(Al₂O₃-TiO₂) catalysts under calcination provides a high dispersion of platinum particles, which leads to the rather high catalytic activity of these catalysts in CO oxidation.

The use of copper oxide complexes (CC) of various structures: CC-I (copper tetrammine complex with the ground state of copper ions (d_x² - d_y²), characterized by a weak exchange magnetic interaction in the EPR spectra) and CC-III (Cu²⁺ ions with the ground state (d_x² - d_y²), with the strong exchange magnetic interaction) in the synthesis of Cu/ZSM-5 catalysts allowed us to study the effect of their structure on the physicochemical and catalytic properties in the decomposition of nitrogen (I) oxide (N₂O). It was demonstrated by means of H₂-TPR and IR spectroscopy of adsorbed CO that the nature of the reduction of Cu/ZSM-5 catalysts is determined by the state of copper in the catalyst. It was established that the highest catalytic activity is observed for the catalysts prepared using CC-III. Extraframework CuO-like clusters stabilized on the outer surface of zeolite crystallites prepared using CC-III are the most effective centres for the decomposition of nitrous oxide, and the activity of catalysts increases with an increase in copper content.

Processing of the nitric solutions from the production of bismuth compounds by adding water was studied by means of X-ray phase and chemical analyses, and electron microscopy. It is shown that bismuth gets precipitated from solutions at the process temperature of 65±5 °C and pH 0.7-1.0 in the form of oxohydroxonitrate [Bi₆O₄(OH)₄](NO₃)₆•H₂O, and washing with water causes hydrolysis with the formation of high-purity [Bi₆O₅(OH)₃](NO₃)₅•3H₂O compound. These compounds are used as precursors for obtaining high-purity bismuth compounds through a solid-liquid reaction. It is demonstrated that the treatment of bismuth oxohydroxonitrate with the solutions of citric, gallic, tartaric, salicylic, nitric acids and ammonium carbonate may result in obtaining bismuth citrate BiС₆Н₅О₇, bismuth oxogallate trihydrate C₆H₂(OH)₃COOBiO•3H₂O, bismuth ditartrate trihydrate [Bi(C₄H₄O₆)(C₄H₅O₆)]•3H₂O, bismuth oxide salicylate Bi(C₇H₅O₃)O, bismuth nitrate pentahydrate Bi(NO₃)₃•5H₂O, bismuth oxocarbonate (BiO)₂CO₃, respectively. The powders of metal bismuth with particle size 1-5 and 10-50 mm were obtained by the reduction of oxohydroxonitrates of the compositions [Bi₆O₄(OH)₄](NO₃)₆•H₂O and [Bi₆O₅(OH)₃](NO₃)₅•3H₂O, respectively, in the solution of benzyl alcohol. The reduction of these oxohydroxonitrates in ethylene glycol solution in the presence of hydrazine hydrate in the case of [Bi₆O₄(OH)4](NO₃)₆•H₂O results in the formation of bismuth glycolate, while in the case of [Bi₆O₅(OH)₃](NO₃)₅•3H₂O - in the formation of metal bismuth with particle size 10-50 mm. The powders of metal bismuth with particle size 1-5 and 10-50 mm were obtained by means of the reduction of the compounds [Bi₆O₄(OH)₄](NO₃)₆•H₂O and [Bi₆O₅(OH)₃](NO₃)5•3H₂O, respectively, in the aqueous medium with sodium borohydride as the reducing agent, with the molar ratio of bismuth/sodium borohydride = 1, pH 12 and a temperature of 25 °C.