Исследовано взаимодействие водного раствора нитрата стронция с допированными магнием калий-титанатными нанотрубками, синтезированными методом соосаждения с последующей гидротермальной обработкой. Установлено, что после 2 ч выдержки в растворе при комнатной температуре наибольшую сорбционную емкость проявил состав с замещением 10 ат.% титана магнием. Полученные результаты показывают перспективность использования допированных магнием калий-титанатных нанотрубок в качестве адсорбентов ионов стронция из водных растворов.

The interaction of an aqueous solution of strontium nitrate with magnesium-doped potassium titanate nanotubes synthesized by coprecipitation followed by hydrothermal treatment is studied. It is found that after 2 h of exposure in the solution at room temperature, the composition with the replacement of 10 at % titanium by magnesium showed the greatest sorption capacity. The results obtained show the promise of using magnesium-doped potassium titanate nanotubes as adsorbents of strontium ions from aqueous solutions.

Hollandite-based ceramics are mainly produced by the traditional solid-phase method. However, the use of "wet" chemistry can improve its morphological characteristics, increase porosity, etc., as well as change the electrophysical properties. In this study complex oxides with hollandite-type structure in the system K2O-MeO-TiO2 (Me = Mg, Ni, Cu) were synthesized by combustion of citrate-nitrate compositions (a special case of the sol-gel method). The structure of obtained material was studied using the XRD and SEM analysis. While studying the electrophysical properties, it was found that in a stream of hydrogen, the electrical conductivity of hollandites with magnesium and nickel increases significantly (by 2-3 orders of magnitude) over the entire studied temperature range. Thus, ceramics based on these hollandites can be used to create hydrogen sensors.

Ceramics based on hollandites are known to mainly produced by the conventional solid-phase method. However, the use of various sol–gel methods in some cases makes it possible to change the temperature and time its synthesis, morphological characteristics, porosity, and electrophysical properties. In this work, ceramic materials based on a number of cesium titanate hollandite phases were synthesized by combustion of citrate–nitrate mixtures. The structure of the obtained materials was studied by X-ray powder diffraction analysis and scanning electron microscopy. Investigation of the electrophysical properties showed that, in a hydrogen flow, the electrical conductivity of hollandites with aluminum and nickel increases significantly (by 2.5–3 orders of magnitude) throughout the studied temperature range. Thus, ceramics based on these hollandites can be considered promising for creating hydrogen sensors and fuel cells.

Materials of the hollandite structure in the K2O–MeO(Mе2O3)–TiO2 (Ме = Al, Ni, Mg) system, synthesized by two methods (solid-phase synthesis and pyrolysis of citrate–nitrate compositions), were studied. The pyrolysis, compared to the traditional solid-phase synthesis, yielded the materials with the more developed specific surface and, as a consequence, enhanced performance in sorption of a model dye, Methylene Blue (for K2MgTi7O16, q = 18.75 mg g–1). The K2Al2Ti6O16 sample, also prepared by pyrolysis, showed the highest catalytic performance in oxidation of СО and Н2. The hydrogen oxidation on this catalyst occurred to 95% at 355°С with the performance of ~0.21 × 10–5 mol g–1 s–1, which is two times higher compared to the sample of the same composition prepared by the solid-phase method. The hollandites show promise as sorbents and catalysts for gas treatment.

The results of the study of novel composite solid electrolytes based on the CаO–Bi 2 O 3 –Fe 2 O 3 system are presented. These materials have a mixed electronic-ionic conductivity which increases with the growth of the Fe 2 O 3 content. In the (СаO) 0.26 (Bi 2 O 3 ) 0.74 –Fe 2 O 3 section, a part of the oxygen-ionic component increases with an increase in the Fe 2 O 3 content and, in contrast, the oxygen conductivity decreases in the (СаO) 0.2 (Bi 2 O 3 ) 0.8 –BiFeO 3 section. These materials are interesting in terms of their use as elements of electrochemical devices, for example, in solid oxide fuel cells, electrolyzers for obtaining extra pure gases (oxygen, hydrogen), and electrochemical oxygen sensors.

Nanosized La 1– x Dy x PO 4 · n H 2 O powders are synthesized by the sol-gel method using direct and reverse precipitation. The formation of a continuous series of hexagonal solid solutions based on LaPO 4 · n H 2 O is confirmed by the XRD and DSC/TG methods. A continuous series of monoclinic solid solutions based on LaPO4 is formed at temperatures higher than 600°C. A reflex corresponding to a tetragonal form of DyPO 4 is formed during the calcination of DyPO 4 powder at 850°C. Two types of solid solutions are observed at temperatures of 1000–1200°C, namely, monoclinic solutions based on LaPO 4 (to x ≈ 0.7) and tetragonal solutions based on DyPO 4 (0.90 ≤ x ≤ 1.0). The results are compared depending on the methods of nanopowder synthesis.

Nanosized La1–xDyxPO4 · nH2O powders are synthesized by the sol-gel method using direct and reverse precipitation. The formation of a continuous series of hexagonal solid solutions based on LaPO4 · nH2O is confirmed by the XRD and DSC/TG methods. A continuous series of monoclinic solid solutions based on LaPO4 is formed at temperatures higher than 600°C. A reflex corresponding to a tetragonal form of DyPO4 is formed during the calcination of DyPO4 powder at 850°C. Two types of solid solutions are observed at temperatures of 1000–1200°C, namely, monoclinic solutions based on LaPO4 (to x ≈ 0.7) and tetragonal solutions based on DyPO4 (0.90 ≤ x ≤ 1.0). The results are compared depending on the methods of nanopowder synthesis.

The results of the study of novel composite solid electrolytes based on the CаO–Bi2O3–Fe2O3 system are presented. These materials have a mixed electronic-ionic conductivity which increases with the growth of the Fe2O3 content. In the (СаO)0.26(Bi2O3)0.74–Fe2O3 section, a part of the oxygen-ionic component increases with an increase in the Fe2O3 content and, in contrast, the oxygen conductivity decreases in the (СаO)0.2(Bi2O3)0.8–BiFeO3 section. These materials are interesting in terms of their use as elements of electrochemical devices, for example, in solid oxide fuel cells, electrolyzers for obtaining extra pure gases (oxygen, hydrogen), and electrochemical oxygen sensors.

A series of physical–chemical studies of a series of binary REE orthophosphate systems has been performed: LaPO 4 –DyPO 4 –H 2 O, LaPO 4 –YPO 4 –H 2 O, LaPO 4 –LuPO 4 –H 2 O, YPO 4 –LuPO 4 –H 2 O, and YPO 4 –ScPO 4 –H 2 O. Nanopowders of Ln' 1 −x Ln' x PO 4 · n H 2 O orthophosphates have been synthesized by the sol–gel method using direct and reverse precipitation techniques. Ceramic samples were produced from the nanopowders, and their physical–mechanical properties were determined depending on the thermal treatment temperature and duration. The ceramic samples’ thermal behavior has been investigated by the dilatometry method. The results have been compared depending on the technique of nanopowder synthesis.

Study of the phase formation in the systems TiO2‒MO(M2O3)‒KOH‒H2O (M = Mg, Ni, Al) from crystalline and coprecipitated X-ray-amorphous mixtures demonstrated that doped potassium titanate nanotubes can be obtained in a hydrothermal treatment of coprecipitated hydroxides in the temperature range 170‒220°C. The average outer diameter of the thus synthesized nanotubes strongly depends on the element being introduced and is 5 to 10 nm. The nanotubes have a large specific surface area (200‒300 m2 g‒1) and are stable up to a temperature of 500°C, above which they decompose to give potassium hexatitanate. The nanotubes can be used as sorbents, photocatalysts, and components of composite materials for frictional and construction purposes.

The results of a physicochemical study of hollandite-type minerals synthesized by the citrate-nitrate sol-gel method in the K2O-M2O3-TiO2 systems (M = Ga, Fe, Cr) and subjected to leaching in a mixture of hydrogen peroxide and sulfuric acid are reported. The materials thus prepared are stable up to 400°C and decompose above this temperature. The experiments performed confirm a decrease in the potassium content of these triple oxides upon such chemical treatment by 26–36% of the initial level, which makes these oxides promising for use as electrode materials for lithium-ion batteries.

Nanopowders of orthophosphate LaPO4-YPO4-H2O system have been synthesized via the solgel method, and the limits of the mutual solubility of components have been specified through the calculation of the parameters of the unit cell. The dense ceramics were prepared based on the La1 − x Y x PO4 · nH2O nan-opowders at 1000 and 1200°C. The porosity, microhardness, and bending strength of the ceramics were determined, and the dependence of the microhardness on the calcination time was established. The thermal behavior of the samples was studied by dilatometric method and the thermal coefficient of linear expansion of the ceramics was estimated.

A new method of sol–gel synthesis has been proposed for fabrication of functional materials with ramsdellite and hollandite types of crystal structure in the following oxide systems: Me2O–Me′2O3–Me″O2 (Me = Li, K; Me′ = Ga, Cr, Fe, In; Me″ = Ti, Sn). The formation of titanates with ramsdellite-type structure is shown to achieve at the temperature range of 250–650 °C, when gel combustion occurs. This allows fabrication of materials with high specific surface area. The ramsdellite phases and stannate hollandites are shown to form in the temperature range of 1,100–1,150 °C. Thus our method gives the possibility to reduce the thermo-temporal parameters of synthesis for this class of materials.

The results of experimental studies of synthesis of the hollandite phase K 2 Ga 2 Ti 6 O 16 using initial mixtures of different dispersion compositions obtained by two methods, i.e., mechanical dispersion (MD) (followed by solid-phase sintering) and sol-gel method (Pechini method, MP), are reported. The catalytic properties of the obtained materials in the reactions of carbon monoxide (CO) and hydrogen (H 2 ) oxidation have been determined. It has been demonstrated that an increase in the catalytic activity in the CO oxidation reaction is observed on the samples obtained using the sol-gel method, in which the hollandite phase content is higher and crystallization is more complete. The samples obtained using the MD method are characterized by a low porosity and activity in comparison with those produced by the Pechini method.

Nanopowders of lanthanum and yttrium orthophosphates have been synthesized. The growth of nanocrystals has been investigated in the temperature range 200–1100°C. The temperature-concentration limits of the existence of the solid solutions have been determined. The thermal behavior of the orthophosphates has been studied over the entire range of lanthanum and yttrium concentrations.

Powders of nanosized particles of individual and mixed lanthanum and lutetium orthophosphates are synthesized. The grain growth process is studied in the temperature range of 200–1100°C. Temperature and concentration regions of existence of the solid solutions based on hexagonal and monoclinic forms of LaPO 4 as well as on tetragonal LuPO 4 are determined.

Nanocrystals of yttrium lutetium phosphates of the general formula Y 1− x Lu x PO 4 · n H 2 O are synthesized. The temperature dependence of the nanocrystal size is investigated in the range 200–1100°C. The formation of a series of continuous solid solutions belonging to the tetragonal crystal system is revealed, and the limits of their thermal stability are determined.