Valeri P. Tolstoy

Synthesis of birnessite structure layers at the solution-air interface and the formation of microtubules from them.

H(x)MnO2·nH2O layers have been successfully produced through a facile low-temperature process at the solution-air interface without using any templates. The crystalline structures of layers can be tuned by the compositions and the pH of the growth solutions. The analysis of birnessite-like layers indicates that they are formed by nanosheets approximately 4-6 nm thick that are oriented for the most part normally to the interface. Our results demonstrated that 1-3-μm-thick layers can roll up into microtubules 20 to 100 μm in diameter and up to 10 mm long. The hypothesis explaining the formation of the microtubular structures is assumed.

Synthesis of LaF3 nanosheets with high fluorine mobility investigated by NMR relaxometry and diffusometry

Ionically conducting lanthanum fluoride (LaF3), displaying a nanoscopic lamellar structure, has been synthesized at the surface of an aqueous solution of LaCl3 and HF. The structure and the chemical composition of the conductor have been analyzed by SEM, electron probe microanalysis, X-ray powder diffraction, FTIR, and (19)F magic angle spinning nuclear magnetic resonance (NMR) spectroscopy. The fluorine dynamics have been studied by NMR diffusometry and relaxometry in a temperature range from room temperature up to 875 K. The fluorine self-diffusion coefficient of the nanostructured LaF3 is about two orders of magnitude larger than that of bulk LaF3. This novel material is highly promising for many typical applications of fluorine ionic systems.

Facile synthesis of scandium fluoride oriented single-crystalline rods and urchin-like structures by a gas–solution interface technique

A facile and effective method to obtain urchin-like structures and ordered arrays of rod-like crystals of scandium fluoride by an interfacial interaction between solution and gaseous reagents (Gas–Solution Interface Technique, GSIT) is reported. The rod crystals with tetragonal crystal lattice can be as thin as ca. 200 nm and as long as ca. 7 μm. The effect of solution concentration and reaction time on the morphology of the product is reported. The synthesized crystals were characterized by SEM, TEM, HRTEM, XRD analyses, EDS, XPS, and FT-IR spectroscopy. A hypothesis is proposed on the formation of rod crystals during the GSIT process.

A Novel Oxidation-Reduction Route for Layer-by-Layer Synthesis of Nanolayers and Investigation of Its Photocatalytical Properties

Layer-by-layer (LbL) synthesis of titanium dioxide was performed by an oxidation-reduction route using a Ti(OH)3 colloid and NaNO2 solutions. A model of chemical reactions was proposed based on the results of an investigation of synthesized nanolayers by scanning electron microscopy, electron microprobe analysis and X-ray photoelectron spectroscopy, and studying colloidal solution of Ti(OH)3 with laser Doppler microelectrophoresis. At each cycle, negatively charged colloidal particles of adsorbed onto the surface of substrate. During the next stage of treatment in NaNO2 solution, the particles were oxidized to Ti(OH)4. Photocatalytic activity was studied by following decomposition of methylene blue (MB) under UV irradiation. Sensitivity of the measurements was increased using a diffuse transmittance (DT) method. The investigation revealed strong photocatalytical properties of the synthesized layers, caused by their high area per unit volume and uniform globular structure.

Flower-like silver nanocrystals: facile synthesis via a gas–solution interface technique

In this paper, flower-like Ag nanocrystals and their fractal networks were successfully synthesized by gas–solution interface technique at the surface of AgNO3 water solution with the assistance of ammonium citrate and of gaseous N2H4 used as reductant. The synthesized flower-like silver structure consisted of a large number of petal-like silver nanoplates. They were characterized by scanning and transmission electron microscopy, absorption UV–Vis spectroscopy, and X-ray diffraction. In addition to the standard silver fcc modification, the nanostructures contained the hexagonal polymorph (4H-Ag) in the amount of about 5%. The effect of pH of the solution on the morphology of nanoparticles and on the silver crystal structure was examined. Depending on the time of treatment with gaseous hydrazine, it was possible to obtain either separate flower-like nanoparicles and their fractal networks, or continuous films formed by rather closely packed petal-like nanoparticles. The surface-enhanced Raman scattering effect was observed, and the most intense interaction of laser beam with the silver nanoparticles occurred when the solution side of the synthesized film was irradiated.

Interface-Assisted Synthesis of Single-Crystalline ScF3 Microtubes

Scandium fluoride (ScF3) microtubes with nanoscale wall thickness were for the first time successfully synthesized by an interface-assisted technique at the surface of a scandium nitrate aqueous solution without the addition of any surfactant as a result of interaction with hydrofluoric acid from the gaseous phase in only 30 min. X-ray diffraction analysis, scanning electron microscopy, helium ionic microscopy, transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) were used to examine the morphology and crystal structure of ScF3 microtubes. The results show that the ScF3 microtube is single-crystalline and has a hexagonal structure. A hypothetical model of thin-walled microtube formation is proposed.

Strong negative thermal expansion in the hexagonal polymorph of ScF3

A new hexagonal polymorph of scandium fluoride (ScF3) has been synthesized and thoroughly characterized. The new phase displays two types of negative thermal expansion in a wide temperature range at normal pressure: a relatively weak isotropic negative thermal expansion at low temperatures and a strong anisotropic negative thermal expansion above 500 K. The thermal behavior is explained in part by a model of static structure distortions.

Layer-by-layer synthesis of metal oxide (or hydroxide)-graphene nanocomposites. The synthesis of CuO nanorods-graphene nanocomposite

Principle conditions for layer-by-layer synthesis of nanocomposite films incorporating graphene and metal oxides or hydroxides are formulated in the paper. As an example of this method the synthesis of nanocomposite containing graphene nanosheets and copper oxide (II) nanorods is described. This material was first synthesized in our study using amminecuprate (II) solution and water suspension of graphene. Analysis of the synthesized thin films by SEM, XRD and Raman spectroscopy have shown that the size of the graphene nanosheets in the films is about 5u2005µm and the size of the cupric oxide nanorods with monoclinic crystalline structure is approximately 10-12 by 150-200u2005nm. Some recommendations are given concerning potential applications of these layers in the electrodes of electrocatalysts and electrochemical sensors.