A. A. Rempel

Russian Academy of Sciences, Moskva, Moscow, Russia

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Publications (159)177.71 Total impact

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    ABSTRACT: A new approach for the synthesis of hybrid nanostructured titania–cadmium sulfide photocatalysts has been suggested. Photocatalysts TiO2 on CdS and CdS on TiO2 were characterized by various techniques including transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The photocatalysts have shown high activity in the partial oxidation of ethanol to acetaldehyde under the action of solar light (λ > 420 nm). The improved activity of the catalysts was attributed to the presence of heterojunctions between CdS and TiO2 nanoparticles that results in a more efficient charge separation as compared with pure CdS or TiO2. A better stability of the catalyst TiO2/CdS was likely due to the formation of a TiO2 protective coating on CdS nanoparticles.
    Catalysis Communications 08/2015; 68. DOI:10.1016/j.catcom.2015.04.034 · 3.32 Impact Factor
  • S.I. Sadovnikov, A.I. Gusev, A.A. Rempel
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    ABSTRACT: Chemical deposition from aqueous solutions of silver nitrate and sodium sulfide was used for synthesis of coarse-crystalline and nanocrystalline silver sulfide Ag2S powders. Sodium citrate was used as a complexing and stabilizing agent during synthesis. X-ray diffraction study shows that synthesized Ag2S powders have monoclinic (space group P21/c) α-Ag2S acanthite type crystal structure. The unit cell of artificial monoclinic silver sulfide Ag2S contains four Ag2S formula units and has the following parameters: a = 0.42264 nm, b = 0.69282 nm, c = 0.95317 nm and β = 125.554°. The size of silver sulfide particles in deposited powders was estimated by the X-ray diffraction and BET methods. By varying the ratio between the concentrations of reagents in the initial reaction mixture it is possible to deposit Ag2S nanoparticles with average size ranging in the interval from ∼1000 to ∼30 nm. Ag2S nanopowders have no deformation distortions of the crystal lattice practically because the microstrains ε in the synthesized powders do not exceed 0.15%. All the Ag2S powders with different particle size have an identical morphology.
    Superlattices and Microstructures 07/2015; 83. DOI:10.1016/j.spmi.2015.03.024 · 1.98 Impact Factor
  • S I Sadovnikov, A I Gusev, A A Rempel
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    ABSTRACT: Powders of silver sulfide have been synthesized by chemical bath deposition from aqueous solutions of silver nitrate and sodium sulfide in the presence of sodium citrate or EDTA-H2Na2. Colloid solutions have been prepared by a chemical condensation method from the same aqueous solutions. Synthesized silver sulfide nanopowders have a monoclinic (space group P21/c) acanthite-type structure but the occupancy of the metal sublattice sites by Ag atoms is smaller than 1. Unlike coarse-crystalline silver sulfide Ag2S, silver sulfide nanopowders with particles sizes of less than ∼50 nm are nonstoichiometric, contain vacant sites in the metal sublattice and have a composition of ∼Ag1.93S.
    Physical Chemistry Chemical Physics 04/2015; 17(19). DOI:10.1039/c5cp00650c · 4.20 Impact Factor
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    ABSTRACT: A method has been proposed for the simulation of the atomic structure of disordered phases of nonstoichiometric transition metal oxides, carbides, and nitrides with the B1 structure taking into account the short-range order in the arrangement of structural vacancies. The simplest structural models constructed with allowance for pair correlations between vacancies within the first four coordination spheres have been considered. A computer simulation of the atomic structure of disordered phases with the inclusion of the short-range order has been performed. For each structural model, the maximum possible concentration of vacancies and the short-range order parameters at different concentrations have been calculated. For a further experimental verification, the influence of the short-range order on the shape of the X-ray scattering spectrum has been investigated by calculating the theoretical X-ray diffraction patterns according to the Debye formula. The influence of the short-range order on the total energy of the disordered phases has been analyzed by ab initio methods. It has been shown that, in some cases, the proposed structural models of the short-range order are energetically favorable as compared to the model of statistical arrangement of vacancies.
    Physics of the Solid State 04/2015; 57(4):637-651. DOI:10.1134/S1063783415040137 · 0.78 Impact Factor
  • Yu. V. Kuznetsova, A. A. Rempel
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    ABSTRACT: We have studied the effect of disodium EDTA concentration on the size and zeta potential of CdS nanoparticles in a stable aqueous solution. Measurement results demonstrate that the colloidal solution remains stable at initial Cd2+ and S2− concentrations of 8 mM and initial EDTA concentrations in the range 3.2 to 16 mM. The reactant mixing sequence is shown to influence the ionic state of EDTA in solution, which in turn influences the stabilization mechanism of the CdS nanoparticles. At pH 3, we observe the formation of protonated chelates such as [CdHY]−, which may form a [-S-Cd-EDTA] ternary complex with the surface of a nanoparticle, thereby ensuring stability of the colloidal solution at a twofold excess of EDTA. Analysis of the nanoparticle size distribution evaluated by dynamic light scattering measurements indicates that the minimum hydrodynamic diameter of the nanoparticles is 10 ± 3 nm. The corresponding zeta potential is about −20 mV.
    Inorganic Materials 03/2015; 51(3):215-219. DOI:10.1134/S0020168515020119 · 0.51 Impact Factor
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    A. A. Valeeva, S. Z. Nazarova, A. A. Rempel
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    ABSTRACT: An in situ temperature study of a variation in the degree of long-range order in stoichiometric titanium monoxide has been performed by the magnetic susceptibility method. The measurements have been performed on annealed and quenched titanium monoxide in the temperature range from 300 to 1200 K. It has been found that the degree of long-range order depends on the regime and temperature of annealing of the initial samples. The degree of long-range order in the process of measurement of the magnetic susceptibility varies from 0.21 to 1.00; the larger the degree of long-range order, the smaller the magnetic susceptibility. Furthermore, the long-range order parameter decreases with an increase in the temperature above 1200 K and vanishes sharply at the order-disorder transition temperature. According to the results of this work, the critical long-range order parameter is 0.21 and the temperature of the nonequilibrium disorder-order transition is about 1073 K.
    JETP Letters 02/2015; 101(4):258-263. DOI:10.1134/S0021364015040141 · 1.36 Impact Factor
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    ABSTRACT: Manganese-doped zinc orthosilicate (Zn2SiO4:Mn) nanoparticles have been prepared using a sol-gel process followed by annealing. The doping level was varied widely: from 0.1 to 10 at % Mn. The average particle size of the as-prepared material was 20 nm. With increasing annealing temperature, the particle size increased, reaching 150 nm as evaluated by X-ray diffraction. The photoluminescence intensity in the material was shown to depend significantly on the phase composition of the samples, the degree of their crystallinity, and the doping level.
    Inorganic Materials 02/2015; 51(2). DOI:10.1134/S0020168515020156 · 0.51 Impact Factor
  • Mendeleev Communications 11/2014; DOI:10.1016/j.mencom.2014.11.007 · 1.15 Impact Factor
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    ABSTRACT: A method has been proposed for the synthesis of stable colloidal solutions of lead sulfide nanoparticles from aqueous lead acetate and sodium sulfide solutions. The citrate ion and ethylenediaminetetraacetic acid were used as complexing agents to stabilize the solution. The solutions obtained were shown to remain stable at room temperature for at least 30 days from the instant of synthesis, depending on the initial reactant concentration. According to X-ray diffraction and dynamic light scattering data, the stability and coagulation of the nanoparticles in solution were influenced by the lead and sulfur concentration, the presence of complexing agents, and the quantitative relation between the lead and complexing agent ions in solution. Optical absorption measurements for the colloidal PbS nanoparticle solutions showed that their absorbance was a nonlinear function of reactant concentration.
    Inorganic Materials 10/2014; 50(10). DOI:10.1134/S0020168514100148 · 0.51 Impact Factor
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    ABSTRACT: The challenges of the modern society and the growing demand of high-technology sectors of industrial production bring about a new phase in the development of organic synthesis. A cutting edge of modern synthetic methods is introduction of functional groups and more complex structural units into organic molecules with unprecedented control over the course of chemical transformation. Analysis of the state-of-the-art achievements in selective organic synthesis indicates the appearance of a new trend — the synthesis of organic molecules, biologically active compounds, pharmaceutical substances and smart materials with absolute selectivity. Most advanced approaches to organic synthesis anticipated in the near future can be defined as ‘atomic precision’ in chemical reactions. The present review considers selective methods of organic synthesis suitable for transformation of complex functionalized molecules under mild conditions. Selected key trends in the modern organic synthesis are considered including the preparation of organofluorine compounds, catalytic cross-coupling and oxidative cross-coupling reactions, atom-economic addition reactions, methathesis processes, oxidation and reduction reactions, synthesis of heterocyclic compounds, design of new homogeneous and heterogeneous catalytic systems, application of photocatalysis, scaling up synthetic procedures to industrial level and development of new approaches to investigation of mechanisms of catalytic reactions. The bibliography includes 840 references.
    Russian Chemical Reviews 09/2014; 83(10):885-985. DOI:10.1070/RC2014v083n10ABEH004471 · 2.58 Impact Factor
  • A. A. Rempel
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    ABSTRACT: The methods for synthesis of hybrid nanoparticles based on sulfides, oxides, and carbides of heavy and transition metals were considered. The problem of the influence of the method of synthesis of the hybrid nanoparticles on their atomic structure, morphology of the nanomaterials, and functional properties was analyzed. The areas of practical use of the hybrid nanoparticles were proposed.
    ChemInform 05/2014; 45(21). DOI:10.1002/chin.201421297
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    A. A. Valeeva, H. Schroettner, A. A. Rempel
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    ABSTRACT: Macrocrystalline niobium monoxide powder has been disintegrated to an average nanoparticle size of 20 ± 10 nm by high-energy milling in a planetary ball mill. X-ray diffraction data showed that, after milling, the particles retained an ordered cubic crystal structure with space group [TEX equation: Pm\bar 3m] , containing structural vacancies in both the metallic (25 at %) and nonmetallic (25 at %) sublattices. Analysis of diffraction line broadening as a function of the magnitude of the scattering vector indicated lattice strain anisotropy in the crystallographic directions [100], [110], and [111]. According to the diffraction line broadening data, the size of the nanoparticles in the [100] direction was smaller than those in the [110] and [111] directions. The use of surfactants enabled us to obtain a stable suspension of niobium monoxide nanoparticles in water.
    Inorganic Materials 04/2014; 50(4). DOI:10.1134/S0020168514040177 · 0.51 Impact Factor
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    ABSTRACT: The influence of the concentration of cadmium sulfide nanoparticles in a colloid aqueous solution on its optical properties has been investigated. The band gap of cadmium sulfide nanoparticles is calculated based on the optical absorption spectra of solutions with different concentrations. The band gap coincides for all the samples irrespective of their concentration and is equal to 2.63 eV. It is found that the intensity of fluorescence substantially depends on the solution concentration. The fluorescence intensity considerably decreases in a wavelength range from 665 to 720 nm as the concentration increases above 3.25 mM. This concentration is the threshold of the concentration quenching for CdS nanoparticles.
    Physics of the Solid State 03/2014; 56(3). DOI:10.1134/S1063783414030251 · 0.78 Impact Factor
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    ABSTRACT: Cellulose used for thousands of years has been rediscovered recently as a novel smart material for various nanotechnological applications. Its insoluble fibrils are functionalized by using mineralization methods developed in nanochemistry. Here they are coated by titania synthesized in one stage by a new green approach. It consists of controlling the localization of very fast hydrolysis and condensation reactions. Cellulose fibrils are placed in ethylene glycol with such an amount of water that is absorbed entirely by the hygroscopic polysaccharide. This hydrating water works as a reaction centre when the precursor reaches it. Instant hydrolysis and following condensation reactions proceeding mainly on the fibrils provide their mineralization. Titania prepared at ambient conditions is in an amorphous state. It is transferred in crystalline forms under a variety of conditions including moderate temperature (80 °C), calcination in air and cellulose carbonization in an inert atmosphere. These treatments result in photocatalytic activity. Even cellulose treated at the moderate conditions demonstrates significant self-cleaning ability consisting of fast degradation of methylene blue under outdoor sunlight irradiation. Photocatalytic activity of carbon–titania hybrids includes a side reaction of the oxidation of the carbonized fibrils. Photocatalytic properties of some of the calcinated samples, not containing organics, were comparable with a commercial photocatalyst.
    RSC Advances 01/2014; 5(12):8544-8551. DOI:10.1039/C4RA15862H · 3.71 Impact Factor
  • Doklady Physical Chemistry 11/2013; 453(1). DOI:10.1134/S0012501613110031 · 0.48 Impact Factor
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    ABSTRACT: Zn2SiO4:Mn (willemite) nanoparticles ∼30 nm in size have been prepared by disintegrating microcrystalline willemite powder in a planetary ball mill. X-ray diffraction and scanning electron micros-copy characterization showed that ball milling of the Zn2SiO4:Mn powder for 60 min or a longer time ensured complete disintegration of the microcrystalline material and that the crystal structure of the resultant nanoparticles was identical to that of the parent powder.
    Inorganic Materials 10/2013; 49(10). DOI:10.1134/S0020168513100087 · 0.51 Impact Factor
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    ABSTRACT: The electronic structure of nonstoichiometric titanium monoxide TiO y with different compositions y, which contains structural vacancies either in the metallic sublattice or in the nonmetallic sublattice, has been investigated using the supercell method within the DFT-GGA approximation with pseudopotentials. The cases of ordered and disordered arrangements of vacancies have been considered. It has been found that the complete removal of vacancies from the sublattice is energetically unfavorable, and the ordering of oxygen vacancies according to the type of the Ti6O5□1 superstructure, as well as titanium vacancies according to the Ti5▪1O6 type, does not lead to the stabilization of the B1 basic structure of titanium monoxide.
    Physics of the Solid State 10/2013; 55(10):2108-2115. DOI:10.1134/S106378341310017X · 0.78 Impact Factor
  • Doklady Chemistry 09/2013; 452(1):215-219. DOI:10.1134/S0012500813090024 · 0.35 Impact Factor
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    A. S. Kurlov, A. A. Rempel
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    ABSTRACT: The effect of cobalt powder morphology on the microstructure of WC-Co hard alloys produced by sintering cobalt + tungsten carbide powder mixtures has been studied using X-ray diffraction, laser diffraction, scanning electron microscopy, density measurements, and Vickers microhardness tests. The results indicate that, under identical sintering conditions, the densest and most homogeneous microstructure is formed in hard alloys sintered using cobalt powders consisting of rounded particles. The use of cobalt powders with dendritic morphologies impedes the homogenization of Co + WC powder mixtures and preparation of pore-free WC-Co hard alloys.
    Inorganic Materials 09/2013; 49(9):889-893. DOI:10.1134/S0020168513080086 · 0.51 Impact Factor
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    ABSTRACT: A model of the atomic structure with the short-range order in the vacancy distribution for the disordered cubic phase of titanium monoxide TiO1.0 has been proposed. The effect of the short-range order on the electronic structure and the stability of the compound has been studied by the supercell method within the DFT-GGA approximation with the use of pseudopotentials. It has been established that the appearance of the short-range order considerably decreases the total energy. The decrease in the energy is comparable with the energy gain during the ordering of the vacancies according to the type of monoclinic superstructure Ti5O5 to the long-range order parameter eta = 0.7. It has been shown that the discrepancies between the theoretical and experimental electronic spectra of titanium monoxide can be explained by allowance for the short range order.
    JETP Letters 08/2013; 97(11):616-620. DOI:10.1134/S0021364013110076 · 1.36 Impact Factor

Publication Stats

770 Citations
177.71 Total Impact Points

Institutions

  • 1988–2015
    • Russian Academy of Sciences
      • • Institute of Chemistry
      • • Institute of Solid State Chemistry, Ural Branch
      Moskva, Moscow, Russia
  • 2012–2014
    • Ural Federal University
      Sverolovsk, Sverdlovsk, Russia
  • 2011
    • Institute of Solid State Physics RAS
      Chernogolovka, Moskovskaya, Russia
  • 2010
    • Institute of Solid State Chemistry and Mechanochemistry
      Novo-Nikolaevsk, Novosibirsk, Russia
  • 2008
    • Ural State Technical University
      Sverolovsk, Sverdlovsk, Russia
  • 1998–2003
    • Universität Stuttgart
      • • Institute of Theoretical Physics
      • • Institute for Theoretical and Applied Physics
      Stuttgart, Baden-Württemberg, Germany