A. A. Rempel

Russian Academy of Sciences, Moskva, Moscow, Russia

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Publications (141)187.73 Total impact

  • Mendeleev Communications 11/2014; · 1.05 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). · 0.38 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. · 2.30 Impact Factor
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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 01/2014; 50(4). · 0.38 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 01/2014; 56(3). · 0.77 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. · 0.77 Impact Factor
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    ABSTRACT: The electronic structure and stability of three phases of titanium monoxide TiOy with B1 type of the basic structure have been studied. Cubic phase without structural vacancies, TiO, and two phases with structural vacancies, monoclinic Ti5O5 and cubic disordered TiO1.0, was treated by means of first-principles calculations within the density functional theory with pseudo-potential approach based on the plane wave's basis. The ordered monoclinic phase Ti5O5 was found to be the most stable and the cubic TiO without vacancies the less stable one. The role of structural vacancies in the titanium sublattice is to decrease the Fermi energy, the role of vacancies in the oxygen sublattice is to contribute to the appearance of Ti–Ti bonding interactions through these vacancies and to reinforce the Ti–Ti interactions close to them. Listed effects are significantly pronounced if the vacancies in the titanium and oxygen sublattices are associated in the so called “vacancy channels” which determine the formation of vacancy ordered structure of monoclinic Ti5O5-type.
    Journal of Solid State Chemistry 08/2013; 204:146–152. · 2.04 Impact Factor
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    ABSTRACT: Quantum-mechanical ab initio calculations are used to simulate the free energy functions for titanium monoxide TiOy . The effect of the long-range order of the Ti5O5 type superstructure on the internal energy of the compound is studied by the supercell method. The dependences of the configuration entropy and free energy on the long-range order parameter are determined. It is found that the order-disorder phase transition in titanium monoxide must occur in accordance with the mechanism of the first-order phase transition with a critical value of the long-range order parameter of 0.971. The calculated parameters of the phase transition are compared with the experimental data and the results obtained using the model of point charges and by calculating the Madelung energy. It is concluded that the short-range order and the phonon entropy must be taken into account in calculating the equilibrium phase diagrams for strongly nonstoichiometric compounds.
    Journal of Experimental and Theoretical Physics 06/2013; 116(6). · 0.92 Impact Factor
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    ABSTRACT: The coincident Doppler broadening of the positron-electron annihilation radiation has been applied for the identification of vacancies in nano lead sulfide (nano-PbS) powders. The results of the positron annihilation studies on nano-PbS with different particle size are presented. Nano-PbS specimens have been synthesized by the chemical bath deposition in aqueous medium. Independently of the size of nanoparticles (from 12 to 16 nm) the positron lifetime (PLT) for all specimens has been found to be the same and equal to 391±1 ps. Independently of the size of nanoparticles the chemical surrounding of positron annihilation sites identified by coincident Doppler broadening measurements was the same, namely lead (Pb).
    Journal of Physics Conference Series 06/2013; 443(1):2013-.
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    ABSTRACT: Reactions of 2-ethoxymethylidene derivs. of 1,3-dicarbonyl compds. with N,N-dimethylethane-1,2-diamine gave a no. of 2-[(2-dimethylaminoethyl)amino]methylidene-1,3-dicarbonyl compds. which were subjected to regioselective quaternization at the tertiary nitrogen atom with Me iodide. The resulting quaternary ammonium salts inhibited aggregation of cadmium and zinc sulfide sols in aq. medium
    Russian Journal of Organic Chemistry 03/2013; 49(3):315-320. · 0.51 Impact Factor
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    ABSTRACT: The electron structures and formation enthalpies of vacancy-free cubic TiO, vacancy-ordered monoclinic Ti5O5, and vacancy-disordered cubic TiOy have been investigated using DFT+GGA calculations. Ti5O5 was found to be the stablest phase and TiO was found to be the least stable. The reason for the stability of the titanium and oxygen vacancies in the basic B1 structures of Ti5O5 and TiOy has been deduced. The titanium vacancies lead to a decrease in the Fermi energy. Oxygen vacancies cause strengthening in covalent Ti-Ti bonding.
    Bulletin of the Russian Academy of Sciences Physics 03/2013; 77(3).
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    ABSTRACT: Template synthesis of titania was conducted in solutions of polysaccharides, xanthan and sodium hyaluronan, prepared in ethylene glycol and on cellulose fibrils placed in ethylene glycol. The process was controlled by the addition of water in amounts sufficient only for the hydration of polysaccharides. When the precursor of TiO2, tetra(isopropyl) orthotitanate, was added, the fast reactions of hydrolysis and condensation were triggered only after its contact with water, which provided the precipitation of titania on xanthan and sodium hyaluronan macromolecules or on cellulose fibrils. The morphology of the synthesized TiO2 samples depended on the reagent concentrations in a reaction mixture. Amorphous titania was transformed by calcination into the crystalline state. Some of the obtained TiO2 samples have rather high photocatalytic activity comparable to that of the commercial photocatalysts.
    Russian Chemical Bulletin 01/2013; 62(4). · 0.42 Impact Factor
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    ABSTRACT: Cadmium sulfide quantum dots have been synthesized by wet chemical deposition from an aqueous solution. The sizes of the quantum dots determined by dynamic light scattering directly in the colloidal solution and by intermittent-contact atomic force microscopy in the dry sediment agree with each other. It has been found that splitting of the fluorescence peaks of the quantum dots can be affected by the disorder of the atomic structure of cadmium sulfide quantum dots.
    Physics of the Solid State 01/2013; 55(3). · 0.77 Impact Factor
  • A. Rempel’, N. Kozhevnikova, S. Rempel’
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    ABSTRACT: The structure of cadmium sulfide (CdS) micelle in stable aqueous solution of ethylenediaminetetraacetic acid was determined by dynamic light scattering, small-angle X-ray scattering and neutron scattering. The micelle aggregate is a single CdS nanoparticle with an average size of about 3 nm, the nanoparticle organic shell and the solvation shell are about 1 nm and 5 nm thick, respectively. These parameters were confirmed by the scanning semi-contact atomic force microscopy and powder X-ray diffraction studies of dry micelle cores isolated by high-speed centrifugation. The CdS micelle was correctly described by a simple double-shell model and was found to possess the structure corresponding to CdS quantum dots.
    Russian Chemical Bulletin 01/2013; 62(2). · 0.42 Impact Factor
  • Doklady Physical Chemistry 01/2013; 453(1). · 0.49 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 01/2013; 49(10). · 0.38 Impact Factor
  • M. G. Kostenko, A. A. Rempel
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    ABSTRACT: A method for calculating the probabilities of cluster configurations in ordered superstructures of strongly nonstoichiometric compounds depending on the composition and the order parameter is described using the Ti{sub 5}O{sub 5} superstructure of nonstoichiometric titanium monoxide TiO{sub y}. Analytic expressions are derived for the dependences of the probabilities of the main cluster configurations in the Ti{sub 5}O{sub 5} superstructure on the fraction of atomic positions in the titanium and oxygen sublattices and on the long-range order parameter. The probabilities of configurations are calculated for various long-range order parameters taking into account experimental data on the concentration of structural vacancies in the titanium and oxygen sublattices. The dependences of the probabilities of cluster configurations on the short-range order parameter are established from the relations between the superstructure long-range and short-range order parameters.
    Journal of Experimental and Theoretical Physics 12/2012; 115(6). · 0.92 Impact Factor
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    Doklady Physical Chemistry 11/2012; 447(1). · 0.49 Impact Factor
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    Doklady Chemistry 01/2012; 443(1):86–90. · 0.39 Impact Factor
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    ABSTRACT: The analytical dependence of cluster configuration probabilities on the vacancy concentrations and the long range order parameters for the TiOy, Ti5O5, Ti3O2, Ti2O3 and Ti4O5 phases of titanium monoxide has been calculated for the first time.
    Mendeleev Communications 01/2012; 22(5):245–247. · 1.05 Impact Factor

Publication Stats

467 Citations
187.73 Total Impact Points

Institutions

  • 1996–2014
    • Russian Academy of Sciences
      • • Institute of Chemistry
      • • Institute of Metal Physics
      Moskva, Moscow, Russia
  • 2010
    • Institute of Solid State Chemistry and Mechanochemistry
      Novo-Nikolaevsk, Novosibirsk, Russia
  • 1998–2002
    • Universität Stuttgart
      • Institute for Theoretical and Applied Physics
      Stuttgart, Baden-Württemberg, Germany