Browsing by Author "Piskin M."

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    Ftir spectroscopy method for investigation of Co-Ni nanoparticle nanosurface phenomena
    (2017-01-01) Zahariev I.; Piskin M.; Karaduman E.; Ivanova D.; Markova I.; Fachikov L.
    The Co-Ni nanoparticles examined are synthesized through a borohydride reduction with NaBH4 in aqueous solutions of chloride salts containing a different ratio of Co and Ni (1:1, 4:1 and 1:4, correspondingly) and also in the course of a template synthesis with graphite as a support in presence of β-cyclodextrin. The morphology, the elemental and phase composition of the synthesized Co-Ni nanoparticles are studied by SEM, EDS and XRD analyses. FTIR spectroscopy investigations carried out provide to elucidate the atom /molecule groups formed in the Co-Ni nanoparticles and their carbon-containing nanocomposites. The different shape and position of the bands of absorption at the relevant wavenumber [cm-1] identify the mode of vibrations (symmetric and asymmetric stretching and bending vibrations) of the created chemical bonds arising at the nanoparticle surface such as C-OH, CO-OH, C-H2, C=O, BO3, BO4, free OH, H-OH (H2O), CoO, NiO. The FTIR spectra reported illustrate also the effect of the different Co:Ni ratios studied and that of the support used. The data obtained show that FTIR spectroscopy is a sensitive method suitable for studying Co-Ni nanoparticles and their carbon-containing nanocomposites surface phenomena.
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    Spectroscopic study of the template synthesized intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles with a carbon support
    (2018-01-01) Markova I.; Piskin M.; Zahariev I.; Ivanova D.; Fachikov L.; Christoforou E.
    Intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles are synthesized through a borohydride reduction in a mixture of aqueous solutions of CoCl2.6H2O, NiCl2.6H2O and SnCl2.2H2O salts at room temperature applying a template technique. A carbon support is used. As a result nanocomposite materials are obtained in situ. The ratio of the metallic components is chosen on the ground of the phase diagrams of the relevant binary (Co-Sn, Ni-Sn, Co-Ni) systems: Co:Sn = 35:65, Ni:Sn = 45:55, Co:Ni = 50:50. Graphite and carbon powders are used as a carbon support. To avoid the nanoparticle's aggregation β-cyclodextrin is added to the reaction solutions. EDS and XPS investigation methods are applied to study the surface composition of the synthesized intermetallic nanoparticles and their carbon nanocomposites. A particle's morphology is typical for the alloyed materials. The nanoparticles are characterized by a relatively high specific surface area. Both the elemental and phase composition of the investigated particles and their carbon composites do not alter with the change of the carbon support. They depend only on the ratio between the respective metal components set in the starting reaction solutions according to the phase diagrams of the corresponding binary systems. The studies conducted on the intermetallic nanoparticles synthesized with various carriers demonstrate that they are suitable to be used as catalysts, electrode materials in Li-ion batteries and as magnetic materials for biomedical applications.
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    Synthesis and study of carbon-based nanocomposites with Co-Sn nanoparticles for electrode materials
    (2015-01-01) Milanova V.; Markova I.; Piskin M.; Stankulov T.; Petrov T.; Denev I.
    Intermetallic Co-Sn nanoparticles have been synthesized through a template borohydride reduction with NaBH4, using a carbon-containing support in a mixture of aqueous solutions of the corresponding chloride salts (CoCl2.6H2O and SnCl2.2H2O) at mass ratio Co:Sn = 35:65. The ratio is chosen in accordance with the Co-Sn binary system phase diagram. The ``template`` technique involves reductive precipitation of intermetallic nanoparticles on a support. Fluorinated graphite (CF) and graphite/β-cyclodextrin (Dx) hydrate have been used as supports. Subsequently, carbon polymer-based nanocomposites with Co-Sn nanoparticles have been obtained. The content of the polymer in the obtained nanocomposites varies between the samples. The reductive precipitation was carried out at room temperature and atmospheric pressure. Samples were studied by physic-chemical and electrochemical analyses. The morphology, structure, phase composition and surface element content of the prepared nanocomposites have been investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis. The nanocomposite morphology is typical for the alloy materials. CoSn2 and CoSn phases are formed according to the Co-Sn binary system phase diagram. The surface element composition has proven the existence of Co and Sn. Electrochemical study of these nanocomposite materials has been carried out by a cycling voltammetry. The samples are assembled in argon filled glove box and are electrochemically tested as electrode materials (anodes) in a Li-ion battery. The charge-discharge tests have shown that these nanocomposite materials, containing a CoSn2 phase, are characterized by a stable specific capacity after the 20 cycles, better cyclicibility and higher efficiency, as compared to the Co-Sn alloy. Their measured capacity is a reason to be an alternative replacement of the graphite electrodes in Li-ion batteries.