Browsing by Author "Zahariev I."

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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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    Template synthesis and study of Co-Ni core/carbon shell nanoparticles
    (2017-01-01) Zahariev I.; Hristoforou E.; Markova I.
    Co-Ni core/carbon-based shell nanoparticles are synthesized at room temperature by the help of a template technique, using a carbon-containing support through a chemical reduction with 0.2 M NaBH4 in a mixture of aqueous solutions of 0.1 M CoCl2.6H2O and 0.1 M NiCl2.6H2O at a ratio Co:Ni=1:1. As a support of fluorinated graphite (CF) in the presence of β-cyclodextrine (β-CDx), or respectively N-Methyl-2-pyrrolidone (NMP) and N-acetyl-Dglucosamine (NAG), is used during the reduction process. Both Scanning electron microscopy (SEM) and Energy dispersitive spectroscopy (EDS) analyses are carried out to determine the morphology and surface elemental composition. The SEM images show that the synthesized core/shell nanoparticles are too small, but definitely spherical in shape. The particles are spheroidal assemblies, because of magnetic interaction forces. It is observed that the nanoparticles are deposited among the graphite grains and surrounded with the β-CDx, NMP and NAG molecules, respectively. The ratio Co:Ni = 1:1, set in the reaction solution, is exactly reproduced in the Co-Ni nanoparticles. The prepared hybrid core/shell nanoparticles are also investigated with X-ray diffraction (XRD) and Infrared spectroscopy with Fourier transformation (FTIR) in the mid-Infrared region (4000-400 cm-1). XRD analysis proves the formation of amorphous Co-Ni nanoparticles. FTIR spectra establish the existence of different chemical bonds such as O-H, C-O, C-H, C-N, B-O, B-H, Co-O, Ni-O in the corresponding atom groups situated on the nanoparticle surface.