Browsing by Author "Stoyanova D."

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    ANTIMICROBIAL AND CYTOTOXIC PROPERTIES OF METAL NANOPARTICLES AND GRAPHENE MATERIALS (REVIEW)
    (2020-01-01) Ivanova I.A.; Stoyanova D.; Nenova E.; Kostadinova A.; Staneva A.
    The nanotechnology is the fastest developing branch of science in the border of physics, chemistry, biology and electronics. The ecological effect of nanomaterials on various organisms is still not enough understood. This review of the literature presents the mechanisms of action of nanomaterials: eluted metal ions, size and form of nanoparticles, reactive oxygen species and non-ionic interactions. The results obtained by different authors on the effects of graphene, metal nanoparticles, their oxides and nanocomposites on different types of organisms - prokaryotes and eukaryotes are described. Antimicrobial and cytotoxic properties of the new materials are discussed in respect to their medical and environmental significance
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    CORRELATION BETWEEN AGING TIME PERIOD OF METAL PRECURSOR SOL - PHASE COMPOSITION AND TEXTURAL PROPERTIES OF ZIRCONIA NANOPOWDERS
    (2024-01-01) Mitkova E.; Stambolova I.; Stoyanova D.; Toteva V.; Dimitrov O.
    This article investigates the effect of the time of aging of ZrO2 powders, obtained from zirconium butoxide sols, stabilized using complexating agents on the volume phase fractions tetragonal phase (T) and baddeleyite crystalographic phase (B), pore size distribution and pore volume. It was proved that the aging time period influences ratio between these two polymorphs of zirconia. The sample Zr3d possesses the largest content of baddeleyite phase having the greatest crystallites in comparison to another two powders. The increasing of aging period leads to a gradual increase in (101) peak intensity of T phase, while all the samples are microporous regardless of the aging time. The longest time aged sample possesses higher pore volume and higher average pore diameter than the other two powders. The physico-chemical features of the prepared ZrO2 nanosized powders could be beneficial as catalysts/photocatalysts in different catalytic reactions, corrosion inhibition particles, etc.
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    Slag-based materials as catalysts in oxidation reactions
    (2014-01-01) Mihajlova I.; Radoykova T.; Ivanov G.; Stoyanova D.; Mehandjiev D.
    The ability to create new active catalysts for complete oxidation of carbon monoxide and organic compounds on the basis of the metallurgical slag for waste gas purification was proven. The procedure for the synthesis of the catalysts includes only acid and thermal activation of the metallurgical slag, during which in addition to increasing the catalytic activity, the specific surface area is also increased several times. ICP-OES analysis, Differential thermal analysis (DTA), Thermogravimetric analysis (TGA), X-ray diffraction (XRD) measurements and Fourier transform infrared (FTIR) spec-troscopy have been used for the study of the composition and structure of the resulting materials, and the processes of phase formation. The textural properties and the chemical composition of the surface have been investigated by Scanning electron microscopy (SEM), BET analysis and X-ray photoelectron spectroscopy (XPS). The catalysts obtainedfrom metal-lurgical slag can be successfully used for purification of waste gases in industry and transport.