Browsing by Author "Stambolova I."

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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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    Nitric acid activation of La-doped ZnO photocatalyst for water decontamination
    (2015-01-01) Milenova K.; Eliyas A.; Blaskov V.; Stambolova I.; Vassilev S.; Rakovsky S.; Kasabova N.
    An original patented procedure was applied to obtain activated ZnO powder and then it was doped with 1.5 mass % La to improve the photocatalytic performance. The effect of a nitric acid treatment (index a.t.) of the La/ZnO investigated by comparing with the non-treated La/ZnO samples, manifests a higher photocatalytic efficiency of the former in the oxidative degradation of the model textile wastewater pollutant azo dye Reactive Black 5. The acidically treated La/ZnO powders have been obtained by impregnation in 0.1 M HNO3 acidic solution, followed by thermal treatment at 100oC, 350°C and 500°C. The materials have been characterized by the XRD, XPS and single point BET methods. The XRD analysis shows the presence of three crystallographic phases: wurtzite, Zn(NO3)(OH).H2O and 4ZnO(OH)2.Zn(NO3)2.H2O. The XPS data give evidence of N-atoms in ZnO after the acidic treatment. The best photocatalytic performance is shown by the La/ZnO a.t. dried at 100°C due to its highest nitrogen content.
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    The influence of nd and sm on the structure and properties of sol-gel-derived tio2 powders
    (2021-07-01) Bachvarova-Nedelcheva A.; Yordanov S.; Iordanova R.; Stambolova I.; Stoyanova A.; Georgieva N.; Nemska V.
    TiO2 nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300◦C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400◦C). The TiO2 (rutile) was not detected up to 700◦C in the presence of both modified oxides. TiO2 (anatase) crystals found at about 400◦C in the Sm-modified sample exhibited an average crystallite size of about 25–30 nm, while doping with Nd resulted in particles of a lower size—5–10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240–350◦C. Photocatalytic tests showed that the samples heated at 500◦C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.
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    Visible light photocatalytic activity of TiO2 deposited on activated carbon
    (2013-03-01) Eliyas A.; Ljutzkanov L.; Stambolova I.; Blaskov V.; Vassilev S.; Razkazova-Velkova E.; Mehandjiev D.
    Four photocatalyst samples, prepared from beech sawdust, were synthesized by an original method, combining pyrolysis and impregnation - two of them: TiO2 + activated carbon and other two - only activated carbon. The pyrolysis process has been carried out at two different temperatures - 680 C and 830 C. The prepared samples were characterized by a series of methods - XRD, BET, SEM and DTA/TG. The most important result was achieving visible light photocatalytic activity with an azo dye pollutant for both materials. The TiO2/AC-680 C sample demonstrated higher activity under visible light illumination than the TiO2/AC-830 C sample. The visible light activity was attributed to the active carbon component in the composite materials, which was evidenced by the photocatalytic tests with bare carbon (without any TiO2) manifesting visible light activity. The AC-680 C carbon was superior to the AC-830 C under visible illumination probably due to its higher specific surface area and porous texture. UV-light testing of the photocatalytic activity revealed that the TiO2/AC-680 C sample was higher than that of the TiO2/AC-830 C under polychromatic UV-A illumination (320-400 nm with a maximum at l = 365 nm). The TiO 2/AC-680 C sample was also more efficient with the monochromatic UV-C illumination (l = 254 nm). © 2012 Versita Warsaw and Springer-Verlag Wien.