Browsing by Author "Vassilev S."

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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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    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.