Browsing by Author "Iordanova R.S."

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    Effects of mechanical activation on structure and photocatalytic properties of ZnO powders
    (2013-11-01) Gancheva M.N.; Iordanova R.S.; Dimitriev Y.B.; Avdeev G.V.; Iliev T.C.
    Zinc oxide (ZnO) was mechanically activated in air using a planetary ball mill using varying milling speeds and time. The obtained samples were analyzed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and UV-Vis diffusion reflectance spectroscopy. The photocatalytic activity of the mechanically treated ZnO powders were investigated in the reaction of Malachite Green (MG) degradation in aqueous solution under UV-light irradiation. A decrease in the crystallite size (from 90 to 10 nm) accompanied by an increase of microstrains and lattice parameters were established applying different milling speeds. The agglomeration of the particles was observed by SEM analysis. The absorption spectra of the initial and mechanically activated ZnO samples show shifting of the band position from 360 to 330 nm, which can be related to decrease in the crystalline size. The ZnO powders activated at lower milling speeds (for shorter time intervals) exhibit highest photocatalytic activity. [Figure not available: see fulltext.] © 2013 Versita Warsaw and Springer-Verlag Wien.
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    Effects of mechanical activation on structure and photocatalytic properties of ZnO powders
    (2013-11-01) Gancheva M.N.; Iordanova R.S.; Dimitriev Y.B.; Avdeev G.V.; Iliev T.C.
    Zinc oxide (ZnO) was mechanically activated in air using a planetary ball mill using varying milling speeds and time. The obtained samples were analyzed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and UV-Vis diffusion reflectance spectroscopy. The photocatalytic activity of the mechanically treated ZnO powders were investigated in the reaction of Malachite Green (MG) degradation in aqueous solution under UV-light irradiation. A decrease in the crystallite size (from 90 to 10 nm) accompanied by an increase of microstrains and lattice parameters were established applying different milling speeds. The agglomeration of the particles was observed by SEM analysis. The absorption spectra of the initial and mechanically activated ZnO samples show shifting of the band position from 360 to 330 nm, which can be related to decrease in the crystalline size. The ZnO powders activated at lower milling speeds (for shorter time intervals) exhibit highest photocatalytic activity. [Figure not available: see fulltext.] © 2013 Versita Warsaw and Springer-Verlag Wien.
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    Influence of heat treatment on the phase transition of ZrMo 2O8 and photocatalytic activity
    (2011-06-01) Mancheva M.N.; Iordanova R.S.; Dimitriev Y.B.; Tyuliev G.G.; Iliev T.C.
    ZrMo2O7(OH)2 •2H2O was obtained from ZrOCl2•2H2O and Na2MoO 4•2H2O by a coprecipitation method. The phase and structural changes occurred during the heat-treatment of ZrMo2O 7(OH) 2•2H2O were investigated by XRD, IR and XPS analysis. The sequence of phase transformation can be divided into three stages: (1) transformation of ZrMo2O7(OH) 2•2H2O to orthorhombic LT-ZrMo2O 8 up to 300°C; (2) obtaining of mixture of both polymorphs of ZrMo2O8: cubic and trigonal at 400°C; (3) conversion to single trigonal (α) ZrMo2O8 above 450°C. The microstructure of the obtained trigonal (α) ZrMo2O8 was observed by scanning electron microscopy (SEM). The particle sizes were below 0.5 μm. The specific surface area was measured by modified BET method. The photocatalytic activity of the obtained trigonal (α) ZrMo 2O8 powders was investigated by degradation of a model aqueous solution of Malachite Green (MG) upon UV-light irradiation. © Versita Sp. z o.o.
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    Influence of heat treatment on the phase transition of ZrMo 2O8 and photocatalytic activity
    (2011-06-01) Mancheva M.N.; Iordanova R.S.; Dimitriev Y.B.; Tyuliev G.G.; Iliev T.C.
    ZrMo2O7(OH)2 •2H2O was obtained from ZrOCl2•2H2O and Na2MoO 4•2H2O by a coprecipitation method. The phase and structural changes occurred during the heat-treatment of ZrMo2O 7(OH) 2•2H2O were investigated by XRD, IR and XPS analysis. The sequence of phase transformation can be divided into three stages: (1) transformation of ZrMo2O7(OH) 2•2H2O to orthorhombic LT-ZrMo2O 8 up to 300°C; (2) obtaining of mixture of both polymorphs of ZrMo2O8: cubic and trigonal at 400°C; (3) conversion to single trigonal (α) ZrMo2O8 above 450°C. The microstructure of the obtained trigonal (α) ZrMo2O8 was observed by scanning electron microscopy (SEM). The particle sizes were below 0.5 μm. The specific surface area was measured by modified BET method. The photocatalytic activity of the obtained trigonal (α) ZrMo 2O8 powders was investigated by degradation of a model aqueous solution of Malachite Green (MG) upon UV-light irradiation. © Versita Sp. z o.o.