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Effects of mechanical activation on structure and photocatalytic properties of ZnO powders

100%
Gancheva M., Iordanova R., Dimitriev Y., Avdeev G., Iliev T.
Open Chemistry
|
2013
|
vol. 11
|
issue 11
1780-1785
EN
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. [...]
2
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Influence of heat treatment on the phase transition of ZrMo2O8 and photocatalytic activity

100%
Mancheva M., Iordanova R., Dimitriev Y., Tyuliev G., Iliev T.
Open Chemistry
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2011
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vol. 9
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issue 3
460-465
EN
ZrMo2O7(OH)2·2H2O was obtained from ZrOCl2·2H2O and Na2MoO4·2H2O by a coprecipitation method. The phase and structural changes occurred during the heat-treatment of ZrMo2O7(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-ZrMo2O8 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) ZrMo2O8 powders was investigated by degradation of a model aqueous solution of Malachite Green (MG) upon UV-light irradiation.
3
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Photocatalytic properties of ZnO/TiO2 powders obtained via combustion gel method

86%
Bachvarova-Nedelcheva A., Iordanova R., Stoyanova A., Gegova R., Dimitriev Y., Loukanov A.
Open Chemistry
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2013
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vol. 11
|
issue 3
364-370
EN
Abstract The present study is a continuation of our previous investigations on the ZnO-TiO2 system. By applying different sol-gel methods we proved that the type of precursor and the order of adding the components influence the microstructure of the final product. This study focuses on the combustion sol-gel synthesis and photocatalytic properties of nanosized (∼7-20 nm) ZnO-TiO2 powders. The photocatalytic tests were performed toward two model organic dyes, Malachite Green and Reactive Black 5, in the UV and Vis region. For synthesis of ZnO/TiO2 powders, different precursors such as Zn(NO3)2·6H2O, Zn(CH3COO)2·2H2O, Ti(OC2H5)4 and Ti(OC4H9)4 were used. During the combustion process various phases (ZnO, TiO2 - anatase and rutile, ZnTiO3) were obtained. The structure and morphology of the resulting particles were characterized by XRD and SEM analysis. All samples exhibited a good photocatalytic activity in both UV and Vis regions. Graphical abstract [...]
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