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Chemical and technological characterization of medieval glass bracelets from South-East Bulgaria

100%
Georgieva R., Detcheva A., Dimitriev Y.
Open Chemistry
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2014
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vol. 12
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issue 11
1169-1175
EN
The present paper deals with chemical and physicochemical characterization of seven glass fragments of medieval glass bracelets from South-East Bulgaria. Samples were investigated by Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and differential thermal analysis (DTA). Gravimetric chemical analysis was used for silica assessment. Flame photometry was applied to determine sodium and potassium content while aluminium, calcium and magnesium were determined by flame atomic absorption spectrometry after dissolution using a mixture of acids. All investigated artefacts are soda-lime-silica glasses and when produced two different recipe norms were used. Important technological parameters of glass manufacturing were determined and discussed. This investigation throws light on the technological development and production of glass during medieval times.
2
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Effects of mechanical activation on structure and photocatalytic properties of ZnO powders

88%
Gancheva M., Iordanova R., Dimitriev Y., Avdeev G., Iliev T.
Open Chemistry
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2013
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vol. 11
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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. [...]
3
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Influence of heat treatment on the phase transition of ZrMo2O8 and photocatalytic activity

88%
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.
4
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Organic-inorganic hybrid materials based on N=C=O functionalised silan modified with titanium and zirconium

76%
Ivanova Y., Dimitriev Y., Gerganova T., Bryaskova R., Fernandes M., Miranda Salvado I.
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EN
This work investigates the influence of the precursor trimethylsilil isocyanate on the sol-gel synthesis of hybrid materials. The obtained Si−O−C−N network is additionally modified by titanium and zirconium alcoxypropoxides in the range of 10 to 30 wt. %. The structure of the obtained hybrid materials before and after pyrolysis up to 1100°C was investigated by methods of XRD, FTIR and 29Si MAS NMR. We established that the hybrid structure was stable up to 600°C based on IR study. The structural transformation of the hybrid materials into oxycarbonitrogen system started at 800°C. The network of the hybrids modified by titanium remained stable and amorphous up to the final temperature of the pyrolysis (1100°C) compared to the gels modified by more than 10 wt.% Zr. It was confirmed by XRD analysis that the last mentioned are nanocomposite materials, built from carbooxynitrogen vitreous matrix and ZrO2-nanocrystals (tetragonal). The NMR method verified the presence of heterometallic bonds (Si−O−Ti and Si−O−Zr) and Q4, ZrQ3 or TiQ3, NSiO3 and D structural units in the gels.
5
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Photocatalytic properties of ZnO/TiO2 powders obtained via combustion gel method

76%
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
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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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