Browsing by Author "Milenova K."

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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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    Porous texture of CuO prepared from copper oxalate precursor
    (2006-07-01) Nickolov R.; Donkova B.; Milenova K.; Mehandjiev D.
    The porous texture of CuO obtained from CuC2O4 • 0.5H2O as a precursor, as well as the interconnection between the texture of the initial oxalate and that of the copper oxide obtained, has been studied by physisorption, XRD, XPS and SEM methods. The dimensions of the particle aggregates and the crystalline particles were altered as a consequence of the thermal decomposition of CuC2O4·0.5H2O to CuO, and this led to an increase of ca. 1.5-times in the specific surface of the CuO obtained relative to that of the initial substance. The comparatively non-uniform sizes of the intra-aggregate mesopores in CuC2O4·0.5H2O were transformed into considerably smaller intra-aggregate mesopores in CuO. A finite increase in the volume of the intra-crystallite pores in CuO was also observed, although this did not change the average size of the intra-crystallite pores in the oxide obtained nor the character of the pore-size distribution with respect to the starting material. In addition, as a result of the thermal decomposition of CuC2O4·0.5H2O, the mesoporosity of the prepared oxide also developed. However, the CuO component retained the textural type characteristic of the initial CuC2O4·0.5H2O.