Browsing by Author "Dimitrova S."

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    Effect of the thermal treatment on the Pb (II) adsorption ability of blast furnace slag
    (2013-05-21) Mihailova I.; Dimitrova S.; Mehandjiev D.
    The aim of this study is to evaluate the possibilities for improving the adsorption capacity of blast furnace slag in processes for removal of heavy metal ions from aqueous media. Three samples of slag have been prepared by heating of granulated blast furnace slag. The initial slag and thermally treated slag samples have been characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and BET analysis. It has been found that the main crystalline phase of the analyzed slag samples is melilite. Merwinite and pseudowollastonite have been also identified. The Pb(II) adsorption isotherms have been obtained under bath conditions. All samples demonstrate a good Pb(II) removal ability. The equilibrium adsorption data are described by the Langmuir model. The highest Pb(II) adsorption capacity has been achieved by the blast furnace sample treated at 860 °C. The obtained results suggest that it is possible to improve the adsorption properties of blast furnace slag and slag based materials, by control of the phase composition.
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    Immobilization of zinc phthalocyanines in silicate matrices and investigation of their photobactericidal effect on E. coli.
    (2006-01-01) Artarsky S.; Dimitrova S.; Bonnett R.; Krysteva M.
    The aim of the present investigation was to immobilize zinc phthalocyanines in a silicate matrix and to test the photobactericidal properties of the matrices so prepared toward Esherichia coli in model aqueous media. For the purpose, tetra tertiary butyl zinc phthalocyanine (TBZnPc) and zinc phthalocyanine tetrasulfonic acid (ZnPcTS) were used. The abilities of these two photosensitizers to generate singlet oxygen in solution were compared by following the rate of photobleaching of 1,3-diphenylisobenzofuran (DPBF) at 430 nm in dimethylformamide (DMF). The results of this study show clearly that, under the conditions used here, the TBZnPc is the more effective generator of singlet oxygen; with it the DPBF was virtually completely photobleached in 4 min, while with the ZnPcTS under the same conditions, it took 12 min to reach this point. Glass conjugates with the two phthalocyanines were obtained by the sol-gel technique and were characterized by a well-defined color due to the phthalocyanine incorporated in the silicate matrix. Glasses with an intense, but inhomogeneous, green color were obtained when the tetrasulfonic derivative of the zinc phthalocyanine was used, while blue glasses of evenly distributed coloration were formed from the tetra tertiary butyl derivative. The ZnPcTS conjugate demonstrates more effective singlet oxygen evolution than is the case with the TBZnPc conjugate. These results are the opposite of those obtained for the free phthalocyanines in solution. The structural formulae of the compounds show that TBZnPc has a more pronounced hydrophobic character than the sulfonic derivative. In our view, the relative reactivities of the conjugates can be explained by the tetrasulfonic derivative being situated mainly in the surface parts of the glass matrix where the hydrophilic character is prevailing, while the tertiary butyl derivative is mainly present in the internal parts of the matrix as a result of which it is less accessible and therefore less active. The results obtained on the effect of zinc phthalocyanine conjugates on E. coli show a trend similar to that observed with singlet oxygen evolution shown. Thus, for the ZnPcTS conjugate, the log kill is 1.32 and for the TBZnPc conjugate, it is 0.98, in each case after 120 min. The results obtained show that phthalocyanines can be immobilized successfully in a silicate matrix and used for photodisinfection of microbially polluted waters. The silicate matrix has some advantages in comparison with other organic matrices. It is insoluble in water, resistant towards microorganisms, easy to fabricate, and might be developed successfully for the photodisinfection of water, e.g., in swimming pools and in other open water reservoirs.
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    Valorization of Peanut and Walnut Shells through Utilisation as Biosorbents for the Removal of Textile Dyes from Water
    (2023-08-01) Lazarova S.; Tonev R.; Dimitrova S.; Dimova G.; Mihailova I.
    The present research focuses on the application of peanut and walnut shells, in their natural state, for the removal of methylene blue (MB) from water solutions in batch and dynamic (flow-through) conditions. Under batch conditions, at a 100 mg/L MB concentration of aqueous solution, the optimum dose of the studied biosorbents was determined to be 2.5 g/L, reaching about 95–97% efficiency of MB removal for both materials. Langmuir and Freundlich isotherms were used to model and evaluate the experimental data under different initial concentrations of MB (25 to 100 mg/L). The determined maximum adsorption capacities are 41.50 mg/g for walnut shells and 46.80 mg/g for peanut shells. Under flow-through conditions, breakthrough curves are determined for three sizes of fractions (<0.25 mm, 0.315–0.5 mm, and 0.8–1.6 mm). For peanut shells, the smaller the particle size, the higher the adsorption capacity and the column breakthrough time. For walnut shells, however, the particle size seems to have a more complex influence on the adsorption process parameters, and this phenomenon deserves future investigation. The adsorption capacity for one and the same fraction size of 0.315–0.5 mm and initial MB concentration of 50 mg/L is higher under dynamic flow conditions, i.e., 51 mg/g compared to 20 mg/g for walnut shells and 46 mg/g compared to 17.5 mg/g for peanut shells.