Browsing by Author "Mladenova B."
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Item MICROWAVE-ASSISTED SYNTHESIS OF SILVER NANOPARTICLES AS CATALYST FOR AIR GAS-DIFFUSION ELECTRODES(2022-01-01) Mladenova B.; Stankulov T.; Stankov S.; Boukoureshtlieva R.; Momchilov A.; Karsheva M.; Hinkov I.In this work, silver nanoparticles were synthesized from silver nitrate aqueous solution by using microwave irradiation. The morphology of the synthesized nanoparticles was studied by UV-Vis spectroscopy and by transmission electron microscopy showing spherical shapes with diameters of about 10 nm. The X-ray diffraction analysis exhibits their crystalline nature with face-centered cubic structure. Afterward, silver nanoparticles were integrated into activated carbon Norit NK to obtain catalytic composites. These composites were incorporated in the active layer of air gas-diffusion electrodes in order to study the catalytic activity for oxygen reduction reaction. For this purpose, a non-aggressive electrolyte solution of NaCl was used as an electrolyte. The obtained electrochemical results show a stable operation of all electrodes. Higher performance was found for composites containing 2 % wt. silver nanoparticles.Item Plant mediated synthesis of silver nanoparticles using extracts from Tilia cordata, Matricaria chamomilla, Calendula officinalis and Lavandula angustifolia flowers(2018-01-01) Mladenova B.; Diankov S.; Karsheva M.; Stankov S.; Hinkov I.In this work, a simple, rapid and efficient green method for silver nanoparticles synthesis was developed by using extracts from four medicinal plants: flowers of Tilia cordata, Matricaria chamomilla, Calendula officinalis and Lavandula angustifolia, acting as reducing and capping agents. Silver nitrate was used as a precursor. The effect of the sunlight exposure and/or the sonication treatment on the synthesis process was investigated. The ultraviolet-visible spectroscopy (UV-Vis) studies showed surface Plasmon resonance peaks between 432 nm and 448 nm, characteristic of spherical silver nanoparticles. The morphology of the nanoparticles produced was investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The proposed method could be easily implemented for any kind of scientific or industrial application due to its cost effective nature.Item SILVER NANOPARTICLES INCORPORATED INTO POROUS COLLAGEN SCAFFOLDS(2022-01-01) Samichkov V.; Mladenova B.; Diankov S.; Foteva T.; Hinkov I.In this work, we present a simple, rapid and cost-effective microwave-assisted method for silver nanoparticles synthesis by chemical reduction using an aqueous solution of silver nitrate, ethanol and ammonia. The effect of reagent concentrations and the heating time was investigated. Samples were analyzed through UV-Vis spectroscopy and transmission electron microscopy. Furthermore, the obtained silver nanoparticles were mixed with collagen dispersions to prepare porous scaffolds by vacuum-sublimation drying. Silver nanoparticles can adhere to the bacterial cell wall subsequently causing its death. The microbiological study showed that the collagen scaffolds with incorporated silver nanoparticles exhibited antibacterial activity against Bacillus subtilis NBIMCC 3562 and Escherichia coli NBIMCC 407 bacteria and could find potential applications in medicine.