Browsing by Author "Staneva A."
Now showing 1 - 20 of 24
Results Per Page
Sort Options
Item ANTIMICROBIAL AND CYTOTOXIC PROPERTIES OF METAL NANOPARTICLES AND GRAPHENE MATERIALS (REVIEW)(2020-01-01) Ivanova I.A.; Stoyanova D.; Nenova E.; Kostadinova A.; Staneva A.The nanotechnology is the fastest developing branch of science in the border of physics, chemistry, biology and electronics. The ecological effect of nanomaterials on various organisms is still not enough understood. This review of the literature presents the mechanisms of action of nanomaterials: eluted metal ions, size and form of nanoparticles, reactive oxygen species and non-ionic interactions. The results obtained by different authors on the effects of graphene, metal nanoparticles, their oxides and nanocomposites on different types of organisms - prokaryotes and eukaryotes are described. Antimicrobial and cytotoxic properties of the new materials are discussed in respect to their medical and environmental significanceItem BIOLOGICAL ACTIVITY OF GRAPHENE NANOCOMPOSITES WITH ZINC OXIDE, Cu AND Ag NANOPARTICLES(2023-01-01) Martinov B.; Pavlova E.; Ivanova I.A.; Yocheva L.; Kostadinova A.; Staneva A.The aim of this research is to obtain collagenе nanocomposites based on graphene, graphene oxide, GO, zinc oxide and metal nanoparticles and to evaluate their pro-, antioxidant and biological activities by luminescent and standard microbiological assays. The antimicrobial activity of graphene composites with added nanosized zinc oxide, silver and copper nanoparticles was tested on Firmicutes bacteria Staphylococcus epidermidis (ATCC 1228) and Gracillicutes Escherichia coli (ATCC 25922). The method of diffusion in agar was used in three variants - spot diffusion, well and paper-disc diffusion. The spot and diffusion disc approaches of the method have shown better effect than the well diffusion for testing the effect of graphene composites on bacteria. The composites with high ZnO content had the best antimicrobial properties against the tested bacteria. The cytotoxicity of the nanocomposites using normal MDCK and A549 epithelial sarcoma cells were tested for 24 h at a concentration of 100 mg mL-1. Cancer cells were found to be more sensitive than normal to the graphene composites, proving antitumor activity. The pro and antioxidant effects of the tested nanomaterials depend on the pH level. At physiological conditions, in the Fenton's system, all but RGO+Cu do not appear to be suitable as an implant nanomaterial. In the H2O2 oxidation system all materials present stable antioxidant effects; only ZnO+RGO+Cu is close to control prooxidant levels. When the nanomaterials are tested for oxidation by O2.- radicals, ZnO+RGO and Zn+RGO+Cu show prooxidant effects, as the prooxidant activity is kept for ZnO+RGO even at physiological acidity pH 7.4.Item Collagen/(ZnTiO3/SiO2) composites of an wide spectrum antimicrobial activity(2020-01-01) Vladkova T.; Staneva A.; Albu-Kaya M.; Martinov B.; Ivanova I.The aim of this study is to prepare collagen composites of an increased wide spectrum antimicrobial activity using zinc titanate embedded in a silane matrix (ZnTiO3 /SiO2). Aiming to improve the predictability between the patient outcome and the in vitro antimicrobial testing, four Gram-negative, two Gram-positive bacterial strains, two fungi and seven mixed cultures are used in this study. A higher antimicrobial activity of Collagen/(ZnTiO3/SiO2) composites as compared to that of Collagen/ZnTiO3 ones is found against all test mono-microbial strains. Collagen/(ZnTiO3 /SiO2) composites demonstrate also an well expressed action against the mixed test bacterial cultures, in the most cases a better one compared to that against the bacteria participating in the corresponding mixed bacterial cultures. The increased antimicrobial effect is due to a more homogeneous distribution of the submicron ZnTiO3 aggregates embedded in a silane matrix along the collagen fibrils and a formation of a specific, snail-like structure depicted by SEM. The specific activity against different microbial cells and mixed bacterial cultures is ascribed to features of the microbial cells: size, shape, cell membrane and walls as well as to different exopolymeric substances (EPSs) and their concurrent adsorption in cases of mixed bacterial cultures, as well as the EPSs concurrent adsorption being similar to the concurrent protein adsorption from blood plasma known as Vroman's effect. The wide spectrum high activity against fungi, mono-and multi-specie bacterial cultures makes the studied Collagen/(ZnTiO3 /SiO2) composites a promising antimicrobial biomaterial.Item Composition, synthesis and properties of color architecture building foam glass obtained from waste packing glass(2013-05-21) Lakov L.; Toncheva K.; Staneva A.; Ilcheva Z.; Simeonova T.The foam glass is known mainly as an insulation material. It is less popular for the production of industrial colored foam glass. This material is for the application as coatings for building, architectural and artistic elements, especially in interior design. The synthesized compositions contain different coloring and foaming components. New foaming agents are characterized with dual function, both for foaming and coloring. By present study some environmental problems are solved for utilization of waste glasses to obtain a color foam glasses for use as heat and sound insulation. The obtained results are a part of a more general project for the development of technologies and special equipment for production of foam glasses.Item Composition, synthesis and properties of insulation foam glass obtained from packing glass waste(2013-05-21) Lakov L.; Toncheva K.; Staneva A.; Simeonova T.; Ilcheva Z.So far, the starting compositions for obtaining foam glass have been developed based on glasses pre-synthesized for the purpose. From the point of view of such important issues as increasing the energy efficiency and utilization of municipal and industrial waste, the possibility for production of foam glass insulation out of packing glass waste is a very good alternative. The present study to suggest a decision for utilization of waste glass and serves as a basis for developing the technology for production of continuous strip of foam glass material. This technology will be implemented in vertical production installation, which is currently under construction.Item Determination of the sensing characteristics of SiO2-Bi2O3-TiO2 system towards relative humidity(2018-01-01) Afify A.S.; Slavov S.S.; Mahmoud A.E.R.; Hassan M.; Ataalla M.; Staneva A.; Mohamed A.The aim of the present study is to determine the relative humidity (RH) sensing characteristics of the glass and glasscrystalline materials based on SiO2-Bi2O3-TiO2 system prepared by the melt quenching and controlled glass crystallization methods. Sensors were obtained by screen-printing of the prepared compositions onto alumina substrates with Pt electrodes. The sensors were tested in the range (0.0 - 96%) of the relative humidity at room temperature. The results have shown that most of the obtained glass ceramic materials had a lower sensitivity towards RH. The composition 20SiO2.30Bi2O3.50TiO2 has possessed the highest permittivity value (3000 F.m-1) and the lowest value of dielectric loss (0.0002) at room temperature which make it a promising candidate for some industrial applications such as energy storage, electronic capacitors as well as memory devices.Item DIELECTRIC PROPERTIES OF NEW COMPOSITES BASED ON GRAPHENE OXIDE AND NANO-SIZED ZnO(2021-01-01) Staneva A.; Martinov B.; Slavov S.; Karashanova D.; Mateeva J.; Melo B.M.G.; Costa L.C.The objectives of this study were to obtain a complete series of graphene oxide and nano sized zinc oxide and to make a structural and phase characterization of the resulting composites. XRD, SEM, EDX, TEM and impedance analyses were used to investigate these materials as energy storage devices. The complex dielectric permittivity was measured for all samples as a function of frequency. All dielectric characteristics were studied (frequencies from from 100 Hz to 1 MHz and temperatures from 150 to 400 K). The composite GO/ZnO - 80/20 is closer to the desired properties.Item EFFECT OF GRAPHENE OXIDE AND REDUSED GRAPHENE OXIDE ON ELECTRICAL PROPERTIES OF YBCO AND YBCO/Ag COMPOSITES(2020-01-01) Staneva A.; Mateeva J.; Martinov B.; Blagoev B.; Nurgaliev T.Series of bulk composites based on YBCO superconductors, silver and graphene oxide/reduced graphene oxide are synthesized. The aim of this study is to determine the effect of GO and RGO on the superconducting properties of YBCO composites. Series of YBCO and YBCO/Ag phases are synthesized by the ceramic method. GO and RGO are obtained by the modified Hammer’s method. Series of YBCO, YBCO/Ag composites with GO or RGO are studied. The temperatures of the superconducting transition of the obtained composites are determined and the effect of GO/ RGO is investigatedItem Electric properties of new composite materials based on RGO, nanosized ZnO and Cu nanoparticles(2021-02-16) Martinov B.; Slavov S.; Staneva A.; Dimitrov D.; Mateeva J.Graphene nanostructures combine properties that make them an attractive material for various technical applications. The objective of this study is to obtain a series composites based on Reduced graphene oxide (RGO), nano-sized ZnO and Cu nanoparticles. RGO is synthesized by a modified Hammer's method and chemical reduction after sonication. ZnO nanoparticles are obtained by the Sol-Gel method. The composites' phases and structures are characterized by XRD, SEM, TEM, and EDX analysis. It is shown that ZnO is monophasic with a particle size of 48 nm. A series of composite materials based on RGO, ZnO and Cu nanoparticles is obtained by ultrasonic treatment. Electrical and dielectric properties are measured by Impedance analyser and RLC bridge. For comparison, the conductivity for 100% RGO is 309.513 S/m and for 100 % Cu nanosized is 0.0056 S/m. Therefore, it should be initially concluded that increasing the RGO in the mixture will increase the conductivity, and increasing nanosized Cu will decrease it. The presence of cluster regions in the composites with different conductivity is found: 1) nano grains of conductive copper which are partially or completely surrounded by 2) low-conductivity shells of copper oxide and a minimal number of RGO sheets. The present work shows promising results for future research for the creation of new composite materials with controlled shape and size of copper oxide - RGO clusters. Dielectric measurements for RGO/ZnO composites are made in range from 5 mass% to 100 mass% content of RGO, the composites show variable conductivity. For lower concentration of RGO, selected samples are dielectrics.Item Exploring the impact of different soft reducers in Reduced Graphene Oxide synthesis(2019-01-01) Kichukova D.; Staneva A.; Kovacheva D.; Tzoneva I.The most common way for the synthesis of bulk graphene is based on exfoliation of graphite. This method involves oxidation of graphite using highly oxidizing agents and subsequently reducing graphene oxide (GO) to graphene. Reduced graphene oxide (RGO) is prepared from reduction of GO by thermal, chemical or electrical treatments. Different reducing agents are widely used for the chemical reduction. However, many of the commonly used reducing agents are hazardous. To decrease the level of toxicity, ``green`` materials recently were applied. The present study reports the preparation of RGO with the use of mild and nontoxic reducing agents. The obtained materials were characterized by X-Ray powder diffraction, Raman and FTIR spectroscopy, as well as by SEM and TEM electron mycroscopy. The results show that at the conditions choosen for the experiment glycerol, ethylene glycol and citric acid do not reduce GO. The use of succrose, acetic acid and oxalic acid in the rection process resulted in an incomplete reduction of GO, The use of urea, L-ascorbic acid and glycine leaded to the removal of interlayer functional groups in GO where the complete reduction of GO is acheaved in the case of the use of L-ascorbic acid and glycine. The results show that L-ascorbic acid and glycine reduce graphene oxide effectively but, depending on the type of the reducer, the morphological properties of the obtained RGO are different.Item Facile Synthesized Cu–RGO and Ag–RGO Nanocomposites with Potential Biomedical Applications(2022-06-01) Kichukova D.; Spassova I.; Kostadinova A.; Staneva A.; Kovacheva D.In the present study, we report on the facile prepared nanocomposites of reduced graphene oxide RGO with Cu and Ag. The synthesis was performed through an environmentally friendly and easy method by simultaneous reduction in solutions containing Cu2+ or Ag+ and graphene oxide (GO) using zinc powder as a reducing agent in aqueous acidic media. The composites are characterized by powder X-ray diffraction, low-temperature nitrogen adsorption, X-ray photoelectron and FTIR and Raman spectroscopies, as well as Scanning and Transmission electron microscopies. The antibacterial activity of the composites was tested for Staphylococcus aureus, Escherichia coli and antifungal activity for Candida albicans. The cytotoxicity of the materials was studied towards two types of eukaryotic cells—MDCK II and A549 cell lines. The composites obtained consist of homogeneously distributed Cu and Ag nanoparticles on the surface of graphene sheets and manifest good antimicrobial activity and high cytotoxicity. The results clearly show that both metal–RGO composites can be successfully used as antimicrobial and anticancer agents.Item Glass formation and structure of glasses in the ZnO-WO3-La2O3-Al2O3 system(2015-01-01) Ataalla M.; Milanova M.; Aleksandrov L.; Iordanova R.; Staneva A.; Dimitriev Y.The glass formation region in the section 90(xZnO.yWO3.zLa2O3).10Al2O3 of a constant Al2O3 content of 10 mol % and varying amounts of WO3, ZnO and Nd2O3 from ZnO-WO3-La2O3-Al2O3 system is determined by the melt quenching technique (with cooling rates of 10 Ks-1 - 102 Ks-1). The glasses are obtained from compositions of a high WO3 content (60 mol % - 75 mol %). The amorphous state of the samples is verified by X-ray diffraction (XRD). The thermal parameters of the investigated glasses are obtained by differential thermal analysis (DTA). The glass transition temperature (Tx) is in the range 440°C - 510°C, while the crystallization temperature (Tg) varies from 520°C to 650°C. The glasses are characterized by a good thermal stability in respect to crystallization. ΔT varies in the range of 60°C - 135°C (ΔT = Tx-Tg). The glasses structure is studied by IR spectroscopy. It is established that the amorphous network is built up mainly by WO6 octahedra connected through W-O-W bridges.Item Modeling of the thermo physical parameters of material in the foaming zone in equipment for continuous band of foam glass(2015-01-01) Toncheva K.; Staneva A.Modeling of the thermo physical properties of the material in the foaming zone of an installation for continuous band of foam glass manufacture is presented. The initial physical assumptions concerning the implementation of the process are pointed out. The changes of properties like density, thermal conductivity, and specific heat capacity of the foamed material, i.e. a mixture of glass powder and foamers are followed in the course of the heating process.Item Phase formation and microstructure in Re1-xCax Ba2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics(2006-03-01) Stoyanova-Ivanova A.; Terzieva S.; Staneva A.; Mikli V.; Traksmaa R.; Dimitriev Y.; Kovachev V.We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-xCax Ba2Cu3O7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.Item Phase formation and microstructure in Re1-xCax Ba2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics(2006-03-01) Stoyanova-Ivanova A.; Terzieva S.; Staneva A.; Mikli V.; Traksmaa R.; Dimitriev Y.; Kovachev V.We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-xCax Ba2Cu3O7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.Item Preparation and antimicrobial activity of collagen/(RGO/ZnO/TiO2/SiO2) composites(2020-01-01) Staneva A.; Albu-Kaya M.; Martinov B.; Ivanova I.; Vladkova T.A serial investigation is initiated aiming to explore the biological activity of some newly synthetized chemical compounds for the development of novel antimicrobial collagen based biomaterials. Collagen/ZnTiO3, Collagen/RGO, Collagen/(Ag/RGO), Collagen/(Ag/RGO/SiO2) and Collagen/(ZnTiO3/SiO2) composites have been so far studied and all of them demonstrate a specific antimicrobial activity against Gram-negative and Gram-positive bacteria and in some cases against fungi. The aim of this investigation is to develop new antimicrobial collagen biomaterials using RGO, ZnO, and TiO2 embedded in TEOS as another antimicrobial agent, combining the biological activity of RGO, ZnO and TiO2 with the dispersing effect of SiO2. The new Collagen/(RGO/ZnO/TiO2/SiO2) composites demonstrate an antimicrobial activity dependent on the agent loading level. It is specific in respect to Gram-negative, Grampositive bacteria and fungi. An optimal balance between the antimicrobial activity and the cytotoxicity is achieved by varying the concentration of the antimicrobial agent, RGO/ZnO/TiO2/SiO2, in Collagen/(RGO/ZnO/TiO2/SiO2) composites. It is suggested that the mechanism of the antimicrobial action includes the simultaneous proceeding of (i) metal ions chelation; (ii) free oxygen radicals formation due to the interactions between the microbial cells and the antimicrobial agent; (iii) mechanical demolition of the cell walls and membranes by RGO crystal nanoparticles. The broad spectrum antibacterial and anti-fungal activity combined with the low cytotoxicity at an optimal Collagen/ Antimicrobial agent ratio makes the studied Collagen/(RGO/ZnO/TiO2/SiO2) composites a promising antimicrobial material increasing the medical biomaterials assortment. © 2020 by the authors.Item Preparation and characterization of a zinc oxide nanopowder supported onto inorganic clay(2016-01-01) Hassan M.; Afify A.S.; Ataalla M.; Mohammed A.; Staneva A.; Dimitriev Y.; Tulliani J.M.Zinc oxide nanoparticles are obtained by a wet chemical method using zinc sulphate as a raw material. Doping sepiolite, micro-fibrous inorganic clay, with ZnO after precipitation under basic conditions and subsequent thermal treatment is investigated as both materials are abundant. They are used for the development of humidity and gas sensors of great environmental importance. The particle size distribution, the morphology and the composition of the powder samples are characterized by X-Ray diffraction accompanied by Field Emission Scanning Electron Microscopy and High Resolution-Transmission Electron Microscopy techniques. The data obtained confirm the formation of zinc oxide nanoparticles of a size of 10 nm on the modified sepiolite grains.Item Recent Progress in Antioxidant Active Substances from Marine Biota(2022-03-01) Vladkova T.; Georgieva N.; Staneva A.; Gospodinova D.Background: The well-recognized but not fully explored antioxidant activity of marinebiota-derived, biologically active substances has led to interest in their study as substitutes of antibiotics, antiaging agents, anticancer and antiviral drugs, and others. The aim of this review is to present the current state of the art of marine-biota-derived antioxidants to give some ideas for potential industrial applications. Methods: This review is an update for the last 5 years on the marine sources of natural antioxidants, different classes antioxidant compounds, and current derivation biotechnologies. Results: New marine sources of antioxidants, including byproducts and wastes, are presented, along with new antioxidant substances and derivation approaches. Conclusions: The interest in high-value antioxidants from marine biota continues. Natural substances combining antioxidant and antimicrobial action are of particular interest because of the increasing microbial resistance to antibiotic treatments. New antioxidant substances are discovered, along with those extracted from marine biota collected in other locations. Byproducts and wastes provide a valuable source of antioxidant substances. The application of optimized non-conventional derivation approaches is expected to allow the intensification of the production and improvement in the quality of the derived substances. The ability to obtain safe, high-value products is of key importance for potential industrialization.Item Synthesis and characterization of glass doped reduced graphene oxide(2015-01-01) Shalaby A.; Aleksandrov L.; Iordanova R.; Staneva A.; Dimitriev Y.Graphene is very attractive material which has high conductivity and good electrical properties. By using glass as a matrix to incorporate the graphene, it is possible to improve the conductivity and the electrical properties of the glass. In our previous study we synthesized composite material by adding of reduced graphene oxide (RGO) to silica. In this work we continue our experiments to synthesize a composite material on a glass basis in the PbO-ZnO-B2O3 system. The differential thermal analysis of the present glass showed that the glass transition temperature (Tg) is situated at ca 415°C. The synthesized glass was doped with 20 % of reduced graphene oxide (RGO). A mixture of glass with RGO was heated at different temperature values for different time taking into consideration the glass transition temperature. The characterization is performed by X-ray phase analysis, DTA and SEM analysis. It was found according to the XRD results that graphene was kept inside the glass matrix till 600°C.Item Synthesis and characterization of ybco and ybco/ag superconducting ceramic composites containing reduced graphene oxide(2019-01-01) Mateeva J.; Staneva A.; Martinov B.; Blagoev B.; Nurgaliev T.The high-temperature ceramic superconductors and nanomaterials are among the most promising groups of materials that are intensively studied. Graphene is a new material with unique electrical, optical and biological properties. The high mobility of graphene charges implies the possibility of using it as a suitable additive improving the superconductors' physical characteristics. The idea of this study is to synthesize series of bulk composites based on YBCO superconductors, silver and RGO with superconducting properties. The YBCO phase is obtained by a ceramic technology. It includes Ag aiming better sintering. Graphene is synthesized by a modified Hammer's method. XRD is applied to verify the obtaining of the starting phases. The synthesized composites are characterized by XRD, SEM and EDX analysis. All composites prepared are superconductive and have a Meissner effect.