Browsing by Author "Radoykova T."
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Item Adsorption of Ag+ ions on hydrolyzed lignocellulosic materials based on willow, paulownia, wheat straw and maize stalks(2016-05-01) Vassileva P.; Radoykova T.; Detcheva A.; Avramova I.; Aleksieva K.; Nenkova S.; Valchev I.; Mehandjiev D.In the present work, the adsorption of Ag+ ions on hydrolyzed plant biomass (willow, paulownia, wheat straw and maize stalks) was investigated. Chemical analyses were performed to establish the composition of the obtained materials. Adsorption mechanism, adsorption sites and specific surface areas of these materials were examined by BET analysis, IR spectroscopy, XPS and EPR. The effects of contact time, acidity of initial solutions and Ag+ ion concentrations were followed. Pseudo-first-order, pseudo-second-order and intra-particle diffusion models were used to analyze kinetic data. In all cases, the adsorption was significantly affected by the pH value. Different types of adsorption isotherms of Ag+ ions (either Langmuir or Freundlich) were registered depending on the adsorbing material. The adsorption mechanism is complex, and the process passes through different stages as clustering of Ag+ ions and formation of elemental Ag. The maximal adsorption capacities varied from 2.05 to 6.07 mg g−1. The obtained results revealed that the examined waste lignocellulosic materials are promising adsorbents for Ag+ ions.Item Black liquor lignin products, isolation and characterization(2013-11-05) Radoykova T.; Nenkova S.; Valchev I.By extraction with toluene and ethyl acetate monomeric lignin compounds: 2-methoxyphenol, 2,6-dimethoxyphenol, 4-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-3,5-dimethoxybenzaldehyde, 1-(4-hydroxy-3-methoxyphenyl) ethanone, 1-(4-hydroxy-3,5-dimethoxyphenyl) ethanone, etc. were isolated from black liquor and sulfate lignin, and identified through GC/MS analysis. The identified low-molecular mass lignin compounds do not contain organic bonded sulphur. The sulfate lignin, separated from black liquor after acidification with acid was subjected to an alkaline treatment (4 h; 180oC; 5 % NaOH; lignin/NaOH ratio -1:8).Item Characterization of Bulgarian Copper Mine Tailing as a Precursor for Obtaining Geopolymers(2024-02-01) Ilieva D.; Angelova L.; Radoykova T.; Surleva A.; Chernev G.; Vizureanu P.; Burduhos-Nergis D.D.; Sandu A.V.Valorization of high-volume mine tailings could be achieved by the development of new geopolymers with a low CO2 footprint. Materials rich in aluminum and silicon with appropriate solubility in an alkaline medium can be used to obtain a geopolymer. This paper presents a study of copper mine tailings from Bulgaria as precursors for geopolymers. Particle size distribution, chemical and mineralogical composition, as well as alkaline reactivity, acidity and electroconductivity of aqueous slurry are studied. The heavy metal content and their mobility are studied by leaching tests. Sequential extraction was applied to determine the geochemical phase distribution of heavy metals. The studied samples were characterized by high alkalinity, which could favor the geopolymerization process. The water-soluble sulphates were less than 4%. The Si/Al ratio in mine tailing was found to be 3. The alkaline reactivity depended more so on the time of extraction than on the concentration of NaOH solution. The main part of the heavy metals was found in the residual fraction; hence, in high alkaline medium during the geopolymerization process, they will stay fixed. Thus, the obtained geopolymers could be expected to exert low environmental impact. The presented results revealed that studied copper mine tailing is a suitable precursor for geopolymerization.Item OBTAINING OF BALSAMIC POPLAR EXTRACT AS BIOSTIMULANT FOR AGRICULTURAL PLANTS(2024-01-01) Mechshanova A.; Polyakov V.; Surleva A.; Radoykova T.Modern varieties of agricultural plants have reached the limits of natural genetic variability in a few key parameters, and a further significant increase in their productivity and stress resistance using traditional approaches is extremely difficult. The use of biostimulants of various nature is considered as a promising way of sustainable development, allowing to increase yields without harmful effects on the environment. Plants are a source of a wide variety of biologically active substances (BAS), such as vitamins, alkaloids, glycosides, saponins, tannins, polysaccharides (gums, mucus, pectins, inulin, fibre, starch), flavonoids, resins, essential and fatty oils, organic acids, phytoncides, pigments and others. An important argument in favour of obtaining biologically active substances from poplar is the environmental friendliness of such a solution, since a lot of unused waste (bark, branches, wood) is generated during the logging process. The purpose of this study is to find the optimal extraction conditions and to investigate the influence of balsamic poplar extract on the change in physiological and biological parameters, as well as the productivity of soybean, cucumber, and sugar beet seeds. The qualitative composition of extracts from buds, twigs, catkins, and poplar wood processing waste has been determined. Among these extracts, the one from poplar wood processing waste is the most promising for further study due to its high content of flavonoids, tannins, saponins, amino acids, and polysaccharides. The optimal technological parameters for extracting these compounds have been identified, including the degree of grinding of the raw materials, the ratio of raw materials to extractant, the duration of extraction, and the concentration of the extractant. It has been found that the best extraction of flavonoids occurs when the raw materials are ground to a size of up to 15 mm and mixed with a ratio of 1:15 of raw materials to extractant for 36 hours using 96 % ethanol. The aftereffect of the application of the extract was traced in the ontogenesis of plants on the change in important physiological processes that influenced the productivity of products and their quality.Item Slag-based materials as catalysts in oxidation reactions(2014-01-01) Mihajlova I.; Radoykova T.; Ivanov G.; Stoyanova D.; Mehandjiev D.The ability to create new active catalysts for complete oxidation of carbon monoxide and organic compounds on the basis of the metallurgical slag for waste gas purification was proven. The procedure for the synthesis of the catalysts includes only acid and thermal activation of the metallurgical slag, during which in addition to increasing the catalytic activity, the specific surface area is also increased several times. ICP-OES analysis, Differential thermal analysis (DTA), Thermogravimetric analysis (TGA), X-ray diffraction (XRD) measurements and Fourier transform infrared (FTIR) spec-troscopy have been used for the study of the composition and structure of the resulting materials, and the processes of phase formation. The textural properties and the chemical composition of the surface have been investigated by Scanning electron microscopy (SEM), BET analysis and X-ray photoelectron spectroscopy (XPS). The catalysts obtainedfrom metal-lurgical slag can be successfully used for purification of waste gases in industry and transport.Item THE STUDY OF THE NATURAL SUBSTANCES OBTAINED FROM THE POPLAR BUDS AND THEIR USE FOR PROTECTION AGAINST THE ACTION OF IONIZING RADIATION(2023-06-30) Mechshanova A.; Polyakov V.; Radoykova T.Currently, natural plant extracts, which include biologically active substances, are increasingly used to produce medicines and cosmetics. In connection with the dangers of a radioecological crisis, special attention is paid to finding ways to protect against the effects of chronic exposure to low-intensity ionizing radiation in natural conditions. Currently, there is no ideal and safe radioprotective agent available, and we are seeing a great effort to find these agents from natural sources. Poplar extract is possible for use as a radioprotective shield from γ-radiation. Samples of protective screens were made from poplar extract on paper and showed a significant radioprotective effect. Phenolic compounds and flavonoids are widely present in plants as a second metabolite and are considered for research depending on their benefits for human health, healing and preventing many disorders. The main biologically active properties of flavonoids include antioxi-dant, anti-inflammatory, antitumor, rejuvenating, antibacterial and viral, neuroprotective and radioprotective action. The aim of this work was – the study of Flavonoids in an extract obtained from poplar buds and the possibility of their use for protection against radiation. Materials and methods. The object of research is the vegetative organs of poplar (buds). In the process of work, experimental studies were carried out on the extraction and separation of natural compounds, identification of flavonoids, and study of the chemical composition of biologically active complexes of poplar and preparations based on them. Research results. Data from these studies provide the identification of flavonoids by spectroscopy and quantification of flavonoids in poplar bud extract and can contribute to the optimization of radioprotection procedures. The main components found in the poplar buds dry extract are 2’,6’-dihydroxy-4’-methoxychalcone – are 2’,6’-dihydroxy-4’-methoxy-chalcone – 2.67 %, 3,4-dihydro-2’,6’-dihydroxy-4’-methoxychalcone – 2.33 %, pinobaxin – 1.91 %, chrysin – 0.76 %, pinostrobin – 0.04 %, pinocembrin – 0.61 %, tectochrysin – 0.54 % and galangin – 0.18 % of dry material. The results showed that the power of the penetrating radiation decreases with increasing the thickness of the protective screen. The power of penetrating radiation decreased from 78 % at the layer of 0.5 mm to 10 % at 3 mm layer thickness. Further increasing the thickness of the protective screen (>3 mm), doesn’t affect the dose rate. Conclusions. The composition of the poplar buds’ ethanol extract was investigated. Samples of protective screens made on the basis of poplar extract on paper showed a significant radioprotective effect on low-intensity ionizing radiation.Item Utilization Perspectives of Lignin Biochar from Industrial Biomass Residue(2023-06-01) Naydenova I.; Radoykova T.; Petrova T.; Sandov O.; Valchev I.The present study aimed at utilizing technically hydrolyzed lignin (THL), industrial biomass residue, derived in high-temperature diluted sulfuric acid hydrolysis of softwood and hardwood chips to sugars. The THL was carbonized in a horizontal tube furnace at atmospheric pressure, in inert atmosphere and at three different temperatures (500, 600, and 700 °C). Biochar chemical composition was investigated along with its HHV, thermal stability (thermogravimetric analysis), and textural properties. Surface area and pore volume were measured with nitrogen physisorption analysis often named upon Brunauer–Emmett–Teller (BET). Increasing the carbonization temperature reduced volatile organic compounds (40 ÷ 96 wt. %), increased fixed carbon (2.11 to 3.68 times the wt. % of fixed carbon in THL), ash, and C-content. Moreover, H and O were reduced, while N- and S-content were below the detection limit. This suggested biochar application as solid biofuel. The biochar Fourier-transform infrared (FTIR) spectra revealed that the functional groups were gradually lost, thus forming materials having merely polycyclic aromatic structures and high condensation rate. The biochar obtained at 600 and 700 °C proved having properties typical for microporous adsorbents, suitable for selective adsorption purposes. Based on the latest observations, another biochar application was proposed—as a catalyst.Item Utilization Perspectives of Lignin Biochar from Industrial Biomass Residue(2023-06-01) Naydenova I.; Radoykova T.; Petrova T.; Sandov O.; Valchev I.The present study aimed at utilizing technically hydrolyzed lignin (THL), industrial biomass residue, derived in high-temperature diluted sulfuric acid hydrolysis of softwood and hardwood chips to sugars. The THL was carbonized in a horizontal tube furnace at atmospheric pressure, in inert atmosphere and at three different temperatures (500, 600, and 700 °C). Biochar chemical composition was investigated along with its HHV, thermal stability (thermogravimetric analysis), and textural properties. Surface area and pore volume were measured with nitrogen physisorption analysis often named upon Brunauer–Emmett–Teller (BET). Increasing the carbonization temperature reduced volatile organic compounds (40 ÷ 96 wt. %), increased fixed carbon (2.11 to 3.68 times the wt. % of fixed carbon in THL), ash, and C-content. Moreover, H and O were reduced, while N- and S-content were below the detection limit. This suggested biochar application as solid biofuel. The biochar Fourier-transform infrared (FTIR) spectra revealed that the functional groups were gradually lost, thus forming materials having merely polycyclic aromatic structures and high condensation rate. The biochar obtained at 600 and 700 °C proved having properties typical for microporous adsorbents, suitable for selective adsorption purposes. Based on the latest observations, another biochar application was proposed—as a catalyst.