Browsing by Author "Pashova K."

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    COMPARATIVE STUDY OF POLYPHENOLIC COMPOSITION AND REDUCING PROPERTIES OF EXTRACTS OF CANNABIS SATIVA L., CANNABIS INDICA AND CANNABIS HYBRID
    (2024-01-01) Vetskov N.; Kaloyanov N.; Hinkov I.; Diankov S.; Pashova K.; Gerasimova V.; Funeva-Peycheva M.; Yankovska-Stefanova T.; Garbev A.
    Cannabis Sativa L., Cannabis Indica and Cannabis Hybrid are widespread plant species that find legal use in many countries around the world. The first of them has found considerable application in medicine, cosmetics, building construction, textile and food industries. Cannabis Indica and Cannabis Hybrid are used as raw materials for the extraction of oils that are used as pain relievers as well as for recreation purposes. The aim of the present study is to compare the polyphenolic composition of extracts from the three types of plants, by the maceration method of dry green leaf mass consisting of inflorescences and leaves. Ethanol (99.9 %) is used as an extractant, and the duration of the maceration process is seven days, at room temperature and stirring. The polyphenol composition is determined using HPLC-DAD method. The following polyphenol composition is found in extracts of Cannabis Sativa L.: epigallocatechin, rutin, myricetin, quercetin and kaempferol. On the other hand, quercetin and kaempferol are detected in the Cannabis Indica samples, while epigallocatechin, quercetin and kaempferol are present in the hybrid sort. In addition, green synthesis of silver nanoparticles by using sunlight or microwave irradiation was carried out to evaluate the reduction properties of three cannabis extracts. The least quantity of silver nanoparticles was obtained in the presence of Cannabis Sativa L. extracts. From the other two species of cannabis, microwave irradiation produces more silver nanoparticles, with smaller sizes, while exposure to direct sunlight produces fewer particles, but with larger sizes.
  • No Thumbnail Available
    Item
    Erratum: Computer-aided design of graphene and 2D materials synthesis via magnetic inductive heating of 11 transition metals (J. Phys. D: Appl. Phys. (2021) 55 (105302) DOI: 10.1088/1361-6463/ac357d)
    (2022-04-14) Dhaouadi E.; Hinkov I.; Pashova K.; Challab N.; Roussigné Y.; Abderrabba M.; Farhat S.
    There was a typo during the production of our paper. The alpha factor has been omitted from equation (3). The equation should appear as follows: ρ = ρ0 (1 + αT).
  • No Thumbnail Available
    Item
    Graphene synthesis by inductively heated copper foils: Reactor design and operation
    (2020-04-01) Pashova K.; Dhaouadi E.; Hinkov I.; Brinza O.; Roussigné Y.; Abderrabba M.; Farhat S.
    We report on the design of a reactor to grow graphene via inductively heating of copper foils by radio frequency (RF) magnetic fields. A nearly uniform magnetic field induced by Helmholtz-like coils penetrates the copper foil generating eddy currents. While the frequency of the current is being rapidly varied, the substrate temperature increases from room temperature to ~1050 °C in 60 s. This temperature is maintained under Ar/H2 flow to reduce the copper, and under Ar/H2/CH4 to nucleate and grow the graphene over the entire copper foil. After the power cut-off, the temperature decreases rapidly to room temperature, stopping graphene secondary nucleation. Good quality graphene was obtained and transferred onto silicon, and coated with a 300 nm layer of SiO2 by chemical etching of the copper foil. After synthesis, samples were characterized by Raman spectroscopy. The design of the coils and the total power requirements for the graphene induction heating system were first estimated. Then, the effect of the process parameters on the temperature distribution in the copper foil was performed by solving the transient and steady-state coupled electromagnetic and thermal problem in the 2D domain. The quantitative effects of these process parameters were investigated, and the optimization analysis results are reported providing a root toward a scalable process for large-sized graphene.
  • No Thumbnail Available
    Item
    Graphene synthesis by microwave plasma chemical vapor deposition: Analysis of the emission spectra and modeling
    (2019-04-03) Pashova K.; Hinkov I.; Aubert X.; Prasanna S.; Bénédic F.; Farhat S.
    In this article, we report on some of the fundamental chemical and physical processes responsible for the deposition of graphene by microwave plasma-enhanced chemical vapor deposition. The graphene is grown by plasma decomposition of a methane and hydrogen mixture (CH4/H2) at moderate pressures over polycrystalline metal catalysts. Different conditions obtained by varying the plasma power (300-400 W), total pressure (10-25 mbar), substrate temperature (700 °C-1000 °C), methane flow rate (1-10 sccm) and catalyst nature (Co-Cu) were experimentally analyzed using the in situ optical emission spectroscopy technique to assess the species rotational temperature of the plasma and the H-atom relative concentration. Then, two modeling approaches were developed to analyze the plasma environment during graphene growth. As a first approximation, the plasma is described by spatially averaged bulk properties, and the species compositions are determined using kinetic rates in the transient zero-dimensional (0D) configuration. The advantage of this approach lies in its small computational demands, which enable rapid evaluation of the effects of reactor conditions and permit the identification of dominant reactions and key species during graphene growth. This approach is useful for identifying the relevant set of species and reactions to consider in a higher-dimensional model. The reduced chemical scheme was then used within the self-consistent two-dimensional model (2D) to determine auto-coherently the electromagnetic field, gas and electron temperatures, heavy species, and electron and ion density distributions in the reactor. The 0D and 2D models are validated by comparison with experimental data obtained from atomic and molecular emission spectra.