Przeglądaj wg Autor "Guskos, Nikos"

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    PozycjaOpen Access
    DC magnetization of titania supported on reduced graphene oxide flakes
    (De Gruyter, 2021-10-19) Guskos, Nikos; Żołnierkiewicz, Grzegorz; Guskos, Aleksander; Aidinis, Konstantinos; Glenis, Spiros; Wanag, Agnieszka; Kusiak-Nejman, Ewelina; Narkiewicz, Urszula; Morawski, Antoni W.; Zachodniopomorski Uniwersytet Technologiczny w Szczecinie
    DC magnetization of a series of titania nano-composites modified with reduced graphene oxide (rGO) has been investigated. Hysteresis loops observed at room temperature disappeared at low temperatures. At a temperature of about 100 K, a phase transition to the super-ferromagnetic order state was observed, probably due to the linear expansion and self-reorientation of the magnetic moments. Processes associated with magnetic moment reorientation can cause a hysteresis loop to disappear at low temperatures as well as superferromagnetic ordering. It was suggested that the isolated nanoparticle in the nanopore could be used to create a "compass" at a nanometer-sized level that would be many times more sensitive than the conventional one. Measurements of the zero-field cooling and field cooling modes do not exclude the possibility of the coexistence of a superparamagnetic state.
  • Miniatura
    PozycjaOpen Access
    Magnetic moment centers in titanium dioxide photocatalysts loaded on reduced graphene oxide flakes
    (De Gruyter, 2021-01) Guskos, Nikos; Zolnierkiewicz, Grzegorz; Guskos, Aleksander; Aidinis, Konstantinos; Wanag, Agnieszka; Kusiak-Nejman, Ewelina; Narkiewicz, Urszula; Morawski, Antoni W.; Zachodniopomorski Uniwersytet Technologiczny w Szczecinie
    A whole series of titania nanocomposites modified with reduced graphene oxide (rGO) was prepared using solvothermal method followed by calcination. Modification of titania with rGO has been found to lead to better photocatalytic properties. The highest photocatalytic performance was obtained at calcination temperature of 600 degrees C. Electron paramagnetic resonance/ferromagnetic resonance measurements showed oxygen defects and ferromagnetic ordering systems. The linewidth of resonance line of oxygen defects decreased linearly with calcination temperature increasing up to 600 degrees C and an accompanying growth of mean crystallite size of anatase phase. The integrated resonance line intensity of oxygen defects depended on the calcination temperature and caused a very large increase in the intensity of resonance lines originating from oxygen defects, because inert atmosphere of calcination was enhanced by graphene presence. The occurrence of magnetic ordering system significantly influenced the performance of photocatalytic processes by changing the amount of oxygen defects.
  • Miniatura
    PozycjaOpen Access
    Magnetic Resonance Studies of Hybrid Nanocomposites Containing Nanocrystalline TiO2 and Graphene-Related Materials
    (MDPI, 2022-03-18) Guskos, Nikos; Żolnierkiewicz, Grzegorz; Kusiak-Nejman, Ewelina; Guskos, Aleksander; Aidinis, Konstantinos; Bobrowska, Marta; Berczynski, Paweł; Wanag, Agnieszka; Pełech, Iwona; Narkiewicz, Urszula; Morawski, Antoni W.; Zachodniopomorski Uniwersytet Technologiczny w Szczecinie
    Nanocomposites based on nanocrystalline titania modified with graphene related materials (reduced and oxidized form of graphene) showed the existence of magnetic agglomerates. All parameters of magnetic resonanc spectra strongly depended on the materials’ modification processes. The reduction of graphene oxide significantly increased the number of magnetic moments, which caused crucial changes in the reorientation and relaxation processes. At room temperature, a wide resonance line dominated for all nanocomposites studied and in some cases, a narrow resonance line derived from the conduction electrons. Some nanocomposites (samples of titania modified with graphene oxide, prepared with the addition of water or butan-1-ol) showed a single domain magnetic (ferromagnetic) arrangement, and others (samples of titania modified with reduced graphene oxide) exhibited magnetic anisotropy. In addition, the spectra of EPR from free radicals were observed for all samples at the temperature of 4 K. The magnetic resonance imaging methods enable the capturing of even a small number of localized magnetic moments, which significantly affects the physicochemical properties of the materials.