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    ELECTROCHEMICAL BEHAVIOR OF THE ANTINEOPLASTIC AGENT ETOPOSIDE AT A GRAPHENE-BASED MODIFIED ELECTRODE: ITS SQUARE-WAVE ADSORPTIVE STRIPPING VOLTAMMETRIC DETERMINATION IN THE PHARMACEUTICAL FORMULATIONS
    (Editura Acad Romane, 2018) Talay Pinar, Pinar; Saka, Cafer; Yardim, Yavuz
    An electrochemical sensor based on the graphene (GR) was prepared, and used for the determination of etoposide (ETO). The electrochemical behaviors of this compound on GR modified glassy carbon electrode (GR/GCE) were investigated by cyclic voltammetry and square-wave adsorptive stripping voltammetry (SWAdSV). Using SWAdSV, a linear calibration curve was obtained for ETO determination in 0.1 M Britton-Robinson (BR, pH 4.0) buffer solution at +0.56 V (vs. Ag/AgCl) (after 30 s accumulation at 0.1 V). A linear relationship was found between peak currents and the concentration of ETO within 0.025 to 0.5 mu g mL(-1), with a detection limit of 0.0023 mu g mL(-1). The developed method was successfully applied to the determination of ETO in the pharmaceutical formulations with good recoveries.
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    Electrochemical behavior of the antineoplastic agent etoposide at a graphene-based modified electrode: Its square-wave adsorptive stripping voltammetric determination in the pharmaceutical formulations
    (Editura Academiei Romane, 2018) Pinar, Pinar Talay; Saka, Cafer; Yardim, Yavuz
    An electrochemical sensor based on the graphene (GR) was prepared, and used for the determination of etoposide (ETO). The electrochemical behaviors of this compound on GR modified glassy carbon electrode (GR/GCE) were investigated by cyclic voltammetry and square-wave adsorptive stripping voltammetry (SWAdSV). Using SWAdSV, a linear calibration curve was obtained for ETO determination in 0.1 M Britton-Robinson (BR, pH 4.0) buffer solution at +0.56 V (vs. Ag/AgCl) (after 30 s accumulation at 0.1 V). A linear relationship was found between peak currents and the concentration of ETO within 0.025 to 0.5 ?g mL -1 , with a detection limit of 0.0023 ?g mL -1 . The developed method was successfully applied to the determination of ETO in the pharmaceutical formulations with good recoveries. © Editura Academiei Romane. All rights reserved.
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    Enhanced electrochemical double-layer capacitive performance with CO2 plasma treatment on activated carbon prepared from pyrolysis of pistachio shells
    (Pergamon-Elsevier Science Ltd, 2020) Sahin, Omer; Yardim, Yavuz; Baytar, Orhan; Saka, Cafer
    This study reports an original approach based on the CO2 plasma treatment on modification of the chemical or physical properties of activated carbon(AC) from the pistachio shells as a waste for application as electrochemical double-layer capacitors(EDLC). In the AC production experiments, impregnation ratio, impregnation pre-treatment temperature, activation temperature and activation time are investigated. In the AC modification experiments with plasma treatment, the effects of plasma gases, plasma power and plasma time are performed. The results of the different conditions indicated that the structural properties of the obtained AC were significantly dependent on the plasma and pyrolysis parameters. The surface properties of the raw AC and plasma-treated AC (PTAC) with X-ray photoelectron spectroscopy (XPS), nitrogen adsorption technique, and scanning electron microscope (SEM) are characterized. Surface area values for the raw AC and PTAC are 768 and 1250 m(2) g(-1), respectively. A change in the peak positions and an increase in the percentage of oxygen of the AC treated with CO2 plasma were obtained from XPS results. After 15 min of CO2 plasma activation, a significant increase in the capacitance of up to about 141% was obtained as a 118.4 F g(-1) compared to 49.98 F g(-1) for untreated AC. The results show that the plasma treatment on the specific surface area and surface functional groups of AC has a significant impact. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Improvement of electrochemical double-layer capacitance by fast and clean oxygen plasma treatment on activated carbon as the electrode material from walnut shells
    (Pergamon-Elsevier Science Ltd, 2020) Saka, Cafer; Baytar, Orhan; Yardim, Yavuz; Sahin, Omer
    In this study, a simple, fast, and clean oxygen plasma method is presented to increase the surface area of activated carbon from walnut shells (WAC) and to connect functional groups containing oxygen to the carbon sample surface. X-ray photoelectron spectroscopy (XPS), nitrogen adsorption technique, Fourier-transform infrared spectroscopy (FTIR), X-Ray Diffraction (XRD), and scanning electron microscope (SEM) analyses to investigate the properties of the WAC and WACP are performed. Cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS) measurements are used to investigate the capacitance properties of the supercapacitors. A significant increase in the surface area of the WAC was increased from 22 m(2) g(-1) to 78 m2 g(-1) after oxygen plasma treatment. The specific capacitance was improved from 6.98 F g(-1) to 76.89 F g(-1) at 2.5 mV s(-1). The devices with functionalized electrodes exhibited cyclic stability of 78% after 5000 cycles.
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    Iodine adsorption and electrochemical double-layer capacitor characteristics of activated carbon prepared from low-cost biomass
    (Taylor & Francis Inc, 2023) Saka, Cafer; Yardim, Yavuz; Sahin, Omer; Baytar, Orhan
    The efficient adsorption application and electric double-layer capacitor material with low-cost biomass-based activated carbon materials have been quite common recently. In this study, chestnut shell-based activated carbons were produced by chemical activation. ZnCl2, H3PO4, and KOH agents were used for chemical activation. The obtained activated carbon, iodine adsorption from aqueous solutions, and its use as an electro capacitor were investigated. The scanning electron microscope, nitrogen adsorption/desorption, and Fourier transform infrared spectroscopy were used for characterization. The values of surface area and iodine adsorption capacity of the chestnut shell-based activated carbon are 1544 m(2) g(-1) and 1525 mg g(-1). As a result, a specific capacitance of 97 Fg(-1) with chestnut shell-based activated carbon was obtained in a 1 M KCl electrolyte for the electrochemical double-layer capacitor. This study shows that activated carbon based on the chestnut shell can be used both as an electrochemical energy storage material and as an adsorbent in iodine adsorption.
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    Oxygen and nitrogen-doped carbon particles derived from pyrolysis of Chlorella vulgaris and Spirulina platensis microalgae as an efficient electrode material for supercapacitor application
    (Taylor & Francis Inc, 2023) Yardim, Yavuz; Saka, Cafer
    This study consists of the thermal activation of Chlorella vulgaris and Spirulina platensis microalgae with a potassium hydroxide (KOH) chemical agent in a carbon dioxide (CO2) atmosphere and the formation of nitrogen and oxygen-doped material from the hydrothermal interaction of the obtained activated carbons with nitric acid. The obtained nitrogen and oxygen-doped activated carbons were used in the production of electrochemical super capacitors. The morphological properties of the obtained pores were evaluated by transmission electron microscopy (TEM). Electrochemical properties were evaluated according to the cyclic voltammetry (CV) method in sulphuric acid (H2SO4), potassium chloride (KCl), and sodium hydroxide (NaOH) electrolytes with a scanning rate in the range of 2.5-50 mVs(-1). Nitrogen and oxygen doped electrode electrochemical capacitor based on Spirulina platensis microalgae showed the highest specific capacitance of 99.53 Fg(-1) at a scanning rate of 2.5 mV s(-1) in 1 M H2SO4 electrolyte. In contrast, the supercapacitor based on an activated carbon electrode from Chlorella vulgaris microalgae showed the highest specific capacitance of 156.04 Fg(-1) at a scan rate of 2.5 mV s(-1) in 1 M KCl electrolyte.