Yazar "Gulce, Ahmet" seçeneğine göre listele

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    Amperometric biosensors based on deposition of gold and platinum nanoparticles on polyvinylferrocene modified electrode for xanthine detection
    (ELSEVIER, 2011) Bas, Salih Zeki; Gulce, Handan; Yildiz, Salih; Gulce, Ahmet
    In this study, new xanthine biosensors, XO/Au/PVF/Pt and XO/Pt/PVF/Pt, based on electroless deposition of gold(Au) and platinum(Pt) nanoparticles on polyvinylferrocene(PVF) coated Pt electrode for detection of xanthine were presented. The amperometric responses of the enzyme electrodes were measured at the constant potential, which was due to the electrooxidation of enzymatically produced H2O2. Compared with XO/PVF/Pt electrode, XO/Au/PVF/Pt and XO/Pt/PVF/Pt exhibited excellent electrocatalytic activity towards the oxidation of the analyte. Effect of Au and Pt nanoparticles was investigated by monitoring the response currents at the different deposition times and the different concentrations of KAuCl4 and PtBr2. Under the optimal conditions, the calibration curves of XO/Au/PVF/Pt and XO/Pt/PVF/Pt were obtained over the range of 2.5 x 10(-3) to 0.56 mM and 2.0 x 10(-3) to 0.66 mM, respectively. The detection limits were 7.5 x 10(-4) mM for XO/Au/PVF/Pt and 6.0 x 10(-4) mM for XO/Pt/PVF/Pt. The effects of interferents, the operational and the storage stabilities of the biosensors and the applicabilities of the proposed biosensors to the drug samples analysis were also evaluated. (C) 2011 Elsevier B.V. All rights reserved.
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    EFFECT OF HEAVY METALS IMPURITIES UPON NUCLEATION KINETICS OF NaCl
    (GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2014) Ceyhan, Ayhan Abdullah; Baytar, Orhan; Gulce, Ahmet
    In this study, effects of heavy metal's impurities (Pb2+, Fe3+) on nucleation kinetics of NaCl in crystallization medium were investigated. The tests were conducted by taking into account industrial production conditions of the salt (NaCl) and taking measurements of the setting period of the solution. In the study, where the tests were carried out in both pure medium and in the presence of impurities, it was observed that the stirring process increases the nucleation rate of NaCl. It was found that heavy metal impurities significantly reduce the nucleation rate and that this effect becomes more vivid with lead ions impurities (Pb2+). The study also found that the presence of seed crystal increases the nucleation rate. However; it was also clear that the negative effects imposed by the heavy metal impurities on nucleation still kept persisting.
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    Efficient photocatalytic decolorization of some textile dyes using Fe ions doped polyaniline film on ITO coated glass substrate
    (ELSEVIER, 2013) Haspulat, Bircan; Gulce, Ahmet; Gulce, Handan
    In this study, the photocatalytic decolorization of four commercial textile dyes with different structures has been investigated using electrochemically synthesized polyaniline and Fe ions doped polyaniline on ITO coated glass substrate as photocatalyst in aqueous solution under UV irradiation for the first time. Scanning electron microscopy, atomic force microscopy, FT-IR spectra, UV-vis spectroscopy measurements were used to characterize the electrochemically synthesized polymer film photocatalyst. Film hydrophilicity was assessed from contact angle measurements. The results show that both of the polymer films exhibit good photocatalytic performance. Surprisingly, it was determined that by using Fe(II) ions during polymerization, it is possible to modify the surface roughness and wettability of the produced polyaniline films which favors their photocatalytic activity in water-based solutions. All four of the used dyes (methylene blue, malachite green, methyl orange and methyl red) were completely decolorizated in 90 min of irradiation under UV light by using Fe ions doped polyaniline at the dye concentration of 1.5 x 10(-5) M, while the decolorization of those dyes were between 43% and 83% by using polyaniline as photocatalyst. Hence, it may be a viable technique for the safe disposal of textile wastewater into waste streams. (C) 2013 Elsevier B.V. All rights reserved.
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    The Mode I interlaminar fracture toughness of chemically carbon nanotube grafted glass fabric/epoxy multi-scale composite structures
    (ELSEVIER SCI LTD, 2014) Eskizeybek, Volkan; Avci, Ahmet; Gulce, Ahmet
    A novel and simple chemical route was successfully applied to graft carbon nanotubes (CNTs) onto silanized plain weave glass fabric (PWGF) mats, as confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. The CNTs grafted PWGF mats were used to reinforce epoxy matrix for multi-scale composite production due to their potential for increasing interlaminar fracture toughness by bridging the ply interfaces. Grafting CNTs onto PWGFs improved both initial and steady-state toughness more than double as measured by Mode I interlaminar fracture testing. Failed specimens were visualized to determine the failure modes using fractography. The key findings indicated that the covalent interactions created between CNTs and fibers lead fibers bridging the interface region like "barbed wires", which are mainly responsible for increased fracture toughness as a result of improved interfacial adhesion. (C) 2014 Elsevier Ltd. All rights reserved.
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    Polyvinylferrocenium based platinum electrodeposited amperometric biosensors for lysine detection
    (ELSEVIER SCIENCE SA, 2013) Sahin, Ozlem Gokdogan; Gulce, Handan; Gulce, Ahmet
    Two amperometric biosensors based on polyvinylferrocenium (PVF+) and platinum deposited PVF+ were constructed for lysine detection. The method for modification of electrodes relied on the electrooxidation of polyvinylferrocene in methylene chloride containing tetrabutylammonium perchlorate (TBAP) at +0.70 V and electrodeposition of platinum particles on the surface of PVF+ClO4- at -0.15 V vs. Ag/AgCl. Lysine oxidase (LyOx) enzyme was immobilized by ion exchange process into modified electrodes. The response of the resulted PVF(+)LyOx(-) and PVF(+)LyOx(-)/Pt biosensors determined by oxidation of enzymatically produced H2O2 at 0.60 V vs. Ag/AgCl. The influence of experimental conditions such as applied potential, pH, temperature on the biosensor responses were examined and analytical performance characteristics of the biosensors were determined. The experimental results of two biosensors compared with each other. The results showed that PVF(+)LyOx(-)/Pt biosensor had a linear range up to 3.0 mM whereas for PVF(+)LyOx(-) biosensor that range was linear up to 1.3 mM. The detection limits of PVF(+)LyOx(-)/Pt and PVF(+)LyOx(-) biosensors were determined to be about 6.5 x 10(-4) and 5.0 x 10(-4) mM, respectively. The response time of sensors was less than 30 s. The anti-interference ability and long-term stability of the biosensors were studied. The proposed biosensors were also used to determine lysine in pharmaceutical samples. (C) 2012 Elsevier B.V. All rights reserved.
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    Preparation and mechanical properties of carbon nanotube grafted glass fabric/epoxy multi-scale composites
    (TAYLOR & FRANCIS LTD, 2017) Eskizeybek, Volkan; Avci, Ahmet; Gulce, Ahmet
    In the present paper, carbon nanotubes (CNTs) were chemically grafted onto surfaces of the amino silane-treated glass fabric by a novel chemical route for the first time to create 3D network on the glass fibers. The chemical bonding process was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. The glass fabric/CNT/epoxy multi-scale composite laminates were fabricated with the CNT grafted fabrics using vacuum assisted resin infusion molding. Tensile tests were conducted on fabricated multi-scale composites, indicating the grafting CNTs on glass fabric resulted a decrease (11%) in ultimate tensile strength while toughness of the multi-scale composite laminates were increased up to 57%. Flexural tests revealed that the multi-scale composite laminates prepared with CNT grafted glass fabric represent recovering after first load fall. The interfacial reinforcing mechanisms were discussed based on fracture morphologies of the multi-scale composites.
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    Preparation of a New Polyaniline/CdO Nanocomposite and Investigation of Its Photocatalytic Activity: Comparative Study under UV Light and Natural Sunlight Irradiation
    (AMER CHEMICAL SOC, 2013) Gulce, Handan; Eskizeybek, Volkan; Haspulat, Bircan; Sari, Fahriye; Gulce, Ahmet; Avci, Ahmet
    Polyaniline (PANI)/CdO nanocomposite was prepared for the first time in aqueous diethylene glycol solution medium, by chemical oxidative polymerization, and its photocatalytical activity was studied. Optical analysis of the new PANI/CdO nanocomposite revealed that electron densities and bond energies of the PANI homopolymer decreased after modifying with CdO nanoparticles, due to interactions between PANI chains and CdO nanoparticles. The prepared PANI/CdO nanocomposite exhibits excellent photocatalytic activity under both UV light and natural sunlight irradiation. The photocatalytic decolorization rate was increased up to 7 times after CdO addition, compared to the decolorization rate of PANI homopolymer under UV light irradiation. During the photocatalytic activity investigations, methylene blue and malachite green dyes were photocatalytically decolorized under natural sunlight irradiation with 99% efficiency by the use of 0.4 mg/mL PANI/CdO nanocomposite as photocatalyst. Furthermore, the PANI/CdO photocatalyst retains its efficiency with slight decreases upon being reused up to five times.
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    Synthesis of 3-Ethyl Indole
    (ASIAN JOURNAL OF CHEMISTRY, 2011) Karaboyaci, Mustafa; Gulce, Ahmet
    In this study, it is planned to synthesize intermediates to get beta-carboline alkaloids having effective bioligical activities. In this way, we tried to synthesize 3-ethyl indole as an intermediate from simple and cheap compounds to obtain the beta-carboline structure. This synthesis was carried out with a suitable method called the Fisher indole synthesis to synthese substitued indoles. That synthesis was tried for different acids and methods for acid catalyzed cyclization of buthenal phenylhydrazone to give 3-ethyl indole. FTIR, GSMS and NMR spectra were taken to determine the structural anaylsis of synthesized compounds.