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    Effect of Au and Au@ag Core-Shell Nanoparticles on the SERS of Bridging Organic Molecules
    (ACADEMIC PRESS INC ELSEVIER SCIENCE, 2010) Güzel, Remziye; Üstündağ, Zafer; Ekşi, Haslet; Keskin, Selda; Taner, Bilge; Durgun, Zeynep Gülşah; Turan, Aybüke A. İşbir; Solak, Ali Osman
    Gold nanoparticles (AuNPs) with about 6 nm size were produced and stabilized with mercaptopropionic acid (MPA) film to produce a monolayer protected cluster (MPC) of AuS(CH2)(2)COOH. 4-Aminothiophenol (ATP) molecules were introduced to the activated carboxylic acid ends of the film surrounding the AuNPs to produce AuS(CH2)(2)CONHPhSH MPC. These modified AuNPs were again self-assembled with Au@Ag core-shell bimetallic nanoparticles via the -SH groups to produce an organic bridge between Au and Au@Ag metallic nanoparticles. An unusually strong enhancement of the Raman signals was observed and assigned to the plasmon coupling between the AuNPs and Au@Ag NPs bridged assembly. Formation of AuS(CH2)(2)COOH and AuS(CH2)(2)CONHPhSH clusters and AuS(CH2)(2)CONHPhS(Au@Ag) assembly is confirmed by UV-Vis, reflection-absorption IR spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS), as well as by TEM analysis. The SERS activity of the AuNPs and Au@Ag NPs was tested using the HS(CH2)(2)CONHPhSH molecule as a probe to compare the effectiveness of monometallic and bimetallic systems. SERS spectra show that Au@Ag bimetallic nanoparticles are very effective SERS-active substrates.
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    Fabrication of Calix[4]pyrrole Nanofilms at the Glassy Carbon Surface and Their Characterization by Spectroscopic, Optic and Electrochemical Methods
    (Elsevier Science Sa, 2010) Taner, Bilge; Özcan, Emine; Üstündağ, Zafer; Keskin, Selda; Solak, Ali Osman; Ekşi, Haslet
    meso-Octamethylcalix[4]pyrrole (CP) and meso-heptaethylcalix[4]pyrrole-meso-4-aminophenyl (4APCP) modified glassy carbon (GC) electrodes were prepared by the electrochemical oxidation in acetonitrile solution. Binding of the calix[4]pyrroles with the glassy carbon surface was investigated that it is through the etheric linkage revealed from the reflection absorption infrared spectroscopy (RAIRS). Surface films of CP and 4APCP were investigated by cyclic voltammetry (CV), ellipsometry, X-ray photoelectron spectroscopy. RAIRS and the contact angle measurements. The thicknesses of the films were determined by ellipsometry which confirmed that the film was multilayer and homogeneous over the surface. Ellipsometric measurements also provided that the CP and 4APCP film thicknesses were 2.49 nm and 4.58 nm for 6 CV cycle modification, corresponding to 66 mu F/cm(2) and 106 mu F/cm(2) capacitances obtained by CV. The wetting behavior was examined by contact angle measurements and found that the hydrophobicity of the GC-4APCP surface was higher than that of GC-CP, probably due to the aromatic meso substituent present in the former.
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    Modification of glassy carbon electrode by the electrochemical oxidation of 3-aminophenylcalix[4]pyrrole in nonaqueous media
    (Wiley, 2012) Taner, Bilge; Deveci, Pervin; Üstündağ, Zafer; Keskin, Selda; Özcan, Emine; Solak, Ali Osman
    3-Aminophenylcalix[4]pyrrole (3APCP) was grafted to a glassy carbon (GC) surface during the electrochemical oxidation process in 0.1 M tetrabutylammoniumtetra-fluoroborate (TBATFB) containing acetonitrile solution. The presence of a surface film was confirmed electrochemically by comparing voltammograms of dopamine and ferricyanide redox probes at the bare and modified electrodes. Reflection-absorption infrared spectroscopy (RAIRS), XPS, atomic force microscopy (AFM), ellipsometry and the contact angle measurements were also employed to characterize 3APCP film on GC electrode. RAIRS analysis revealed that calix[4]pyrrole was bonded to the glassy carbon surface via the etheric linkage. The stability of the modified GC electrode was also studied. Copyright (C) 2011 John Wiley & Sons, Ltd.
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    Preparation and Properties of Electrospun Poly(vinyl alcohol) Blended Hybrid Polymer with Aloe vera and HPMC as Wound Dressing
    (2010) Uslu, İbrahim; Keskin, Selda; Gül, Ali; Karabulut, Tutku Ceren; Aksu, Mehmet Levent
    A series of poly(vinyl alcohol) (PVA)/poly(vinyl pyrrolidone) (PVP)/poly(ethylene glycol) (PEG) hybrid nanofibers were fabricated by an electrospinning method, in order to be used as a potential wound dressing material. The effect of Aloe vera was investigated in terms of solution properties such as viscosity, conductivity, pH and surface tension. The nanofibrous wound dressing materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC). SEM results revealed that the fiber diameters ranged between 200-500 nm and they were linear, homogenous and free of beads. DSC thermograms indicated that the addition of Aloe vera affects the crystal structure and efficiently cross-links the hybrid polymer, forming an amorphous structure with a melting temperature (Tm) of 219°C at an Aloe vera concentration of 3%. FTIR results clearly resolved the hybrid polymer structure of nanofibers obtained.
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    Preparation of Gadolina Stabilized Bismuth Oxide Doped with Boron via Electrospinning Technique
    (SPRINGER, 2012) Tunç, Tuncay; Uslu, İbrahim; Durmuşoğlu, Şenol; Keskin, Selda; Aytimur, Arda; Akdemir, Ahmet
    In this study, boron doped and undoped poly (vinyl) alcohol/bismuth-gadolina acetate (PVA/Bi-Gd) nanofibers were prepared using electrospinning technique then calcinated at 800 degrees C for 2 h. The originality of this study is the addition of boron to metal acetates. The effects of boron doping were investigated in terms of solution properties, morphological changes and thermal characteristics. The characteristics of the fibers were investigated with FT-IR, XRD, SEM and BET. The addition of boron did not only increase the thermal stability of the fibers, but also their diameters, which yielded stronger fibers. XRD analyses showed that boron doping increased the peak intensities and indicated that the boron doping enhanced the crystallite size. Moreover, no shifts were noticed in diffraction angles for boron doped and undoped samples. Therefore, boron doping did not significantly alter the lattice spacing. The SEM micrograph of the fibers showed that the addition of boron resulted in the formation of cross-linked bright-surfaced fibers. The average fiber diameter for boron doped and undoped fiber mats were 204 and 123 nm, respectively. Also, grain diameters of boron doped and undoped nanocrystalline sintered powders were measured as 140 and 118 nm, respectively. The BET results showed that boron undoped and doped Bi2O3-La2O3 nanocrystalline powder ceramic structures sintered at 800 degrees C have surface areas of 59.72 and 39.80 m(2)/g, respectively.
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    Synthesis and characterization of boron-doped Bi2O3-La2O3 fiber derived nanocomposite precursor
    (SPRINGER, 2011) Durmusoglu, Senol; Uslu, Ibrahim; Tunc, Tuncay; Keskin, Selda; Aytimur, Arda; Akdemir, Ahmet
    Boron doped poly(vinyl) alcohol/ bismuth - lanthanum acetate (PVA/Bi-La) nanofibers were prepared by electrospinning using PVA as a precursor. The effect of boron doping was investigated in terms of solution properties, morphological changes and thermal characteristics. The fibers were characterized by FT-IR, XRD, SEM and BET. The addition of boron did not only increase the thermal stability of the fibers, but also their diameters, which yielded stronger fibers. XRD analyses showed that boron doping increased the peak intensities and indicated that the boron doping enhanced the crystallite size. Moreover, no shifts were noticed in diffraction angles for boron doped and undoped samples. Therefore, boron doping did not significantly alter the lattice spacing. The SEM micrograph of the fibers showed that the addition of boron resulted in the formation of cross linked bright surfaced fibers. Also, grain diameters of boron doped and undoped nanocrystalline sintered powders were measured as 170 nm and 120 nm respectively. The BET results show that boron undoped and doped Bi2O3-La2O3 nanocrystalline powder ceramic structures sintered at 800 A degrees C have surface areas of 20.44 m(2)/g and 12.93 m(2)/g, respectively.