Browsing by Author "Ertas Y."
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Item Open Access Enhanced thermal stability of eugenol by cyclodextrin inclusion complex encapsulated in electrospun polymeric nanofibers(American Chemical Society, 2013) Kayaci, F.; Ertas Y.; Uyar, TamerPolyvinyl alcohol (PVA) nanofibers encapsulating eugenol (EG)/cyclodextrin (CD) inclusion complexes (IC) (EG/CD-IC) were produced via electrospinning technique in order to achieve high thermal stability and slow release of EG. In order to find out the most favorable CD type for the stabilization of EG, three types of native cyclodextrins (α-CD, β-CD, and γ-CD) were used for the formation of EG/CD-IC. In the case of PVA/EG/α-CD nanofibers, uncomplexed EG was detected indicating that α-CD is not a proper host for EG/CD-IC formation. However, for PVA/EG/β-CD-IC and PVA/EG/γ-CD-IC nanofibers, enhanced durability and high thermal stability for EG were achieved due to the inclusion complexation. The electrospun nanofibers encapsulating CD-IC of active compounds such as eugenol may be quite useful in the food industry due to the extremely large surface area of nanofibers along with specific functionality, enhanced thermal stability, and slow release of the active compounds by CD inclusion complexation. © 2013 American Chemical Society.Item Open Access Excitation dependent recombination studies on SnO2/TiO2 electrospun nanofibers(Royal Society of Chemistry, 2015) Babu, V. J.; Vempati S.; Ertas Y.; Uyar, TamerPoly(vinyl acetate) (PVAc)/TiO2 nanofibers, PVAc/SnO2 nanoribbons and PVAc/SnO2-TiO2 nanoribbons were produced via electrospinning. TiO2 nanofibers and SnO2 nanoribbons were obtained by removal of the polymeric matrix (PVAc) after calcination at 450 °C. Interestingly, PVAc/SnO2-TiO2 nanoribbons were transformed into SnO2-TiO2 nanofibers after calcination under the similar conditions. Fiber morphology and elemental mapping confirmed through SEM and TEM microscope techniques respectively. The X-ray diffraction measurements suggested the presence of anatase TiO2 and rutile SnO2 and both were present in the SnO2-TiO2 mixed system. Systematic photoluminescence studies were performed on the electrospun nanostructures at different excitation wavelengths (λex1 = 325, λex2 = 330, λex3 = 350, λex4 = 397 and λex5 = 540 nm). We emphasize that the defects in the SnO2-TiO2 based on the defect levels present in TiO2 and SnO2 and anticipate that these defect levels may have great potential in understanding and characterizing various semiconducting nanostructures.Item Open Access Optoelectronic properties of layered titanate nanostructure and polyaniline impregnated devices(Wiley - V C H Verlag GmbH & Co. KGaA, 2016) Vempati S.; Ertas Y.; Babu, V. J.; Uyar, TamerIntegrated structure of titanate nanotubes and nanosheets is investigated for their optical, electronic and optoelectronic properties when combined with HCl doped polyaniline (PANI). HR-TEM, SEM and XRD were employed for detailed morphological and microstructural understanding of the orthorhombic titanate nanostructure. Chemisorbed oxygeneous groups are probed with Raman spectroscopy which are found to desorb under UV-Vis treatment. We note a blue shift of Ti-O-Ti Raman frequency in contrast to Na-O-Ti stretching. Valence band region of titanate is analyzed for contribution of O2p, O2s, Na2p and Ti3p. Photoluminescence with different excitation energies revealed the presence of oxygen vacancy related defects in titanate. The highly occupied electronic states of PANI were also analyzed until 40 eV below the Fermi energy. XPS core-level analyses revealed ∼25 % doping density in PANI. Edges of valence band and HOMO are determined to be at 2.45 eV and 2.54 eV below Fermi energy for titanate and PANI, respectively. ITO/PANI/ITO has depicted negative photoresponse and the magnitude of which is reduced ∼4 times after combining with titanate nanostructure. Essentially the nanoscale architecture separates the emeraldine base and salt regions of PANI. This separation channelizes the charge carriers before trapping which reduces the magnitude of the negative photoresponse.