Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/4719

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Author: search.filters.author.Kap, Özlem

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Now showing 1 - 5 of 5
  • Article
    Citation - WoS: 10
    Citation - Scopus: 12
    Li-Ion Battery Cathode Performance From the Electrospun Binary Licoo2 To Ternary Li2coti3o8
    (Springer Verlag, 2020) Kap, Özlem; İnan, Alper; Er, Mesut; Horzum, Nesrin
    Metal oxide nanofibers are prepared by electrospinning and are developed to be the electrodes for lithium-ion batteries (LIBs). The effect of calcination temperature and the Li:Co mole ratio of LiCoO2 nanofibers was investigated on the electrochemical cathode performance in a coin cell battery. The higher temperature calcination and Li:Co mole ratio have improved the electrochemical performance of the nanofibers. Lithium cobalt oxide (LiCoO2) nanofibers obtained at 400 and 700 degrees C retain 65% and 90% of the initial capacity, respectively, after the high-current test and the C-rate reverted to 0.1 C. When doubling the mole ratio of Li:Co (2:1), an increase in specific capacity values from 78 to 148 mAh g(-1) has been provided. Additionally, colloidal titania nanoparticles (TiO2 NPs)-doped LiCoO2 nanofibers were obtained and investigated as a cathode material. While the increment in calcination temperature results in higher crystallinity and stability of the LiCoO2 phase, in the presence of the TiO2 NPs causes a transformation of binary (LiCoO2/TiO2) to ternary Li-based transition metal oxide (Li2CoTi3O8/TiO2). An initial discharge capacity of 82 mAh g(-1) was found at 0.1 C for the Li2CoTi3O8/TiO2 nanoparticles and the capacity retention was 83% when returned to 0.1 C after 25 cycles.
  • Article
    Citation - WoS: 31
    Citation - Scopus: 34
    Dual Remediation of Waste Waters From Methylene Blue and Chromium (vi) Using Thermally Induced Zno Nanofibers
    (Elsevier, 2020) Elhousseini, Mohamed Hilal; Isık, Tuğba; Kap, Özlem; Verpoort, Francis; Horzum, Nesrin
    Electrospun zinc oxide (ZnO) nanofibers have been significantly improved via a simple heat treatment modification. The present work reports an intriguing cost-effective microstructure tuning, by drastically dropping the temperature of the calcined sample during the cooling period, to get highly photocatalytically active ZnO nanofibers. The calcination temperatures are deducted from thermogravimetric analysis, the phase and purity are confirmed by X-ray diffraction, while the morphology and texture have been revealed by field emission scanning electron microscopy and high-resolution transmission electron spectroscopy. X-ray photoelectron spectroscopy was conducted to get further insight on the surface composition and oxidation states, while N-2-adsorption isotherms were analyzed using the Brunauer-Emmet-Teller methodology. The crystallinity, surface area, and porosity of the ZnO nanofibers, as well as the exposure of active sites, have been enhanced by the rapid cooling method. Photodegradation activity toward methylene blue was improved from 88% to 94%, and 85% to 97%, for free cooled and rapid cooled samples calcined at 300 degrees C and 500 degrees C respectively. The adsorption of chromium (VI) was also tested and reached around 85 mg/g at 100 ppm without being saturated, thereby highlighting one of the most cost-effective performance-enhancing modifications so far that could be extended on different metal oxide nanomaterials.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 11
    Structural Stability of Physisorbed Air-Oxidized Decanethiols on Au(111)
    (American Chemical Society, 2020) Kabanoy, Nikolai; Tsvetanova, Martina; Klaysyuk, Andrey L.; Zandvliet, Harold J. W.; Sotthewes, Kai; Kap, Özlem; Varlıklı, Canan
    We have studied the dynamic behavior of decanethiol and air-oxidized decanethiol self-assembled monolayers (SAMs) on Au(111) using time-resolved scanning tunneling microscopy at room temperature. The air-oxidized decanethiols arrange in a lamellae-like structure leaving the herringbone reconstruction of the Au(111) surface intact, indicating a rather weak interaction between the molecules and the surface. Successive STM images show that the air-oxidized molecules are structurally more stable as compared to the nonoxidized decanethiol molecules. This is further confirmed by performing current-time traces with the feedback loop disabled at different locations and at different molecular phases. Density function theory calculations reveal that the diffusion barrier of the physisorbed oxidized decanethiol molecule on Au(111) is about 100 meV higher than the diffusion barrier of a chemisorbed Au-decanethiol complex on Au(111). A two-dimensional activity map of individual current-time traces performed on the air-oxidized decanethiol phase reveals that all the dynamic events take place within the vacancy lines between the air-oxidized decanethiols. These results reveal that the oxidation of thiols provides a pathway to produce more robust and stable self-assembled monolayers at ambient conditions.
  • Article
    Citation - WoS: 12
    Citation - Scopus: 12
    Ordering of Air-Oxidized Decanethiols on Au(111)
    (American Chemical Society, 2018) Sotthewes, Kai; Kap, Özlem; Wu, Hairong; Thompson, Damien; Huskens, Jurriaan; Zandvliet, Harold J. W.
    Self-assembled monolayers (SAMs) of alkanethiols on gold are a commonly used platform for nanotechnology owing to their ease of preparation and high surface coverage. Unfortunately, the gold-sulfur bond is oxidized at ambient conditions which alters the stability and structure of the monolayer. We show using scanning tunneling microscopy and X-ray photoelectron spectroscopy that decanethiolate molecules oxidize into decanesulfonates that organize into a hitherto unknown striped phase. Air-exposed SAMs oxidize, as can be determined by a shift of the S 2p peak and the appearance of O 1s photoelectrons as part of the decanethiol monolayer transforms into a lamellae-like decanesulfonate structure when exposed to air. The herringbone structure of the Au(111) surface is preserved, indicating that the interaction between the molecules and the surface is rather weak as these findings are substantiated by density functional theory calculations.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 13
    Anticorrosion Coating for Magnesium Alloys: Electrospun Superhydrophobic Polystyrene/Sio2 Composite Fibers
    (TUBITAK, 2018) Horzum Polat, Nesrin; Kap, Özlem; Farzaneh, Amir
    Superhydrophobic nanocomposite coatings for magnesium surfaces with remarkable corrosion resistance were fabricated by electrospinning in the presence of fluorosilane-functionalized silica (SiO2) nanoparticles. The effects of surface-modified silica (mod-SiO2) nanoparticles on the superhydrophobicity and corrosion resistance of polystyrene (PS)/mod-SiO2 fiber coatings were evaluated. The incorporation of the SiO2 nanoparticles endows PS fibers with rough surfaces exhibiting a water contact angle (WCA) of 165◦. The surface wettability, corrosion resistance, and their relation to the inorganic content in the PS fibers and the contact angle of the composite coatings were explored. Analysis of the corrosion results confirmed that the PS/mod-SiO2 coating protected the Mg surface from corrosion. In addition, PS fibers containing mod-SiO2 nanoparticles showed improved hydrophobicity, and excellent corrosion resistance was achieved with PS fibers containing 4 wt% SiO2 nanoparticles.