Phd Degree / Doktora

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Access Right: Embargoed AccessDepartment: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Chemistry

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Now showing 1 - 4 of 4
  • Doctoral Thesis
    Development of New Chemometrics Approaches To Determine Physical and Chemical Properties of Crude Distillation Unit Products Based on Molecular Spectroscopy
    (01. Izmir Institute of Technology, 2022) Meşe Sezen, Ayten Ekin; Özdemir, Durmuş
    Crude distillation units are the first processing units of crude oils based on fractional distillation. The properties of the petroleum products obtained from refinery units are frequently analyzed to ensure that the off-spec product cannot be obtained and that the process is working under the desired conditions. This study aims to develop a method based on multivariate data analysis to determine physical and chemical properties of petroleum samples as an alternative to time-consuming and conventional analytical methods. Four different petroleum products obtained from CDU for years were selected and used in this study, which are heavy and light diesel, heavy and light straight run naphtha. Four different spectroscopic methods which are UV-Vis, Fluorescence, FT-NIR and FTIR-ATR spectroscopy, were performed and compared. Multivariate calibration models were developed using Partial least Squares (PLS) and Genetic Inverse Least Squares (GILS) algorithms. For heavy and light diesel, predictive performance of three different spectroscopic methods were compared and for heavy diesel UV-Vis spectroscopy, for light diesel FT-NIR spectroscopy was selected for most of the parameters. Developed models by fluorescence analysis of light diesel samples conducted with two different measurement modes and synchronized fluorescence spectral data has resulted in better models compared to total fluorescence spectra. Studies with straight run naphtha samples were obtained from three different refineries and prediction performances were compared. All obtained model results indicates that developed methodology can be used in routine operations instead of conventional analytical methods.
  • Doctoral Thesis
    Preparation of Nanostructured Interface by Polymer Grafting on Various Solid Substrates for Biosensor Applications
    (Izmir Institute of Technology, 2021) Özenler, Sezer; Yıldız, Ümit Hakan
    This thesis presents the utilization, various applications, and characterization of the soft material-based coating formed on the gold surface with varying thickness and chemical properties resulting from the isocyanate-gold interaction. Theoretical calculations regarding the interaction of isocyanate with the gold surface revealed the character of the bond formed and the orientation of the functional groups on the surface. Results by X-ray photoelectron spectroscopy showed the tendency to shift to the high energy at N 1s and C 1s binding energies in the gold-interacting isocyanate group. In the next steps, the isocyanate-activated gold substrate was subjected to sequential incubation of 1,4-butanediol/hexamethylene diisocyanate, and thin-film formation was achieved by surface assisted (SurfAst) urethane polymerization. It was revealed with three different applications that a nano-porous polyurethane (PU) structure was formed on the gold substrate and could be postmodified by using SurfAst polymerization method. In the first application, modification with polyethylene glycol (PEG) was provided to obtain antifouling properties. The PEG-terminated PU structure on the gold surface was shown to reduce protein adhesion by approximately ten-fold. In the second application, SurfAst was applied on the 11-mercaptodecanoic acid incubated surface and grafting onto the poly (N-allyl-N-methyl-N-(3-((4-methylthiophen-3-yl)oxy)propyl) prop-2-en-1-aminium surface was characterized. As a result of PT grafting, PT nanowires with an average height of 100 nm, a width of 250 nm, and a length of 7 μm were obtained on the gold surface. In the last application, a soft nanogel was obtained by a reactive layer-layer (rLBL) coating method using the aza-Michael addition reaction of branched polyethyleneimine and polyester on the isocyanate functional surface. The mechanical and electrical permeability and coating properties of the nanogel layer were assessed. In conclusion, the high potential of isocyanate in surface activation has been demonstrated theoretically and experimentally. Effective modification of gold surfaces by polymer grafting with the SurfAst method and rLBL coating techniques has been achieved.
  • Doctoral Thesis
    Investigation of Carotenoid Contents of Various Microalgae by Chromatographis/Spectroscopic Methods
    (Izmir Institute of Technology, 2013) Erdoğan, Ayşegül; Eroğlu, Ahmet Emin
    Microalgae are the most important energy sources among microorganisms. Carotenoids, as important pigments and antioxidants, are produced by microalgae and are used both for health purposes and as natural colorants. There has been considerable research for the development, identification and determination of new strains of organisms to produce a variety of carotenoids. New methods for the isolation of carotenoids should be developed also for analytical purposes. This study aimed the biosynthesis of carotenoids from microalgae, (Prochlorococcus sp., Scenedesmus protuberans and Nitzschia sp.) their identification and quantification. It is known that some types of microalgae can produce high amount of carotenoids under different stress conditions while some others can produce carotenoids only under stress. For this purpose, cultivation conditions were optimized for the production of new or high value of carotenoids in the selected microalgal strains. Freeze-dried microalgae were extracted using different organic solvents and their carotenoid contents were investigated by high performance liquid chromatography (HPLC) and other chromatographic techniques such as liquid chromatography-mass spectrometry (LC-MS); in addition to (UV-VIS) spectroscopy. In green microalgae lutein (2.54 mg/g for Prochlorococcus sp. and 2.45 mg/g for Scenedesmus protuberans) is the most abundant carotenoid. On the other hand, in brown microalga fucoxanthin (6.58 mg/g for Nitzschia sp.) is the highly accumulated carotenoid. Under stress conditions, many microalgae alter their biosynthetic pathways for the formation and accumulation of carotenoids. Therefore, the effect of different nitrogen sources, oxidative stress conditions and different light sources on lutein content in green microalgae and on fucoxanthin content in brown microalga were investigated.
  • Doctoral Thesis
    Synthesis and Control of Exciton Dynamics in Cdte, Cdte/Cds and Znxcd1-Xte Colloidal Nanocrystals
    (İzmir Institute of Technology, 2012) Eral Doğan, Leyla; Özçelik, Serdar
    The aim of this study is to synthesize cadmium-based semiconductor colloidal nanocrystals and to control their exciton dynamics by tuning the size and composition of the nanocrystals (NCs). CdTe, CdTe/CdS binary, and ZnxCd1-xTe ternary semiconductor NCs are prepared by wet chemistry. The reactions are thoroughly optimized to enhance the optical properties. The optical properties of CdTe and CdTe/CdS are tuned by the size of the NCs by adjusting the reaction (the growth) time. Coating CdTe NCs with CdS layer enhances the photoluminescence quantum yields up to 45%. ZnxCd1-xTe ternary nanoalloys were synthesized by varying the initial mole ratios of metals (Zn/Zn+Cd) and the growth time. The size and the composition-tunable ZnxCd1-xTe nanoalloys exhibit highly luminescent optical properties. When the amount of initial Zn precursor is low, the nanoalloys have Cd-rich and Zn-poor internal crystal structure. However, at higher amount of Zn precursor, the nanoalloys have Zn-rich and Cd-poor core exhibiting gradient composition. The exciton interactions and dynamics are investigated as a function of the size of CdTe/CdS, and the composition and the size of ZnxCd1-xTe nanoalloys. The exciton interaction yields amplification in the output signal at the threshold of 1015 photon/cm2s per laser pulse. The exciton lifetimes are in the range of picoseconds to nanoseconds. The decay associated spectra are affected by the laser power, size and composition of the NCs. As the laser power increases new excitonic states are created especially in ZnxCd1-xTe nanoalloys. Multiexcitons were created in the NCs depending on the laser power. Small NCs exhibit stronger exciton-exciton interactions under high laser power compared to larger NCs. However larger NCs have lesser exciton density, therefore reducing the exciton-exciton interactions.