Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Electrochemical and Oxygen/Water Permeation Behavior of Fluorinated Siloxane Copolymers Synthesized Via Initiated Chemical Vapor Deposition(Izmir Institute of Technology, 2021) Cihanoğlu, Gizem; Ebil, Özgenç; Ebil, Özgenç; 03.02. Department of Chemical Engineering; 01. Izmir Institute of Technology; 03. Faculty of EngineeringMetal-air batteries are considered as one of the best alternatives to current Li-ion batteries with their high energy densities (1000-13000 Wh/kg) also, they are lightweight, cheap, and safe. However, secondary alkaline metal-air batteries suffer from catalyst corrosion, anode passivation and corrosion, electrolyte loss, and pore-clogging leading to performance loss and reduced cycle life. This thesis aims to evaluate the feasibility of highly cross-linked, hydrophobic, and oxygen selective thin homopolymers and copolymers films as potential candidates for Gas Diffusion Layer (GDL) materials in Gas Diffusion Electrodes (GDEs) for alkaline metal-air batteries. Homopolymers of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2-(perfluorohexyl)ethyl acrylate (PFHEA) and 2-(perfluoroalkyl)ethylmethacrylate (PFEMA) and their copolymers were synthesized via initiated chemical vapor deposition (iCVD). iCVD deposited fluoropolymer thin films exhibited low water transmission rates and excellent oxygen diffusion with a high oxygen/water selectivity up to 13.6. GDEs with iCVD GDLs exhibited higher oxygen reduction current density (228.2 mA cm-2) when compared to commercial counterparts (132.7 mA cm-2). In addition, the chemical stability, durability and corrosion protection aspects of these films were investigated by substrate adhesion and immersion tests in organic solvents and NaCl solution. The results of the corrosion test together with chemical stability and durability evaluation indicate that iCVD deposited copolymers exhibit excellent adhesion, good solvent resistance and offer effective physical and chemical protection without the need for surface pretreatment. iCVD copolymer films provide better anti-corrosion barriers with lower corrosion efficiency (85-99 %) for metal surfaces compared to homopolymer counterparts. By combining siloxane and fluorinated matrix, the copolymer films provide enhanced oxygen transport and reduce moisture entrance significantly as a GDLs and also improve physical, chemical, corrosion protection.Doctoral Thesis Development of Antifouling Nanofiltration and Antibiofouling Ultrafiltration Polymeric Membranes Using Facile Protocols(Izmir Institute of Technology, 2021) Şeker, Erol; Alsoy Altınkaya, Sacide; Altınkaya, Sacide; Şeker, Erol; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyOne of the major goals in membrane separation technology is to develop fouling-resistant membranes that can provide a long operating time and low operation costs. This thesis aims to manufacture fouling and biofouling-resistant polymeric nanofiltration (NF) and ultrafiltration (UF) membranes using unique approaches. The first approach was to change coagulation bath composition in the phase inversion technique for manufacturing fouling-resistant polyamide-imide (PAI) based NF and biofouling-resistant polysulfone (PSF)/sulfonated polyethersulfone (PSF-SPES) based UF membranes. To this end, hydrophilic branched polyethyleneimine (PEI) dissolved in the coagulation bath allowed the preparation of a positively charged PAI based NF membrane by forming a covalent bond with the imide group in the PAI. To manufacture antibacterial UF membranes, a strong antibacterial surfactant, cetyltrimethylammonium bromide (CTAB), was dissolved in the coagulation bath and made an electrostatic interaction with SPES at the polymer/bath interface during phase inversion. Both membranes were prepared in a one-step process without using any pore formers in the casting solution. The second approach used in the thesis focused on modification of commercial polyethersulfone (PES) UF membranes with co-deposition of dopamine and CTAB molecules to impart antibiofouling behavior without compromising the pore size and pure water flux of the support. To achieve this task, during modification, an inert physical barrier was created inside the membrane pores by continuously feeding nitrogen gas (N2) from the backside of the support to prevent pore penetration. In the last approach, ultrasound as a green, controllable trigger was used for modifying PSF and PSF-SPES UF membranes with dopamine. The main purpose of using ultrasound was to accelerate the polymerization kinetics of dopamine, hence shortening the modification time.Doctoral Thesis Development of a Plasmonic Biosensor for Detection of Exosomes(Izmir Institute of Technology, 2020) Tekin, Hüseyin Cumhur; Bulmuş Zareie, Volga; Bulmuş Zareie, Esma Volga; Tekin, Hüseyin Cumhur; 03.01. Department of Bioengineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThe aim of this work was to develop Localized Surface Plasmon Resonance (LSPR) surfaces for quantitative detection of exosomes from different sources. For this aim, gold nanorods (AuNRs) with a mean diameter of 40 nm with an aspect ratio of 2.9 were first synthesized and characterized. The self-assembly of AuNRs on glass wafers were optimized through several experiments. In parallel, PEGylation of cetrimonium bromide (CTAB) stabilized AuNRs was investigated using PEGs with three different molecular weights via LSPR, zeta potential and XPS techniques. PEGylated AuNRs were further self-assembled on silanized microscope slides as confirmed. Surface functionalization of AuNR patterned slides was performed using alkane thiol molecules having carboxylic acid and hydroxyl functional groups and confirmed via XPS, FTIR and zeta potential. Specific antibodies (Ab) were conjugated to the surface following two different methods, i.e. click and NHS/EDC chemistry. To perform click chemistry strategy, ImmuneLink® molecules were conjugated with Abs and the final conjugate was used to functionalize surfaces prepared beforehand using azide bearing molecules. The functionalization procedure was confirmed via XPS FTIR and LSPR spectroscopy. The orientation of the antibodies on the AuNRs patterned surfaces was investigated with LSPR in comparison with conventional EDC/NHS chemistry. The click-chemistry strategy proved to provide conjugation of antibodies through their Fc regions exposing Fab regions better for antigen recognition. Finally, surfaces functionalized with a variety of antibodies were used to detect first a pregnancy-associated protein, PLAP, and then exosomes obtained from human semen samples with pre-determined exosome concentrations. The LoD of the biosensor surfaces was found to be between 103-104 exosomes/mL and 5 ng/mL (0.3 pM) PLAP. Human breast cancer cell culture samples having an unknown concentration of exosomes were further analyzed using the newly developed LSPR biochips and the exosome concentration was determined as 108 exosomes/mL for MCF-7 cell line and 107 exosomes/mL for MDA-MB-231 cell line.Doctoral Thesis Biofuels and Biochemicals Production From Microalgae Over Solid Catalysts(Izmir Institute of Technology, 2020) Şeker, Erol; Deliismail, Özgün; Şeker, Erol; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThe target of this study was the investigation of biofuel and/or biochemical production from microalgae in growth medium or its lipids over heterogenous catalyst. The primary aim was to study the conversion of 6 wt. % N. Oculata into biofuels without harvesting and dewatering over Ni-Al2O3-SiO2 catalyst at 80oC and 1 atm for 24 h. Solgel method was used to synthesize the catalyst by using the acids of H2SO4, HCl, and HNO3 to investigate the effect of acid type on catalytic activity. The catalyst prepared with H2SO4 yielded the highest conversion. The treatment of the catalyst prepared by H2SO4, with NaCl increased the conversion from 74 % to 91.5 % under same reaction conditions. The products included poly- or monosaccharides, esters and fatty acids. To achieve this conversion, Ni presence was significant beside total acidity of 25 µmol per gram of catalyst, and acidic strength ranging between 130-380oC. A new industrial application was proposed for direct conversion of 6 wt. % N. Oculata into biofuels at 80oC and 1 atm. The capacity of the plant was 1669 liters biofuel per year from 1064 liters microalgae solution per hour. The catalyst prepared with H2SO4 was used to coat either inner surface of tubes or 1-meter pluggable monoliths in tubular reactor having 20 m length and 1000 tubes each of which had 4 cm diameter. The microalgae solution was heated with Therminol®66 heated via parabolic troughs. For operation continuity, ~46000 kg of oil was stored in the tank at 120 o C for 12 h. The production of ethyl ester biodiesel from Spirulina sp. and N. Oculata lipids over 60 % CaO/Al2O3 was studied at 50oC and 1 atm. Ethanol: lipid molar ratio, catalyst amount and reaction time were investigated parameters to identify their effects on catalytic activity. The study showed that ~59 % biodiesel yield was obtained in the presence of the catalyst which was 6 wt. % of lipids, in 30 min. at ethanol: lipid molar ratio of 12 while 90 %-99 % yield was acquired at ethanol: lipid molar ratios of 24 and 48. To achieve these yields, weak basic strength in the form of bicarbonate was necessary while high basicity was not essential. Pure alumina and CaO did not yield any lipid conversion. Glycerolysis of triacylglycerol took place in series with reverse transesterification of triacylglycerol at catalyst amount which was 6 wt. % of lipids, ethanol: lipid molar ratio of 24 and 48, and 60 min. reaction time.Doctoral Thesis Development of Chitosan Based Biofoams(Izmir Institute of Technology, 2020) Polat, Mehmet; Polat, Hürriyet; Polat, Hürriyet; Polat, Mehmet; Polat, Hürriyet; 04.01. Department of Chemistry; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyChitosan is a preferred bio-foam material used in many research fields such as tissue engineering and drug delivery due to its unique structural features (wide pH stability, nontoxic-biocompatible-biodegradable, anti-inflammatory, antimicrobial). However, chitosan foams are mechanically too weak to maintain the desired shape until newly formed tissue natures. A wound infection and serious tissue necrosis, endanger human's lives. So, a dressing is required to protect loss of fluids and proteins from the wound area and prevents any bacterial invasion replacing the function of skin temporarily. Therefore controlled drug release from a wound dressing is necessary with a biocompatibility and enough mechanical strength. The aim of this study was the synthesis of mechanically durable - dual porosity chitosan bio-foams to provide a controlled drug release. For this purpose, oil droplets formed in a chitosan solution were used as templates to produce micropores that also contain vancomycin (a model antibiotic-hydrophylic) and curcumin (a model anti-inflammatory-hydrophobic) in the walls of the chitosan matrix with large structural voids. An anionic surfactant, sodium dodecyl sulfate (SDS) alone, was used as a crosslinking agent which was a new approach. Then the structures were characterized by SEM, FTIR, mechanical tests and BET analysis. The chitosan foams have dual pore structures. 1) The intrinsic micro pores that the walls of chitosan matrix have with different morphology that depends on the oil phase. 2) The structural voids that the chitosan matrix have, present even in the absence of an oil phase that depends on the experimental conditions. The mechanical strength of the foams were found to be much higher (up to 250 kPa) compare to the foams produced in literature and suggested to be suitable to use for wound dressing applications. The drug release mechanism of foams were found to depend on the conditions used for foam development and the released kinetics were presented with a mathematical model.Doctoral Thesis Catalytic Conversion of Glucose To Alkyl Glucosides(Izmir Institute of Technology, 2020) Yılmaz, Selahattin; Yılmaz, Selahattin; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyIn this study, it was pursued to develop acidic mesoporous catalysts for the synthesis of octyl glucosides. Butyl glucoside synthesis was used for catalyst screening. Tungstophosphoric acid (TPA) incorporated mesoporous silica (TPA-SBA-15), sulfated La incorporated titania-silica (SO4/La-TiO2-SiO2), organosulfonic acid functionalized mesoporous silica (Propyl-SO3-SBA-15), and sulfated mesoporous carbon (SO4/CMK-3) catalysts were prepared for this purpose. The effects of the active species (sulfates, tungstophosphoric acid and organosulfonic acid) and promoter (La) on the catalyst properties and activity were investigated. All the catalysts had mesoporous structure and high surface area. The acidity and acid site character varied depending on the catalyst type and amount of the active sites. La promoter was found effective to enhance the sulfation performance and to improve the stability of sulfates. The TPA-SBA-15 catalysts provided high glucose conversions (over 99%) and butyl glucoside yields (over 95%) due to their acidity, Keggin ion structure and pore size. The SO4/La-TiO2-SiO2 catalysts and SO4/CMK-3 catalysts were also active with glucose conversions of 74.4 % and 70 % respectively. The reaction parameters such as the reaction temperature (117 and 100 oC) and catalyst amount (20 and 30 wt% wrt. glucose) were studied in butyl glucoside synthesis over TPA-SBA-15 and SO4/La-TiO2-SiO2 which were the most active catalysts. These catalysts were found to be reusable in glycosidation with 1-butanol. Octyl glucoside synthesis was carried out via direct glycosidation. The octyl glucoside yields obtained over TPA-SBA-15 and SO4/La-TiO2-SiO2 catalysts were above 55 % and 43 % respectively. The catalysts were found promising for further investigations.Doctoral Thesis An In-Depth Study of Nucleation and Growth Processes During Stöber Silica Synthesis(Izmir Institute of Technology, 2019) Sop, Elif Suna; Polat, Mehmet; Polat, Mehmet; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologySilica nanoparticles (SNPs) which can be synthesized with high surface area, controllable morphology and desired particle size have gained significant interests in high-end applications such as catalysis, chemical sensors, cosmetics and drug delivery applications. The sol-gel technique is the most commonly applied method for manufacturing these particles owing to its simplicity and suitability for allowing surface modifications to the final product. Though monodisperse amorphous SNPs have been studied extensively, how their formation proceeds through nucleation and growth is still a topic of debate. Over the years, a number of mathematical models have been suggested for the nucleation and growth of SNPs; some suggesting that silica growth occurred through monomer addition while some arguing that aggregation of nuclei/subparticles were the dominant mechanism. Nevertheless, a clear understanding of the nucleation and growth sub-processes is extremely important in control on the size and shape of SNPs for those industrial applications which demand specific morphology and surface properties. The need for a simple, robust and generalized model, both conceptually and mathematically, to understand formation and growth of Stöber silica particles has been the main driving force for this thesis. In this study, silica synthesis was carried out under a wide variety of experimental conditions while determining the size distributions of the formed particles kinetically during different stages of the synthesis in-situ through SEM analysis using an image analysis software. The outcome of the extensive synthesis work was to obtain a clear understanding of how the formation and growth of the silica particles proceed during synthesis. This conceptual understanding of the nucleation and growth processes was then translated into a mathematical model to predict the size of the particles as a function of synthesis time.Doctoral Thesis Experimental and Computational Investigation of Transport Phenomena in Initiated Chemical Vapor Deposition (icvd) Process(Izmir Institute of Technology, 2017) Ateş, Selcan; Ebil, Özgenç; Ebil, Özgenç; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyAs a polymer thin-film deposition technique, initiated CVD (iCVD) is a heterogeneous process involving gas phase precursors and solid film formation on a solid/liquid substrates at different temperature regions. Obtaining fine-tuned film properties over different substrate geometries at different process conditions is a challenging tasks and requires experimental trials. The major goal of this study is to develop a computational model which describes all relevant transport phenomena occurring in iCVD process, and which is capable to predict the polymer film thickness at different deposition conditions for flat and/or non-flat substrates in a 3D reactor geometry. A Finite Element Analysis (FEA)-based 3D computational model, which can be applied to a variety number of iCVD reactor and substrate geometries, has been developed in the study. To validate the model, reported experimental conditions of 1H,1H,2H,2Hperfluorodecyl acrylate (PFDA) deposition with t-butyl peroxide (TBPO) initiator, and butyl acrylate (BA) deposition with t-amyl peroxide (TAPO) initiator, are applied to the model, respectively. The simulation results of both deposition processes show good agreement with experimental results reported in literature. Presented model successfully describes the relevant transport phenomena, and provides a priori predictions on polymerization rate, and film thickness on complex substrate geometries for a polymerization reaction with known kinetic data. For further studies, presented model can be modified or used as an approach for modeling of other types of CVD systems as well as facilitating process scale-up. The model can also extract valuable polymerization kinetics data provided that a sufficient number of experiments are performed at a specified substrate temperature, and process parameters and measured final film thicknesses are entered to the model.Doctoral Thesis Macromolecular Design of Hydroxyl Functional Linear and Star-Shaped L-Lactide and ?-Caprolactone Biodegradable Polyesters Utilizing Biosafe Catalysts for Biomedical Applications(Izmir Institute of Technology, 2017) Başalp, Dildare; Tıhmınlıoğlu, Funda; Tıhmınlıoğlu, Funda; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyIn the present study, macromolecular design of homo and copolymers of lactide (LA) and ε-caprolactone (CL) in different structures by the use of biocompatible catalysts and co-initiators were performed to satisfy a need of tailor-made bioassimilable polymeric structures without any hazardous metal contaminants for various medical applications. Linear and star shaped (di, tetra and hexa functional) poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) homo/copolymers were synthesized by using bismuth(III)acetate (Bi(III)Ac) and creatinine as biosafe catalysts and ethylene glycol, pentaerythritol and myo-inositol as co-initiators. The effect of catalyst type on polymer properties was observed by differences in crystalline structure. Crystalline and amorphous linear and star shaped PLLAs were obtained by using Bi(III)Ac and creatinine as catalysts, respectively. The activity of creatinine was very low comparing to Bi(III)Ac and SnOct2 catalysts. The reactivity of LA monomer was found to be higher than that of CL monomer. The high molecular weight polymers having low PDI values were obtained by using Bi(III)Ac catalyst contary to creatinine catalyst. The decrease in glass transition temperatures and molecular weights of synthesized PLLA and PCL homo/copolymers were observed with the increase in amount of co-initiators due to the decrease in chain length and disruption of crystal formation. The cytotoxicity properties of the catalysts and synthesized linear and functional homo/co PLLAs and PCLs were carried out according to MTT assay. Cytotoxicity of Bi(III)Ac was found as lower than that of SnOct2. Creatinine and the synthesized polymers did not show any cytotoxic properties. The observation of no cytotoxic effect of creatinine catalyst results in the biosafe usage of creatinine catalyst instead of toxic SnOct2 for the synthesis of moderate or low molecular weight homo/co PLLAs and PCLs in bioapplications.Doctoral Thesis Development of a Novel Hybrid Process for the Conversion of Cellulose Into High-Value Chemicals by Applying Voltage in Hot Compressed Water(Izmir Institute of Technology, 2017) Akın, Okan; Yüksel Özşen, Aslı; Yüksel Özşen, Aslı; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyIn this study, a novel hybrid method of hydrothermal electrolysis implemented for the decomposition of microcrystalline cellulose (MCC) into high value added chemicals such as levulinic acid, 5-hydroxymethylfurfural (5-HMF), and furfural. The hypothesis of the study was that, when direct current (DC) is applied the formation of ionic and radical species can alter the hydrolysis of cellulose. Based on this hypothesis, the purpose of the study was to build an integrated method of hydrothermal electrolysis that can lower energy requirement of cellulose hydrolysis by altering the selectivity. In order to investigate the individual and coupled effect of operating parameters such as reaction temperature (170-200 ℃), time (30-120 min.), electrolyte concentration (1-50 mM H2SO4), constant current (0-2 A), statistical analysis was conducted by a fractional factorial design. Analysis of variance (ANOVA) test was applied to the main hydrolysis products yields of MCC, total organic carbon (TOC) and cellulose conversion. Based on the response surface plots, 1A of current at 200 ºC maximized TOC yield and cellulose conversions to 62% and 81%, respectively. In order to enhance the selectivity, constant voltage (2.5, 4.0 and 8.0 V) was applied at 200℃. Application of 2.5 V increased TOC (54%) and alter the selectivity of 5-HMF (30%) and levulinic acid (21%). The structural changes in solid residues were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and found that MCC particles functionalized by carboxylic acid and sulfonated groups by application of 2.5 V. Therefore, change in the selectivity values were conducted with the functionalization of MCC particles due to applied voltage under sub-critical conditions.