Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Synthesis and Characterization of Doped Defective Titania Based Photocatalysts for Hydrogen Generation(01. Izmir Institute of Technology, 2025) Gözel, Gözde; Top, AybenSera gazlarındaki artış, sürdürülemez fosil yakıtların yaygın kullanımıyla yoğunlaşarak sera etkisini artırmış ve bu da küresel ısınma ve iklim değişikliğine yol açmıştır. Yapay fotosentez, küresel CO2 seviyelerini azaltırken metan, metanol ve hidrojen gibi yenilenebilir, sürdürülebilir yakıtlar üretmek için umut verici bir tekniktir. Benzersiz optik ve kimyasal özellikleriyle bilinen titanyum bazlı fotokatalitik malzemeler, yapay fotosentezde yaygın olarak kullanılmakta olup, yakın zamanda sentezlenen siyah nano titanya malzemeleri de dahil olmak üzere nano tasarımlı hatalı TiO2 yapıları, UV veya güneş ışığı ile çalışan fotokatalitik hidrojen üretimi için en umut verici adaylardan bazıları olarak ortaya çıkmaktadır. Bu çalışmada, hatalı TiO2 bazlı fotokatalizörler sentezlenmiş ve geliştirilmiş fotokatalitik verimlilik potansiyellerini araştırmak için karakterize edilmiştir. Saf TiO2, hidrosol ve çöktürme yöntemleri kullanılarak sentezlenmiş, ardından kusurların oluşturulması için NaBH4 indirgeme maddesi ile indirgenmiştir. Hidrosol yöntemiyle üretilen hatalı TiO2 nanomalzemeler, indirgeme sıcaklığı ve TiO2-NaBH4 ağırlık oranı gibi indirgeme koşullarının optimize edilmesine odaklanırken, çöktürme yöntemi ön ısıtma işlemi ve indirgeme stratejileri içermektedir. Malzemelerin yapısal/optik özelliklerini analiz etmek için XRD, SEM, BET, ATR-FTIR, PL, UV-Vis spektroskopisi ve GC analizi gibi gelişmiş karakterizasyon teknikleri uygulanmıştır. Hidrosol yöntemiyle üretilen hatalı TiO2 nanomalzemeler, 325°C indirgeme sıcaklığında ve TiO2-NaBH4 (1:1) ağırlık oranıyla en yüksek hidrojen verimini elde etmiştir. Çökeltme yöntemiyle üretilen hatalı TiO2 nanomalzemeler ise 500°C'de ön ısıtma sonrasında optimum aktivite göstermiştir. Zr/Nd katkı maddesiyle yapılan katkılama çalışmaları, katkılanmamış fotokatalizörlere kıyasla hidrojen üretim verimliliğini artırmıştır.Doctoral Thesis Valorization of Lignocellulosic Waste Abundant in Türkiye for Potential Application in Sustainable Lithium Recovery(01. Izmir Institute of Technology, 2023) Recepoğlu, Yaşar Kemal; Özşen, Aslı YükselThe demand for lithium (Li) is increasing by its pivotal role in energy storage and transportation electrification nowadays. The surge in demand has prompted a global quest for sustainable and cost-effective methods to extract Li from water sources. This thesis centers on valorizing abundant lignocellulosic waste, specifically hazelnut shell waste, abundant in Türkiye starting with the phosphorylation of pristine cellulose, contributing to the development of innovative biosorbents tailored for extracting Li from aqueous solutions. Comprehensive material characterization was conducted using SEM–EDS, FTIR, XPS, BET, XRD, and TGA analyses. Various factors influencing the process, such as biosorbent dosage, initial concentration, temperature, contact time, pH, and coexisting ions were explored. The maximum sorption capacity was determined to be 9.60 mg/g for phosphorylated functional cellulose (FC) and 7.71 mg/g for phosphorylated functional hazelnut shell waste (FHS) at 25°C, by the Langmuir model. Impressively, Li sorption reached equilibrium within a 3-minute, indicating the rapid kinetic properties of biosorbents. Furthermore, FC and FHS were employed in a packed bed column, leading to a threefold increase in sorption capacity under dynamic flow, especially at lower flow rates, regardless of bed height. Remarkably, a mere 15.75 mL of 5% H2SO4 solution was adequate to desorb approximately 100% of Li from the saturated biosorbents. The column data interpreted with theoretical models, affirmed the potential for large-scale implementation of these biosorbents. Preliminary tests on Li recovery from geothermal water using FC and FHS were also conducted to assess their applicability in real brine conditions, with a comparison made to the commercial ion exchange resin, Lewatit® TP 260.Doctoral Thesis Chemical Vapor Deposited Reusable Fluorescent Thin Film Sensor Nanoprobes for the Detection of Heavy Metal Ions(01. Izmir Institute of Technology, 2023) Karabıyık, Merve; Ebil, ÖzgençHeavy metal pollution has made a serious threat to the environment and human health day by day due to developing science, technology and industrial activities, therefore, the importance of selective detection of heavy metals has increased. Heavy metals gradually accumulate in the human body, especially via water sources. Among heavy metals, cadmium is one of the most carcinogenic ones and has harmful effects even in trace amounts. Despite it, detection studies of cadmium ion are very few. This thesis study focuses on the development of Initiated Chemical Vapor Deposition (iCVD) synthesized polymer thin film based quantum dot-nitroxide radical fluorescence sensor nanoprobe, which has a multi-use property and high durability, unlike sensor probes developed for single use in liquid media, and selective detection of Cd2+ ions in real water sources. By examining the effects of pH, concentration, solvent type and reaction time, the most suitable conditions to improve the interaction between Cd2+ ion and the newly developed sensor nanoprobe were investigated. The results proved that it is possible to detect the target ion easily even in complex environments where other heavy metal ions are present. Cd2+ ion detection limit with this proposed nanoprobe was found as 0.195 μM and high recovery percentage (>90%) obtained in standard addition method. In the multi-use study, it was confirmed that nanoprobe could be used repeatedly for the selective and sensitive detection of Cd2+ ion without being influenced by the content of daily water samples. This thesis is a great guide for new fluorescent sensor applications.Doctoral Thesis Removal of Dyes and Antibiotics by Adsorption and Photocatalytic Degradation Using Zn-Based Composites(01. Izmir Institute of Technology, 2023) Saygı, Gizem; Çakıcıoğlu Özkan, Seher FehimeIn this study, the ZIF-8 was synthesized and immobilized on the clinoptilolite surface (ZIF8@CLN) and doped with Ag nanoparticles, forming the Ag-ZIF8 and Ag-ZIF8@CLN composite materials. The characterization results indicated that the ZIF-8 was well-deposited on the clinoptilolite surface and doped successfully with Ag nanoparticles. The adsorption and photocatalytic activity of these adsorbents/catalysts were evaluated by the removal of the organic pollutants such as dyes and antibiotics. The target dyes were cationic Methylene blue (MB), anionic Methyl orange (MO) and Congo red (CR), and zwitterionic Rhodamine B (RhB). The target antibiotic was tetracycline (TC). The influence of various parameters on removal was investigated using different initial pH, photocatalyst amount, pollutant concentrations and ionic strength. The results showed that ZIF-8 and ZIF-8@CLN are excellent adsorbents. However, the photocatalytic activity of Ag-ZIF8 and especially Ag-ZIF8@CLN composites were much better than ZIF-8 and ZIF-8@CLN for degradation of all dyes. The Ag-ZIF8 and Ag-ZIF8@CLN composite catalysts exhibited more than 90% removal capacity under UV irradiation for 120 min with the dye concentration of 25 mg L-1 at the optimum pHs of each dye. The enhanced adsorption and photocatalytic performance of the composite photocatalysts was attributed to the synergistic effect between the ZIF-8, CLN and Ag. The adsorption data were evaluated by considering adsorption isotherms, kinetics and thermodynamics using target dyes and antibiotics. Proposed photodegradation mechanism of the dyes over Ag-ZIF8@CLN was explained detailed. This work introduced the ZIF-8-based composite photocatalysts with high efficiency, and may provide to prefer these catalysts in photocatalytic field.Doctoral Thesis Development of Innovative Polymeric Membranes Using Green Approaches for Water and Energy Sustainability(01. Izmir Institute of Technology, 2022) Güngörmüş Deliismail, Elif; Altınkaya, SacideIn this thesis, innovative polymeric membranes with fast, simple, and easily scalable manufacturing procedures were developed to demonstrate the potential of membrane technology in making chemical processes more sustainable. In this scope, firstly, it was focused on minimizing the adverse chemical, environmental, and economic effects of conventional drying processes by integrating membrane technology into the production of nano/microparticles. Acid-resistant polyaniline based ultrafiltration (UF) membrane and solvent-resistant poly (ether imide sulfone) based UF membrane were developed to produce aluminum sulfate powder and silica powder, respectively. The developed high-performance and antifouling membranes made the production of powders more sustainable and environmentally friendly by enabling the recovery of the acid/solvent used in the synthesis and the reduction of energy consumption for drying. The third part of the thesis focused on biodiesel production with a high-performance, antifouling, alumina-calcium oxide catalyst-modified polyethersulfone UF membrane. Combining membrane technology with reaction engineering allowed for the elimination of the catalyst recovery step, shortened the reaction time to reach a desirable yield, and reduced energy consumption, resulting in more sustainable biodiesel production than existing production techniques. In the last part of the thesis, a high-performance, antibiofouling/antibacterial citric acid doped polyaniline based UF membrane was developed. Ensuring sustainability improvement in membrane production in all applications was the main objective of this thesis. By reducing the number of steps in membrane production, the amount of wastewater generated, and toxic waste released during membrane production was minimized, and energy consumption was significantly reduced.Doctoral Thesis Heat and Mass Transfer Characteristics of Adsorbents in Heat Pump and Refrigerator(01. Izmir Institute of Technology, 2023) Gündoğan, Şefika Çağla; Çakıcıoğlu Özkan, Seher FehimeDue to increasing drought, pandemic and climate crisis in recent years, researchers have increased their studies on environmentally friendly energy use. Although there are technological developments in the production of energy from renewable energy sources, the storage of this produced energy is still a problem that awaits a solution. At this point, adsorption heat pumps with high primary energy efficiency come to the fore as a developing technology and attract the attention of researchers. However, low heat transfer properties in the adsorbent bed reduce the performance of adsorption heat pumps and limit their applications. The aim of this thesis was to improve the performance of the adsorption heat pump by increasing the effective thermal conductivity within the adsorbent bed. Two methods have been employed to enhance the effective thermal conductivity. In the first method, which was unconsolidated adsorbent bed design, it was aimed to increase the thermal conductivity of the bed with metal additives with a continuous structure. In the second method, which is known as consolidated bed design, the effective thermal conductivity of zeolite 13X was tried to be enhance with a high conductive material, reduced graphene oxide. In the experimental studies, it was observed that the thermal conductivity increased from 0.12 W/m.K to 0.28 W/m.K in unconsolidated bed design by means of fin-shaped metal additive. In consolidated adsorbent bed design, the effective thermal conductivity of the Graphene/Zeolite 13X (1 wt% Graphene) was determined as 0.1613 W/m.K. In theoretical studies, the effect of thermal conductivity in the temperature, pressure and adsorbate concentration was investigated. The indirect and direct effects of effective thermal conductivity on specific cooling/heating power (SCP/SHP) and coefficient of performance (COP) values were examined. Although the effect of thermal conductivity on COP was ignored in most of the studies in the literature, it was observed that COP increased from 0.01 to 0.10 when thermal conductivity increased from 0.12 W/m.K to 1 W/m.K.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, ÖzgençMetal-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 The Valorization of Various Wastewater for Hydrogen Production by Photocatalytic Oxidation(01. Izmir Institute of Technology, 2021) Orak, Ceren; Yüksel Özşen, AslıHydrogen is a clean, green and sustainable energy and photocatalysis a better approach for hydrogen production from various wastewaters. It was aimed to evolve new hybrid solar-driven catalysts for photocatalytic hydrogen production from various wastewaters. Firstly, catalysts were synthesized. Their characterization study were performed and PL results show that the most promising catalyst was GLFO. The impacts of pH, catalyst loading and light over hydrogen production from SMS were investigated using all synthesized catalysts. The hybrid catalysts show higher efficiency. FFD was created to elucidate the impacts of reaction parameters and graphene content of catalyst had a major impact. To optimize the reaction parameters for all hybrid catalysts, an experimental matrix was created using BBD. The higher hydrogen amounts were observed using GLFO. The same experimental matrix was used to search the effects of reaction parameters over produced hydrogen amounts from sugar beet wastewater using all hybrid catalysts and the highest hydrogen production was observed using GLFO. The observed reaction followed first order reaction model based on TOC removal. Therefore, the degradation of organic pollutants in wastewater streams and hydrogen evolution could simultaneously be achieved. Same experimental matrix was also used for hydrogen evolution from DBU using all hybrid catalysts. Relatively lower hydrogen amounts were obtained so that it was also treated under subcritical conditions. FFD was created to search the impacts of reaction parameters and NaOH concentration and current density had an impact over DBU removal. Based on GC-MS results, the hazardous intermediates did not form during hydrothermal electrolysis.Doctoral Thesis Development of Antifouling Nanofiltration and Antibiofouling Ultrafiltration Polymeric Membranes Using Facile Protocols(Izmir Institute of Technology, 2021) Cihanoğlu, Aydın; Altınkaya, Sacide; Şeker, ErolOne 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) Taykoz, Damla; Bulmuş Zareie, Esma Volga; Tekin, Hüseyin CumhurThe 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.