Dept. of Chemistry - Master's degree
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Item Open Access Analysis of UV induced dehydrochlorinated PVC (With hydroquinone) using direct pyrolysis mass spectrometry (DPMS), TGA, UV/VIS-NIR and FTIR techniques(Bilkent University, 2003) Avcı, ErcanPoly(vinyl chloride) (PVC) degrades easily upon heat and light exposure via loss of HCl. The mechanism of this process is well understood, known as the zip mechanism and the dehydrochlorination results in conjugated segments, polyenes. It is also possible to utilize PVC polymer as an in-situ acid donor since the main degradation product is HCl. Addition of hydroquinone (HQ) into PVC matrix sensitizes the photodehydrochlorination of PVC at 312 nm. In this study the effects of photodehydrochlorination on thermal and material properties of PVC were investigated using DPMS and TGA as well as UV-Vis-NIR and FTIR techniques. In addition, the photodegradation of PVC/PVAc blend, copolymer (PVC-coPVAc) and PVAc were similarly investigated. Dehydrochlorination of the polymers resulting from UV-exposure were also investigated for doping of PANI in blends. HCl evolution behavior of the UV dehydrochlorinated PVC exhibits a characteristic property which is different from the unirradiated ones. Both DPMS and TGA results confirms the sensitization of PVC photodehydrochlorination at 312 nm by hydroquinone (HQ) resulting in a temperature onset that is the lowest (140 oC). HQ assistance upon 312 nm UV exposure is not significantly observed in the copolymer. The low temperature onset of UV-induced copolymer is a promising result to produce longer polyene chains, since polymer backbone starts to decompose after ca. 220 oC, using copolymer might be an alternative to PVC.Item Open Access Autonomous shuttling driven by an oscillating reaction : proof of principle in a cucurbit[7]uril bodipy pseudorotaxane(Bilkent University, 2013) Yaşar, Fatma TubaMiniaturization is a fundamental part of modern technology. Therefore, designing macroscopic machines at molecular level becomes important in terms of mimicking the nature. Despite the numerous molecular machines that were reported in the literature, coupling this design with oscillating reactions to achieve autonomous shuttling was not tried previously. In this thesis, we proposed a novel design for this purpose. Initiating molecular shuttling by oscillating reactions and controlling this shuttling were successfully achieved through a rational design.Oscillating reactions intrigued chemists for a long time, in this work; we propose to utilize oscillations in pH to move the two components of a pseudorotaxane in relation to each other. In a well behaved oscillatory system, the shuttling could be sustained as long as the oscillations continue. This is the first demonstration of a molecular shuttle system in which the ?mobile? component is moving from one station to another in an autonomous fashion. This kind of chemical coupling of an energetically favorable reaction to molecular motion is reminiscent of many biological analogs and therefore highly exciting. Bipyridinium dication substituted BODIPY fluorophore, with a terminal carboxylic acid provides two alternative stations for cucurbit[7]uril (CB7). Changing pH from basic to acidic media results a shuttling of CB7 from one station to another. In addition, the shuttling is accompanied by a change in the emissive properties of the BODIPY dye, which is only observed in the presence of CB7. More striking, it is a demonstration of autonomous shuttling of the pseudorotoxane system in an oscillating pH system.Item Open Access Aza-Nazarov cyclization reactions using anion exchange strategy(Bilkent University, 2019-07) Dönmez, Selin EzgiAlthough Nazarov reaction is a synthetically useful route for the synthesis of five-membered rings, there are a very limited number of studies on its analogous process producing N-heterocycles; aza-Nazarov reaction, and an effective methodology that proceeds under mild conditions has yet to be developed. In consideration of the importance of nitrogen containing heterocyclic compounds in organic and pharmaceutical chemistry, developing a new aza-Nazarov reaction will have the potential to be beneficial in many synthetic applications. In this work, a novel catalytic aza-Nazarov reaction between 3,4-dihydroisoquinolines and α,β-unsaturated acyl chlorides, that can be used for a broad range of substrates, has been developed. By taking advantage of the stabilizing β-silicon effect and the anion exchange strategy, the proposed reaction proceeds under much better conditions with respect to reaction yield, reaction conditions and environmental issues. Our initial efforts focused on the use of achiral anion exchange strategy employing silver trifluoromethanesulfonate (AgOTf) as the anion source to develop a novel aza-Nazarov reaction. To demonstrate that the reaction has a wide substrate scope, the substituents on the starting materials have been changed with electron withdrawing and donating groups. Several attempts have been made to render the developed reaction enantioselective using chiral catalysts, nevertheless asymmetric aza-Nazarov reactions could not be achieved.Item Open Access BaOx(Bilkent University, 2011) Emmez, EmreIn this work, formation anddecomposition pathways of of Ba(NO3)2 on BaOBaO2 /Pt(111) surfaces were investigated at the molecular levelfordifferent BaOBaO2coverages starting from small 2D islands of 0.5 MLE (MLE: monolayer equivalent) to thick multilayers of 10 MLE via temperature-programmed desorption (TPD), and X-ray Photoelectron Spectroscopy (XPS) and Low Energy Electron Diffraction (LEED). BaOxoverlayerswith a surface coverage of ~ 1 MLEreveallong range ordering with (2×2) and/or (1×2) structures while BaOx films with a surface coverage of1.5 MLEyields aBaO(110) termination and thicker films ( ≥ 5 MLE) were observed to be amorphous. Saturation of thick (10 MLE) BaOxoverlayers with NO2 leads to the formation of nitrates. Nitrate thermal decomposition was demonstrated to proceed through nitrite intermediates. In TPD experimentstwo major pathwaysfornitrate decomposition were observed: 1) nitrate decomposition yielding only NO evolutionat ~650 K, and 2) nitrate decomposition withNO + O2evolutionat ~700 K. This multi-step decomposition behavior was explained by BaO2 formation during the first stage. The influence of the BaOxdeposition method on the morphology of the BaOxoverlayers were established: when a thick BaOx layer is prepared using NO2 for Ba oxidation, BaOx overlayer efficiently wets the Pt(111) substrate forming a well-dispersed film. On the other hand, ifa thick BaOx layer is heated in O2 (to 873 K), BaOx overlayer agglomerates into 3D clusters, resulting in the formation of exposed (uncovered) Pt sites. BaOxoverlayers with uncoveredPt sitescan be “cured” by nitration – thermal decomposition procedures. When the BaOx layer coverage is below 2.5 MLE, nitrate decomposition temperature is observed at significantly lower temperatures, demonstrating the catalytic influence of the Pt sites facilitating the nitrate decomposition. It is proposed that initially, Ba(NO3)2 decomposesatthe boundary/peripheralsites of the Pt/BaOx interface, followed by the nitrate decomposition originating from 2D BaOx islands, and eventually from the 3D BaOx agglomerates. Catalytic deactivation of TiO2-promoted NOx-storage reduction (NSR) catalysts due to thermal aging effects was investigated using a BaO/TiO2/Pt(111) model catalyst system. At room temperature, metallic Ba overlayers on TiO2/Pt(111) was found to be very reactive towards oxide ions on TiO2/Pt(111) resulting in the formation of BaOx and partial reduction of TiO2. Ba films adsorbed on TiO2/Pt(111) that are further oxidized in O2 at 523 K lead to BaO and BaO2 surface domains which can efficiently adsorb both NO2 and CO2. Thermal treatment of BaOBaO2/TiO2/Pt(111) surface at T ≥ 300 K leads to a monotonic decrease in the surface Ba/Ti atomic ratio indicating the diffusion of BaO-BaO2 domains into the underlying TiO2 framework. Solid state reactions between BaOx and TiO2 particularly within 473-873K facilitate the formation of BaTiO3/Ba2TiO4/BaxTiyOz overlayers. After oxidation at higher temperatures (T > 873 K), surface becomes Badeficient and the enrichment of the surface with the Ti4+ sites results in a TiO2- terminated surface. Diffusion of BaOx into the TiO2 matrix and the enrichment of the surface with Ti sites drastically suppress the NO2 and CO2 adsorption/storage capacity of the model NOx storage system. These results reveal a direct evidence for the structural changes associated with the thermal deactivation of TiO2-promoted NSR catalysts.Item Open Access BaOx/ Pt(111) AND BaOx/ TiO2/ Pt(111) MODEL CATALYSTS FOR UNDERSTANDING NOx STORAGE-REDUCTION (NSR) CATALYSIS AT THE MOLECULAR LEVEL(Bilkent University, 2011) Emmez, EmreIn this work, formation anddecomposition pathways of of Ba(NO3)2 on BaOBaO2 /Pt(111) surfaces were investigated at the molecular levelfordifferent BaOBaO2coverages starting from small 2D islands of 0.5 MLE (MLE: monolayer equivalent) to thick multilayers of 10 MLE via temperature-programmed desorption (TPD), and X-ray Photoelectron Spectroscopy (XPS) and Low Energy Electron Diffraction (LEED). BaOxoverlayerswith a surface coverage of ~ 1 MLEreveallong range ordering with (2×2) and/or (1×2) structures while BaOx films with a surface coverage of1.5 MLEyields aBaO(110) termination and thicker films ( ≥ 5 MLE) were observed to be amorphous. Saturation of thick (10 MLE) BaOxoverlayers with NO2 leads to the formation of nitrates. Nitrate thermal decomposition was demonstrated to proceed through nitrite intermediates. In TPD experimentstwo major pathwaysfornitrate decomposition were observed: 1) nitrate decomposition yielding only NO evolutionat ~650 K, and 2) nitrate decomposition withNO + O2evolutionat ~700 K. This multi-step decomposition behavior was explained by BaO2 formation during the first stage. The influence of the BaOxdeposition method on the morphology of the BaOxoverlayers were established: when a thick BaOx layer is prepared using NO2 for Ba oxidation, BaOx overlayer efficiently wets the Pt(111) substrate forming a well-dispersed film. On the other hand, ifa thick BaOx layer is heated in O2 (to 873 K), BaOx overlayer agglomerates into 3D clusters, resulting in the formation of exposed (uncovered) Pt sites. BaOxoverlayers with uncoveredPt sitescan be “cured” by nitration – thermal decomposition procedures. When the BaOx layer coverage is below 2.5 MLE, nitrate decomposition temperature is observed at significantly lower temperatures, demonstrating the catalytic influence of the Pt sites facilitating the nitrate decomposition. It is proposed that initially, Ba(NO3)2 decomposesatthe boundary/peripheralsites of the Pt/BaOx interface, followed by the nitrate decomposition originating from 2D BaOx islands, and eventually from the 3D BaOx agglomerates. Catalytic deactivation of TiO2-promoted NOx-storage reduction (NSR) catalysts due to thermal aging effects was investigated using a BaO/TiO2/Pt(111) model catalyst system. At room temperature, metallic Ba overlayers on TiO2/Pt(111) was found to be very reactive towards oxide ions on TiO2/Pt(111) resulting in the formation of BaOx and partial reduction of TiO2. Ba films adsorbed on TiO2/Pt(111) that are further oxidized in O2 at 523 K lead to BaO and BaO2 surface domains which can efficiently adsorb both NO2 and CO2. Thermal treatment of BaOBaO2/TiO2/Pt(111) surface at T ≥ 300 K leads to a monotonic decrease in the surface Ba/Ti atomic ratio indicating the diffusion of BaO-BaO2 domains into the underlying TiO2 framework. Solid state reactions between BaOx and TiO2 particularly within 473-873K facilitate the formation of BaTiO3/Ba2TiO4/BaxTiyOz overlayers. After oxidation at higher temperatures (T > 873 K), surface becomes Badeficient and the enrichment of the surface with the Ti4+ sites results in a TiO2- terminated surface. Diffusion of BaOx into the TiO2 matrix and the enrichment of the surface with Ti sites drastically suppress the NO2 and CO2 adsorption/storage capacity of the model NOx storage system. These results reveal a direct evidence for the structural changes associated with the thermal deactivation of TiO2-promoted NSR catalysts.Item Embargo Bimetallic hydroxide catalysts for aerobic C-H activation(Bilkent University, 2024-01) Erdivan, BeyzanurThe increasing interest in the oxidation of sp3 C-H and O-H bonds has garnered tremendous attention due to its potential for facile production of oxygenated organics. Precious metal-free bimetallic hydroxide-based materials are commonly employed in various applications such as batteries and photocatalysts. However, their prospects in C-H activation reactions have been poorly explored. This research focuses on the development and evaluation of a bimetallic Fe-Mn hydroxide catalyst for aerobic C-H activation and O-H oxidation reactions without the need for an initiator. The Fe-Mn hydroxide catalyst was synthesized and carefully optimized to enhance its catalytic efficiency in the direct oxygenation of a wide scope of alkylarene compounds through C-H functionalization and oxidation of benzylic alcohols. A series of Fe-Mn bimetal hydroxides with different Fe/Mn ratios were synthesized using a customized chemical co-precipitation method. These catalysts were then tested for the catalytic oxidation of fluorene to fluorenone using molecular oxygen as the sole oxidant, with the Fe0.6Mn0.4(OH)y-12S catalyst demonstrating the best performance. Under mild reaction conditions, the catalyst exhibited remarkable performance in activating C-H bonds using molecular oxygen as the oxidant. Various substrates, including alkylarenes and alcohols, were investigated, consistently yielding high yields of oxygenated products with minimal catalyst loadings. XRD, XPS, XANES, ICP-MS, BET, and TGA were employed to gain insights into the structural features of the catalyst. Our findings indicate that the following structural properties of the optimized Fe0.6Mn0.4(OH)y-12S catalyst could be responsible for the currently observed enhanced catalytic reactivity: i) unique Mn oxidation state (ca. Mn2.6+), ii) Fe cationic sites containing a mixture of Fe2+ and Fe3+ species, where Fe3+ species are the dominating species, iii)realtively low specific surface area of 68 m2/g, iv) relatively disordered and defective crystal structure comprised of bimetallic hydroxides as well as additional oxide/oxyhydroxide phases, v) residual Na+ surface species enabling electronic promotion of the cationic active sites via electron donation.Item Open Access Bio-inspired paper plant robots: artificial heliotropism and nyctinasty through transpiration(Bilkent University, 2019-08) Cezan, Süleyman DorukSelf-regulation is a fundamental feature of all living systems, which maintains their metabolic activities through biochemical feedback loops. Those feedback loops respond to environmental stimuli, and therefore the organism displays ‘embodied intelligence’. Despite the complexity of these feedback loops, using them as a source of inspiration can open new endeavors in soft robotics to design self-regulating systems, and ultimately to fuse embodied intelligence into soft robots. Here we show some simple systems, in which plant-inspired soft robots display heliotropism (tracking the sun) and nyctinasty (opening and closing its leaves) through material feedback and artificial transpiration for self-regulation – all being examples of embodiment of intelligence. First, materials feedback is adapted to a hard robotic system behaving similar to a soft robot, displaying heliotropism and nyctinasty by using the phase transition of shape memory alloy springs. Then, artificial transpiration is integrated into a soft robotic system, using swelling/deswelling of hydrogels on the paper body by using origami/kirigami strategies. Both material and transpiration feedback involve stabilization with cycles of traction and contraction (of shape memory alloys, or hydrogels) events that keep the robots at a metastable state, maximizing of solar flux on the leaves (decorated with solar panels) for higher efficiencies of harvesting light. Moreover, the feedback mechanism of the hydrogel-based system can be advanced by using hybrid hydrogels (e.g. an addition of thermoresponsive hydrogels), or doping the gel with light-absorbing chemicals, or altering the geometrical design of the systems. Finally, achieving self-regulation in soft robots through material/transpiration feedback is important to attain the embodiment of intelligence in them, and this may have implications extending from energy efficiency to adaptability in autonomous soft robots.Item Open Access Brønsted acid-catalyzed inverse electron-demand diels-alder reactions of 1,2-diazines(Bilkent University, 2023-09) Korkmaz, Hatice SeherThe discovery of Diels-Alder reaction by Otto Diels and Kurt Alder in 1928 marked an important development in synthetic organic chemistry. This [4+2] cycloaddition reaction has been used in a variety of ways over the years, from natural product synthesis to medicinal chemistry. The process produces derivatives of cyclohexane by the coordinated addition of a conjugated diene and a dienophile. As a subclass of Diels-Alder reactions, inverse electron-demand Diels-Alder (IEDDA) reactions are covered in this thesis, along with their intricate mechanisms and applications. IEDDA cycloaddition reactions have become more well-known recently, especially in the fields of chemical biology, bio-orthogonal reactions and the synthesis of complex molecules. These reactions generally have excellent regio- and stereoselectivity and they occur between electron-poor dienes and electron-rich dienophiles. They have been crucial in the synthesis of bioactive substances with potential use for the cancer treatment, such as halenaquinone and rhodexin A. Catalysts have become an effective means of promoting IEDDA reactions in the search for milder reaction conditions and higher yield. To modify the energy levels of dienes and increase reactivity, Brønsted acid catalyst has been used in this project. This study involves the investigation of pyridinium salts as Brønsted acid catalyst intended to reduce the LUMO energy levels of 1,2-diazines. The goal is to make diazines more reactive in IEDDA reactions, creating new pathways for the synthesis of a variety of complex molecules. By bridging the gap between difficult reaction conditions and effective IEDDA reactions, this project aims to increase the usefulness of this potent synthetic method in contemporary organic chemistry.Item Open Access Catalytic metal hydroxide nanostructures: aerobic C-H activation and catalytic low temperature carbon monoxide oxidation by NixMn(1-x)(OH)2(Bilkent University, 2021-02) Sika-Nartey, Abel TettehMetal hydroxides and mixed metal hydroxides have been frequently utilized in diverse applications such as battery technologies, electrocatalysis, electrosynthesis, photocatalysis, supercapacitors, electrochromic devices, and electrochemical sensors. Yet, precious metal-free hydroxides have not been utilized to their full potential in the field of catalytic aerobic C-H activation and catalytic low-temperature CO oxidation. In this work, we demonstrate that upon careful optimization of catalyst synthesis protocols, a novel catalytic architecture is achieved in the form of Ni0.6Mn0.4(OH)2 revealing remarkable catalytic performance in the aerobic oxidation of alkylarenes, particularly in the aerobic oxidation of xanthene to xanthone. This optimized catalyst also shows superior catalytic activity in low-temperature CO (g) oxidation. We also present an efficient catalytic regeneration protocol, which can redeem the full initial activity of the carbon-poisoned spent catalyst in xanthene oxidation. Catalytic functionality of this novel nanomaterial architecture is also examined in detail in light of comprehensive characterization experiments including ATR-IR, XRD, BET-SSA, TGA, TEM, EDX and XPS measurements.Item Open Access Ceria promoted NOx storage and reduction materials(Bilkent University, 2011) Say, ZaferIn the current work, the effect of CeO2 promotion on the NOx storage materials and NOx storage-reduction (NSR) catalysts is studied. Synthesized materials were prepared using different baria and ceria loadings in order to investigate the influence of the surface composition on the NOx storage process. Synthesized materials were also thermally treated in the temperature range within 300 - 1273 K to mimic the thermal aging effects on the material structure. Structural properties of the synthesized materials were investigated via spectroscopic and diffraction techniques such as Raman spectroscopy, X-ray diffraction (XRD), and BET (Brunauer, Emmett, ve Teller) surface area analysis. These ex-situ characterization studies revealed that materials containing Pt showed indications of sintering after thermal treatment at elevated temperatures where Pt sites grew in size and were partially covered by BaO domains. Pt addition to the BaO/Al2O3 system facilitated the formation of the undesired BaAl2O4 phase, particularly at high baria loadings. Decomposition of the Ba(NO3)2 species took place at lower temperatures for Pt containing materials. An indication for a strong-metal-support interaction (SMSI) between Pt and CeO2 sites was observed in Raman spectroscopic data, resulting in the formation of a new mixed oxide phase on the surface. BET results indicated that the specific surface area (SSA) of the synthesized materials monotonically decreased with increasing temperature and increasing BaO and CeO2 loadings. The behavior of the synthesized materials in NOx and SOx adsorption experiments were also investigated via temperature programmed desorption (TPD) and in-situ Fourier transform infrared (FTIR) spectroscopy. Ceria promotion had no significant influence on the nature of the adsorbed nitrate species and the NOx uptake ability of the alumina support material. On the other hand, addition of Pt to CeO2/Al2O3 binary and BaO/CeO2/Al2O3 ternary systems was observed to enhance the NOx storage. For the ternary mixed oxide NOx storage systems (BaO/CeO2/Al2O3), increasing BaO or CeO2 loadings results in a decrease in the specific surface area values, which in turn leads to decreasing NOx uptake. SO2 (g) + O2 (g) interaction with a selected set of samples were also investigated via in-situ FTIR spectroscopy. These experiments reveal that ceria promotion and platinum addition assisted the formation of surface sulfate species. Furthermore, the presence of ceria also resulted in a decrease in the thermal stability of sulfates and enabled easier regeneration.Item Open Access Charge dissipation mechanism of low-cost antistatic additive lignin in contact charged polymers(Bilkent University, 2019-07) Özel, MertcanContact electrification (C.E.), a phenomenon studied for millennia, develops contact charges on material surfaces, when two materials are contacted and then separated. Accumulation of contact charges and their uncontrolled sudden discharges on dielectric polymers pose major drawbacks in industries i.e. pharmaceutical, (micro)electronics, and space, causing million-dollar losses annually. The overall mechanism of C.E. is unclear until now, however, recent efforts have proven that chemical bond-breakages on polymer surfaces result in mechanoions – which are indeed the contact charges on the surfaces. These studies also showed that removing mechanoradicals (co-formed upon bond-breaking) by molecular radical scavengers destabilizes the mechanoions (charges) and render the doped polymer material antistatic. This method of static charge mitigation has an advantage over the conventional methods (e.g. doping with metals, carbon powder, conductive polymers, or surface humidity enhancers) because it is not based on an increase in surface conductance and smaller doping concentrations are needed to achieve antistatic behavior. However, currently used molecular radical scavenger doping is generally not cost effective method to be upscaled for industrial use. Lignin; however, is a “low-cost” material (the second most abundant polymer on earth, a by-product of paper production) that can act as a radical scavenger. In this thesis work, lignin was extracted from some examples of both hard and softwood. Firstly, it was verified that lignin doping in low concentrations (1 – 5% w/w) reduce the contact charge accumulation on common polymers such as on a crosslinked elastomer polydimethylsiloxane, and on thermoplastics polypropylene, polyethylene, polylactic acid, and polystyrene. Then, the mechanism of the observed charge dissipation was discussed in the light of the results obtained from surface conductance of polymers upon doping, 31P NMR and solid state 13C-NMR spectroscopy, total phenol content, and the reacted number of radicals before and after grinding - which was shown essential to get homogeneous doping- of lignin. The results pointed out a mechanism involving a radical scavenging activity without any change in the surface conductance of the material, similar to that with molecular radicals. The understanding of lignin’s charge dissipation mechanism will be helpful in industrial utilization of lignin as an antistatic additive and in assessment of the limitations of this utilization.Item Open Access Chemical and mechanical control of liesegang patterns in polyacrylamide hydrogels(Bilkent University, 2018-07) Ashirov, RahymSelf-assembly of molecular components have attracted attention of scientific community in the past decades because of their great potential in designing functional devices in material science. Formed by simultaneous diffusion and precipitation reaction of co-precipitating chemicals in gel media, Liesegang patterns (LPs) are one of the examples of spontaneous pattern formation. LPs have been an attractive topic since their discovery in 1896, due to their wide occurrence in nature and potential applications in sensors, surface sciences, MEMS, bioengineering and microfluidics and fabrication of microstructured materials. Yet, mystery behind formation mechanism of LPs has not been completely solved. More parameters and conditions are needed to be investigated to understand the mechanism. In this study, we show that formation of Liesegang patterns in polyacrylamide hydrogels can be chemically and mechanically controlled. Firstly, we changed the chemical composition of the hydrogels and monitored the changes in the LPs formed at different locations. Then, we demonstrated that mechanical stress can alter LP formation both in terms of geometry of the rings and of their ‘appearance times’. Without any mechanical input, in (pseudo-) 2D gels, LPs form in circular shape. However, when mechanical stress is applied on gels, LPs appear as concentric ovals, the aspect ratio of which increases as applied mechanical stress increases. In this thesis, for the first time in the literature, we have provided mechanical manipulation of LPs. The time-dependent formation of the patterns and their significant alteration by mechanical input can help us build elastic deformation sensor through the visible patterns.Item Open Access Chemical characterization and provenance studies of archeological samples(Bilkent University, 2003) Türkmen, Işık RızaData that is collected by chemical analyses of the archeological samples can be used to find out the the raw materials used and the techniques practiced in the ancient pottery production. In addition, provenance studies of archeological samples that are commercially important may give an idea on the commercial relationships between the past civilizations. This study was conducted to investigate the chemical compositions and provenance of the amphora samples that are found around Sinop and Heraclea Pontica (Black Sea Coast) in Turkey, Ibn-Hani (Eastern Mediterranean Coast) in Syria, Tanais and Gorgippia on Northern Black Sea region of Russia. Some amphorae, which are morphologically similar to those of Colchian amphorae, but having apparently distinctive clay properties, are called Pseudo-Colchian, and they were also analyzed during the studies. The mineral compositions of the samples were found out by powder X-Ray Diffraction analyses, and the elemental compositions were sought by X-Ray Fluorescence spectroscopy. Principal component analysis and cluster analysis are applied to the data collected from XRF measurements for the provenance classification of the samples. The results obtained from both statistical methods complemented each others and were in good agreement. According to the results of this study, the pink clay, red clay and white clay amphorae from Sinop are all found to be composed of the minerals quartz, feldspars, pyroxenes, calcite and hematite, but varying in amounts with respect to type and color. Considering the mineralogical compositions, it is proposed that the average baking temperature of the red clay amphorae is around 800 – 850 o C whereas it is around 950 o C for the white clay ones. The red color observed for the red clay Sinopean amphorae was attributed to the presence of hematite minerals. On the other hand white color was attributed to the formation of mineral phases such as pyroxenes, throughout the chemical reactions that take place in the clay matrix at higher baking tempertures and low oxidation environments for the white clay Sinopean amphorae. In provenance classification of the samples, it was found that the separations between the samples occur mainly due to variations in the concentration of elements Ca, Fe, Ti, Ni, Rb and Sr. White clay amphorae from Antioch and Ibn Hani, and the red clay carrot type amphora from Tanais are found to be the Sinopean production. On the other hand, the white clay amphorae from Tanais was found to be more similar to the ones from Heraclea Pontica and different from those of Sinop. The colchian amphorae from Gorgippia and Pseudo-Colchian amphorae were found to represent typical differences from all other samples, but also from each others.Item Open Access Chemical characterization of Sinopean archaeological common ware(Bilkent University, 2004) Özal, Tuğba ArzuChemical characterization of archaeological common wares is important in order to make quantitative explanations about history and trade relations of nations. Chemistry uses a microscopic point of view by applying spectroscopic methods rather than macroscopic studies that archaeologists usually deal in the structural analysis. The present study is done on the common ware samples which were made of raw clays from Demirci, Sinop, Black Sea Coast of Turkey, because of the geopolitical importance of this region having trade routes. Elemental and mineralogical analyses of the clay-originated common ware samples found in the archaeological excavations and of the clay taken from Demirci region, which locates at almost 15 km southern of Sinop, were made. While the elemental compositions of the samples were obtained by the spectroscopic method, X-Ray Fluorescence (XRF), the mineral structures were investigated by Powder XRay Diffraction (PXRD) and Fourier Transform Infra Red (FT-IR) spectroscopic method. Furthermore, the characteristic reactions (dehydroxylation, decomposition, transformation) that the clays experienced between the temperatures 50 and 1000 o C were determined by Thermal Gravimetric Analysis (TGA). Characterizations of the Sinopean samples were made and the similarity and differences between other samples from different regions were investigated. Besides the provenance characterization, the distinctions between the production and firing techniques were observed. In addition to the experimental studies, chemometric techniques using statistical methods such as the standard clustering method and principal component analysis (PCA) was also applied to identify the groupings in the set of samples. As a result of this study, it is observed that the raw clays and ceramic samples have minerals of montmorillonite, quartz, feldspars, pyroxene, calcite and hematite at different amounts. From the mineralogical and elemental data, it is concluded that the color variations are resulted from the calcium element occurring in pyroxene mineral. In the light colored samples, amount of this element and mineral is high whereas it is low in red colored ones. From the interpretation of elemental data by statistical methods, it is observed that a classification among the Demirci samples is possible according to the function of the pottery. In addition, classification among ceramics from two different regions is possible by the interpretation of chemical analysis, even though the ceramics have the same morphological properties of the same period.Item Open Access Chemical modulation of singlet oxygen generation rates in thermal endoperoxide decomposition & novel fluorescent sensors for hyperphosporylated tau proteins(Bilkent University, 2016-05) Kaya, CansuChemical control over singlet oxygen generation is an open to improvement because of the importance of this reactive species in biological systems. In the first project, we aimed to synthesize a silylated 1,4-dimethylnaphthalene endoperoxide derivative which is expected to release singlet oxygen on thermolysis at a relatively slow rate at room temperature. Upon the deprotection of the silyl units with fluorine ions, it is expected it to release singlet oxygen at a much higher rate, giving rise to a control over the release of the product. The absorption and the fluorescence measurement with a trap molecule which consumes the generated singlet oxygen reveals promising results for the future work for the control of singlet oxygen generation rates. In the second part of this thesis, we focused on the synthesis of a novel fluorescent sensor of a BODIPY derivative which is capable of sensing Zinc cations. The zinc complex is also expected to have a further usage for the sensing of hyperphosphorylated tau proteins, which are commonly produced in the brains of people with Alzheimer’s disease. With this, it has a potential usage in the field of early detection of Alzheimer’s disease.Item Open Access Chemical vapor deposition of boron nitride nanotubes(Bilkent University, 2013) Çiftçi, Niyazi OkanSince ancient times materials that are available and used by people constitute indispensable constituent parts of world history. The historical ages are named after the materials which paved an irrevocable way to this stream and revolutionize the progress of history by changing the rhythm of anthropological breakthrough irreversibly. People have used these materials either directly borrowing from nature or by transforming those that are given. As we approach to modern society two methods namely a top-down method using transmission of experiences of before generations conventionally and bottom-up method by application of modern science and technology to understand subtleties of materials and engineering them for the specific goals. Boron nitride nanotubes are one class of these materials having superior properties to the conventional ones. High strength, electrically insulator property, controllable wide band gap and high oxidation resistance as compared to carbon nanotubes put them to the first ranks for the design of the future devices for our modern society. Hence a simple and inexpensive way of production of this kind of materials is utmost importance. For this in this thesis an inexpensive and a very practical way of BNNTs production is elucidated. The reactants boron (B), iron (III) oxide (Fe2O3) and magnesium oxide (MgO) are used as solid precursors. A CVD furnace reaching up till 1200 oC with a special design of added concentric quartz tubes equipped with NH3 and Argon gas served as reaction chamber.Item Open Access CO2 activation on MnOx /Pd(111) model catalyst(Bilkent University, 2022-07) Anıl, ArcaCO2 is an atmospheric pollutant (i.e., a greenhouse gas) and it can be converted into valuable chemicals such as methanol, methane, and formic acid. However, CO2 reduction is a challenging process due to the thermodynamic stability of CO2. In this work, we focus on the activation of CO2 by using an atomically well-defined MnOx/Pd(111) planar model catalyst. Pd(111) surface can dissociatively adsorb hydrogen molecules, but CO2 does not strongly bind to the Pd(111) surface. On the other hand, MnOx nano-structures can facilitate the activation of CO2 due to the presence of acid and base sites on the metal oxide surface. Therefore, MnOx/Pd(111) was chosen as a model catalyst to investigate catalytic CO2 activation. A multifunctional ultra-high vacuum system with quadrupole mass spectrometer (QMS), X-ray photoelectron spectrometer (XPS), and low energy electron diffraction (LEED) was used to perform the experiments. Manganese thin film growth mechanism on Pd(111) surface was determined by using XPS. Manganese was evaporated on Pd(111) substrate at two different temperatures (i.e., 85 K and 300 K). Formation of products after the dosing of the reactants on the MnOx/Pd(111) surface was examined via temperature programmed desorption (TPD). For both cases, formed manganese oxide thin film was investigated by using XPS to estimate the relative, Mn0, Mn2+ and Mn3+ surface concentrations. Prepared manganese film on Pd(111) at 300 K could activate CO2 to CO, which is a valuable chemical for the chemical industry. To prepare smaller clusters, manganese was evaporated on the Pd(111) single crystal surface at 85 K. At moderate manganese coverage, carbonate CO32- formation was detected on the MnOx/Pd(111) interfacial sites.Item Open Access CoFe prussian blue coordination compounds incorporating metallopolymers: Investigation of electrocatalytic water oxidation activities(Bilkent University, 2016-02) Demirkıran, MerveHydrogen economy, which depends on water and sunlight as energy source, needs to be implemented as an alternative to carbon based economy. For the development of a technology that incorporates hydrogen energy to our daily lives, it is required to split the water with the help of an efficient water oxidation catalyst. CoFe Prussian Blue analogues have recently been investigated as heterogeneous water oxidation catalysts. Even though they exhibit they exhibit high electrocatalytic activity in addition to superior stability in both acidic and neutral media low current densities were obtained with CoFe PB modified FTO electrodes due to their low surface coverage. This challenge could be overcome by developing novel synthetic methods that will enforce the formation of amorphous CoFe Prussian Blue analogues. Herein this thesis, pentacyanoferrate based metallopolymers were used as precursors to prepare amorphous Co-Fe analogues. The project focuses on the improving surface concentration by using Poly 4-vinyl pyridine (P4VP) not only as a capping ligand connected to pentacyanoferrate complexes but also as a surfactant to prevent the formation of long-range ordering between Co-Fe networks. Surface concentration was improved approximately seven fold, which resulted in an increase in the catalytic activity. A current density of 1 mA.cm-2 was obtained only at η = 510 mV while the same current density could be obtained only at higher overpotentials (>600 mV) with the previously studied Prussian Blue analogues. The stability of CoFe-PVP coated FTO electrodes were investigated before and after the electrocatalytic process using Infrared, XPS, and EDX studies. The results of this study indicate that the rich and diverse chemistry of pentacyanoferrates make them potential candidates for application in heterogeneous water oxidation catalysis.Item Open Access Conjugated polymer nanoparticles for biomedical applications including bioimaging and drug delivery(Bilkent University, 2013) Ünal, ÖzlemItem Open Access Conjugated polymers based on polyfluorene derivatives and polypyrrole(Bilkent University, 2007) Koldemir, ÜnsalIn this thesis, a series of polyfluorene based copolymers have been prepared via Suzuki Coupling for use in light emitting diodes (LEDs). Polyfluorene based polymers are synthesized from different monomers. These polymers are characterized with spectroscopic techniques including FT-IR, UV-VIS, Fluorescence and 1H, 13C NMR. Conjugated polymers are attractive chemical structures inherently allowing charge transport. However, in the solid state, conjugated polymers lack stability and form aggregates. To overcome this problem, conjugated polymers can be converted to insulated molecular wires. This can be achieved by separation of the conjugated polymer chains by a macrocycle. In this study, encapsulation of conjugated polymers is tried with two methods. First method is to encapsulate the polymer main chain by macrocycles. Polypyrrole based polypseudorotaxane is prepared in this way. Pyrrole is complexed with the cucurbit[6]uril (CB(6)) and following chemical oxidation by FeCl3 in acidic medium yields the desired polypseudorotaxane. Spectroscopic investigations such as FT-IR, UV-VIS, Fluorescence and 1H-NMR confirm the formation of polypyrrole based polypseudorotaxane. The second method involves the rotaxanation of the polymer side chains. For this purpose, fluorene based monomers are chosen because the 9th position of fluorene can be easily functionalized. After attaching suitable groups to the 9th position of fluorene, the rotaxane formation was attempted via 1,3 dipolar cycloaddition in the presence of CB(6). A white light emitting diode is prepared using a hybrid inorganic and organic material based system. Prepared conjugated polymers were used in white light generation. Good results are obtained with high CRI indices. Also the thermal stability of the conjugated polymers is studied by FT-IR, UV-VIS and Fluorescence spectroscopic techniques under heat exposure.