Theses supervised by Doç. Dr. Uğur Ünal
13 theses · Gazi University, Koç University
20. yüzyıl başlarında Bursa'da eğitim öğretim faaliyetleri
?20. Yüzyıl Başlarında Bursa'da Eğitim Öğretim Faaliyetleri? adlı tezimizin amacı, Osmanlı Devleti'nin 19. yüzyıldaki modernleşme sürecinde, eğitim öğretim alanında Bursa'nın yerini tespit etmek ve bu konuda istatistikî bilgiler vermektir. Çalışmamız 20. yüzyılın başı ile sınırlandırılmıştır. Tezimizin ana kaynağını Hudâvendigâr Vilâyeti Salnâmeleri, Maârif Salnâmeleri ve Devlet Salnâmeleri oluşturmaktadır. Salnâmelerden elde edilen bilgiler, arşiv belgeleri ve telîf eserlerle takviye edilerek desteklenmeye çalışılmıştır. 20. yüzyıl başlarında Bursa Sancağı'nda (yıllara göre değişmekle birlikte); 1 Vilâyet Maârif İdaresi ve merkeze bağlı Mudanya, Mihaliç, Adranos, Kirmasti, Gemlik ve Pazarköy kazalarında birer maârif şubesi, 654'ü eski usûl 33'ü yeni usûlde olmak üzere toplam 687 ibtidâî mektebi, Bursa Sancağı ile bağlı kaza ve bucaklarda 9 Rüşdiye, 1 İnas (kız) Rüşdiyesi, 1 Mülkî İdâdî, 1 Askerî İdâdî, 1 Dârülmuallimîn, 33 Medrese, 1 Sanâyi Mektebi, 1 Zirâat Mektebi, 1 Harîr Dârüttalîmi, 1 Harîr Dârüttahsîli, 1 Hadîka-i İrfân ile gayrimüslimlere ait 3 İdâdî, 36 Rüşdiye ve 151 İbtidâiye mektebi bulunmaktadır. Ayrıca 1 Amerikan Mektebi, 3 Fransız Mektebi ve 1 de Rus Mektebi mevcuttur.Anahtar Sözcükler:1. Bursa2. Eğitim Öğretim3. Mektep4. Hudâvendigâr5. İstatistik
I. Meşrutiyet Dönemi Makedonya'da Bulgar çete faaliyetleri
Tarih boyunca, bir çok milletin bir biriyle mücadele sebebi ve alanı olan Makedonya, bu mücadeleler sonucu muhtelif devletlerin yönetimine geçmiş bir coğrafya olması hasebiyle büyük önem arz etmektedir. Bu sebeple, sayısız göçlere ve savaşlara sahne olması; ayrıca çeşitli etnik unsurların bu bölge üzerinde hak iddia etmesi, ortaya değişik Makedonya tanımlarının çıkmasına sebep olmuştur. Siyasi sınırlarının yanında, etnik ve dini yapısı da karışık olan bu coğrafya, gerek siyasi gerekse etnik olarak yamalı bohçayı andırır tarzdadır. Makedonya'daki bu siyasi ve etnik durum, milliyetçilik akımının etkisi ile daha da karmaşık bir hal almıştır. Makedonya'daki etnik unsurların her biri, 18. Yüzyılda başlayan ?milliyetçilik? akımının etkisine kapılarak, mezkur bölgeyi kendi topraklarına katmak için büyük bir mücadeleye girişmişlerdir. Bu mücadele, tarihte ?Makedonya Sorunu? olarak addedilmiştir. Makedonya'da hak iddiasında bulunan ulusların her biri, Makedonya'da komiteler kurarak Osmanlı Devleti egemenliğine karşı olduklarını ortaya koymakla kalmamış fiili mücadeleye geçmişlerdir. Komitelerin bu fiiliyatı çeşitli silahlarla ve acımasızca yapmaya başlaması, Makedonya bölgesindeki karışıklığı daha da arttırmıştır. Özellikle de bu çalışmanın özünü teşkil eden ?Bulgar komite ve çetelerinin faaliyetleri?, diğerlerine nazaran Osmanlı Devleti'ni, daha zor duruma düşürmüştür. Çalışmanın kapsamı, I. Meşrutiyet döneminde Bulgar komite ve çete faaliyetleri olarak belirlenmiştir. Berlin Antlaşması'yla başlayan bu süreçte Bulgaristan, Büyük Bulgaristan hayalini gerçekleştirmek için önce Şarkî Rumeli Vilayeti'ni ilhak etmiş, sonra da Makedonya'yı topraklarına dâhil etmek için faaliyetlerini yoğunlaştırmıştır. Bu durum, çete faaliyetleri sebebiyle, yapılması öngörülen ıslahatların da uygulanmasını zorlaştırmıştır. Zaten Bulgarların amacı, ıslahın gerçekleşmesi değil asayişin daha da bozulmasını temin ederek ?Bölgede can güvenliği yok; Osmanlı Devleti gerekenleri yapmıyor? telkini ile Avrupa'nın bölgeye müdahalesini sağlamaktı. Osmanlı Devleti, Makedonya'daki çete faaliyetlerine karşı sıkı önlemler almıştır. Ancak bölgede Bulgar çetelerinin terör eylemleri ve Avrupa'nın bitmek bilmeyen müdahaleleri ile Osmanlı Devleti'nin maddi anlamdaki yetersizlikleri, alınan tüm tedbirlerin sonuçsuz kalmasına neden olmuştur.Anahtar Kelimeler:1.Makedonya Meselesi,2.Bulgar komiteleri,3.Bulgar çeteleri,4.Bulgar eşkiyaları,5.Osmanlı Devleti.
12. sınıf ?Çağdaş Türk ve Dünya Tarihi? ders kitabının öğretmen ve öğrenci görüşleri ışığında değerlendirilmesi
Tarih öğretimi ve özellikle tarih ders kitapları, toplumsal ve akademik alanda son yıllarda kapsamlı eleştirilere ve tartışmalara konu olmuştur. Ülkemizde tarih öğretimi alanında yapılan önemli gelişmelerden biride 2008 yılında hazırlanan Orta Öğretim Çağdaş Türk ve Dünya Tarihi Dersi Öğretim Programıdır. Bu araştırmanın genel amacı da lise programlarına yeni giren 12. sınıf ?Çağdaş Türk ve Dünya Tarihi? ders kitabının niteliğini ve bu konuda tarih öğretmenlerinin ve 12. sınıf öğrencilerinin görüşlerini ortaya koymaktır.Araştırma kapsamında literatür taraması yapılmış ve ders kitaplarının eğitim-öğretim açısından önemine değinilmiş ve ayrıca tarih öğretimi hakkında bilgi verilmiştir. Bu araştırma, Çağdaş Türk ve Dünya Tarihi ders kitabı ile ilgili tarih öğretmenlerinin ve okullarımızda bu dersi alan 12. sınıf öğrencilerinin görüşlerini tespit etmeye yöneliktir. Araştırma kapsamında öğretmen ve öğrencilere anket formu uygulanmıştır. Araştırmamız bu yönüyle tarama modeline uygun olarak yapılmıştır. Yapılan anket çalışması sonucunda; öğretmen ve öğrenci görüşlerinin birbirinden farklı olduğunu anlaşılmaktadır. Öğretmenler ders kitabının öğrenci seviyesine uygun ve görsellerinin yeterli olduğunu düşünürken, kitabın öğrencide merak uyandırmadığını ve dersi sevdirmekten uzak olduğunu belirtmişlerdir. Öğrenciler ise ders kitabının çok fazla eksiği olduğu yönünde fikir belirtmişlerdir. ?Çağdaş Türk ve Dünya Tarihi? ders kitabının ders için yeterli olmadığını, konu anlatımının ilgi çekmediğini ve görsellerin merak uyandırıcı nitelikte olmadığını söylerler. Yapılan araştırmadan elde edilen sonuçlar doğrultusunda 12.sınıf ?Çağdaş Türk ve Dünya Tarihi? ders kitabının öğretmen ve öğrenci görüşü ışığında olumlu ? olumsuz yönleri tespit edilerek önerilerde bulunulmuştur.Anahtar Kelimeler: Tarih, ders kitabı, tarih öğretimi.
Ortaöğretim 10. sınıf tarih ders kitabının öğrenci görüşlerine göre değerlendirilmesi
Bu araştırmada, ortaöğretim 10. sınıf tarih ders kitabının, öğrenci görüşleri doğrultusunda genel bir değerlendirmesini yapmak; MEB tarafından yayımlanan 10. sınıf ders kitabının eksik ve hatalı yönleri belirlenerek daha etkin, işlevsel ve verimli olabilecek ders kitaplarının hazırlanmasına katkıda bulunmak amaçlanmıştır.Araştırmada betimsel yöntem kullanılmıştır. Veri toplama aracı olarak ders kitabını değerlendirmeye yönelik bir öğrenci anketi kullanılmıştır. Araştırmanın çalışma evreni, Ankara ili Yenimahalle İlçesi'ndeki Türk Telekom Mehmet Kaplan Sosyal Bilimler Lisesi, Gazi Çiftliği Lisesi ve Alparslan Lisesi'nde öğrenim gören 10. sınıf öğrencilerinden seçilen 250 kişi ile oluşturulmuştur. Verilerin analizinde Excel ve SPSS programlarından yararlanılmıştır. Anketlerin güvenirliği Cronbach Alpha katsayısı hesaplanarak bulunmuştur. Araştırma sonucunda elde edilen bulgulara göre MEB tarafından yayımlanan Talim ve Terbiye Kurulu tarafından incelenen ve okunabilirliğine yönelik izin verilen 10. sınıf Tarih ders kitabının önemli eksikliklerinin olduğu ifade edilmektedir. Fiziksel özellikleri öğrencide okuma isteği uyandırmamakta, baskı hatlarına rastlanmakta, sağlam ve kullanışlı bir kitap özelliği taşımamaktadır. Ders kitabında kullanılan görsel ve yazılı materyaller de araştırmaya katılan öğrenciler tarafından gerek nicelik, gerek çeşitlilik ve amaca hizmet etme konusunda yetersiz olarak değerlendirilmektedir. Öğrencilerin tarih 10. sınıf ders kitabının içeriğine yönelik görüşleri de genelde olumsuz bir yapıdadır. Öğrencilerin çoğunluğu ders kitabı içeriğinin beklentilerini karşılamadığı konusunda hemfikirdir. Tarih 10. sınıf ders kitabının Türkçemizin dil, imla ve anlatım özelliklerine de bütünüyle uygun olduğu söylenemez. Ayrıca ders kitabının ölçme ve değerlendirme boyutu da öğrenciler tarafından genelde sorunlu görülmektedir. Öğrencilerin ders kitabını değerlendirmeye yönelik görüşlerinin cinsiyet, öğrenim görülen okul, anne ve baba mesleği, anne ve baba eğitim düzeyine göre farklılaşmaları da incelenmiş bu değişkenlerin çoğunun öğrencilerin bu konudaki görüşlerinde farklılığa neden olduğu görülmüştür. Araştırmamızın içeriğini oluşturan tarih ders kitapları öğrenci açısından bekleneni verememektedir ve çağdaş tarih ders kitapları ölçütlerini tam olarak karşılayacak nitelikte değildir. Ayrıca anlatımda çoklu yaklaşımdan ziyade tek doğrunun hâkim olduğu, öğrencilerin tarihsel eleştiri ve düşünsel yeteneklerinin zayıf bırakıldığı anlaşılmaktadır. Ders kitaplarının önemli bir eğitim ve öğretim aracı olarak kabul edildiği ülkemizde daha nitelikli, daha kaliteli kitaplar yazılması hem öğrencinin derse ilgisini arttıracak hem de eğitimdeki başarıyı olumlu yönde etkileyecektir. Bu bilgiler doğrultusunda tarih öğretmenleri, ders kitabı yazarları, yayınevleri ile MEB ve alanda araştırma yapacaklara önerilerde bulunulmuştur.Anahtar kelimeler: Tarih öğretimi, ders kitabı, öğrenci görüşleri
N-deposited carbon supported FeNi alloys as electrocatalysts for oxygen evolution reaction
Water electrolysis is a renewable energy production method that decomposes water molecules into oxygen (O2) and hydrogen (H2) gases by employing electricity. Released H2 is utilized as an energy carrier whereas O2 is used in the energy conversion systems such as fuel cells. Water electrolysis systems are composed of an anode electrode where an oxygen evolution reaction (OER) occurs and a cathode electrode that is responsible for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). OER is often regarded as the main bottleneck of water electrolysis because of its sluggish kinetics which limits cell efficiency. The thermodynamic potential of the water electrolysis reaction is 1.23 V but there is a need for higher potential due to the various activation barriers. Thus, there has been extensive research for novel electrocatalysts. Noble metal-based oxides have been offered as promising candidates towards OER thanks to their superior activity. However, because of their poor stability and high cost, first-row transition metals such as nickel (Ni), iron (Fe), cobalt (Co), and manganese (Mn) have drawn a lot of attention for the OER in alkaline media. Ni showed superior properties among the others thanks to its corrosion resistance and ductility towards OER. Further research studies have revealed that the combination of Ni with Fe has increased the OER activity. Carbon-based electrocatalysts for OER have been found promising thanks to their good conductivity and high stability both in acidic and alkaline electrolytes. Later, it has been found that carbon materials with metal or nitrogen (N) doping have a higher surface area and the number of active sites as a result of the increasing dispersion. Consequently, uphill energy states of the catalytic intermediates have been decreased by the structural defects as a result of N doping. Accordingly, polyacrylonitrile (PAN) has been offered as advantageous carbon support due to N atoms in the structure. PAN-derived carbon-supported electrocatalysts have been synthesized via the electrospinning method in the literature up to date, which is an expensive method, and it is hard to optimize. Recently, a new synthesis approach which is "in-situ synthesis" has been proposed by our research group as an easier and inexpensive method. In the first part of this thesis, single metal-based (Ni) PAN-derived carbon-supported electrocatalysts were synthesized with the in-situ method which is a cheap and easy process. Then, the structures of these materials were characterized and investigated for OER activity with the electrochemical characterization methods. In addition, the chelating effect was examined using different chelating agents such as 2-2'-bipyridine and ethylenediamine, to observe the formation of the smaller nanoparticles. In the second part of the thesis, bimetallic systems (i.e. alloys) were synthesized in different ratios of Ni and Fe with the in-situ method. Structural and electrochemical characterizations were conducted to examine the relationship between Fe and Ni and their effect on the OER activity. In addition, the chelating effect was examined with the best resulting chelating agent. Consequently, 40% Fe1:Ni1@NC-bipy was exhibited the smallest overpotential, smallest Tafel slope, highest surface area, good crystallinity, and homogeneous dispersion of the nanoparticles.
Photocatalytic hydrogen production using layered perovskite oxides
Fossil fuels have a known impact on environmental pollution, and there is a possible scarcity of these fuels in the future. Because of this reason, cleaner and more abundant fuels may be preferred for substitution. Hydrogen, an eco-friendly and promising fuel obtained from electrolysis, is a strong candidate for this purpose. Since solar energy is renewable, electrolyzing water using semiconductors is a sustainable approach. The photocatalytic water splitting reaction can be done by using perovskite oxides, and there are many examples of perovskite oxide materials that can be found in the literature for this purpose. Among these perovskite oxides, layered perovskite oxides stand out because of their chemical stability, tunable morphology, and low-cost precursor chemicals. Sr2TiO4 and KCa2NaNb4O13 are layered perovskite oxides, which have a limited number of studies in the literature, were inspected for their hydrogen evolution capability in this dissertation. The stated molecular structures were studied both with and without dopants to determine their hydrogen evolution rates. Adding additives to a photocatalyst is a widely used method for bandgap engineering. In the study, the effect of copper and nitrogen addition was tested for Sr2TiO4 without the addition of a cocatalyst. Noble metals (Pt, Pd, Ru, Rh) were added to KCa2NaNb4O13 during the synthesis instead of being added later, and hydrogen production rates were evaluated. In addition, proton exchange method was used to increase the surface area of KCa2NaNb4O13 and change its electronic structure. The structural analysis methods, optical measurements, and hydrogen evolution tests were performed on these materials to evaluate their properties. According to the results, both materials were successfully synthesized, their bandgap changes were determined, and their hydrogen production rates increased after the doping and proton exchange processes.
Plasmonic nanoparticle modified substrate for SERS sensing applications
Numerous research on the toxicity of N-derived species like nitrite and ammonia have been conducted as a result of their widespread existence in the environment. The ecological system is threatened by nutrient pollution, which is mostly caused by heavy use of fertilizers. Another source of pollution is the industrial gas chimneys and internal combustion engines. Numerous analytical techniques, such as chromatography ,electrochemistry and colorimetry have been developed for the study of nitrite ions in the literature. Another advantage of developing NOx and NH3 detection devices is that they play a role in disease identification. Nitrite and ammonia are biomarkers used to diagnose lung and respiratory disorders, as well as kidney and digestive system diseases. Surface-Enhanced Raman scattering (SERS), due to its high sensitivity and resolution, has been extensively researched since its discovery on a rough Ag surface. Up to now, anisotropic noble metal nanostructures (Ag and Au) with tunable absorption bands in a wide spectral range have demonstrated high SERS activity via electromagnetic enhancement mechanism (EM). This dissertation is concerned with the manufacture of plasmonic metal particle substrates and their application to the detection of N-derived molecules. The first two parts present the synthesis of nanoparticles on copper plates. Ag and Au nanoparticle modified copper films with different morphologies are investigated. The homogeneous distribution of Ag and Au nanoparticles on the Cu surface resulted from successful assembly of nanoparticles and surface characteristics of the used copper plate. The final section presents the production of nanoparticles on a 3-D graphene oxide framework. Three-dimensional (3D) graphene materials with distinct characteristics have not yet been substantially investigated for SERS applications. Graphene aerogels (GA) with Ag modifications were used as SERS substrates in this research. SERS performance of substrates were examined by detecting an N-derived probe molecule; Rhodamine B (RhB). The highest-sensitivity substrate is then used for nitrite detection. The detection limit for RhB molecules is 10-8 M for Ag NPs modified Cu substrate, 10-16 M for Au-Ag NPs modified substrate, and 10-6 for Ag NPs modified GA substrate. The SERRS technique (Surface Enhanced Resonance Raman Spectroscopy) was used to study nitrite detection adopting azo dye production. The most promising substrate could achieve detecting nitrite concentrations as low as 10-14M.
Tailored doping strategies for photocatalytic CO2 reduction and water splitting on KCa2Nb3O10 layered perovskite
Global warming is defined as the long-term heating of the Earth's surface that has been observed since the pre-industrial period. This phenomenon is primarily driven by human activities, especially the use of fossil fuels, and is accompanied by various consequences such as the increasing global population and industrialization, leading to elevated greenhouse gas levels in the atmosphere and a reduction in green areas. The negative effects of global warming and related climate change, the world's most critical problem, are becoming more serious day by the day. Researchers and industries are pursuing two main approaches to address the challenge of reducing CO2 emissions. The primary approach is to tackle CO2 emissions at the production level by reducing reliance on fossil fuels and exploring alternative energy sources such as hydrogen energy. The second way is clearly to convert CO2 into useful products. Recently, photocatalytic reactions have gained popularity in converting CO2 to useful chemicals and producing H2 from water due to their features such as being environmentally friendly, simpler to set-up, more cost-effective, and more scalable. Yet, there is more to investigate about photocatalyst systems. The use of hole-scavengers to improve photocatalytic activity has been widely used, but the behavior of hole-scavengers on 2D nanosheets of perovskite photocatalysts has yet to be discovered. Another way to improve the photocatalytic activity is the utilization of co-catalyst particles on the surface of the photocatalyst. Given that only the surface atoms of particles actively participate in photocatalytic reactions while the inner atoms remain inactive, the sustainability of using co-catalyst particles, especially those incorporating noble metals, becomes a concern. Thus, it is crucial to disperse single-atom co-catalysts in a photocatalytic system. Hole scavenger study as a first chapter, aims to mechanistically investigate the photocatalytic performance of hole scavengers on nanosheets of 2D layered KCa2Nb3O10 perovskite oxide. A range of hole scavengers were added to the photocatalytic system to observe how they influence the charge carrier dynamics and overall photocatalytic efficiency. To analyze the behavior of hole scavengers on a [Ca2Nb3O10]- perovskite nanosheet, photoelectrochemical and photocatalytic experiments were utilized. Investigation of single site noble atom doped 2D layered perovskite for photocatalytic hydrogen evolution reactions is a second chapter. Pd noble metal was chosen for single-site atom doping. The incorporation of Pd as a single-site atom dopant altered the electrical band structure of the photocatalyst. Depending on the doping concentration, this caused the narrowing or shifting of the bandgap to visible spectrum. Also, it can serve as an active site for photocatalytic reactions, facilitating the transfer of charge carriers. Pd doping reduced the recombination rate of electron-hole pairs by providing additional reaction pathways, leading to more efficient charge utilization. In the last chapter, the photocatalytic CO2 reduction performances and photocatalytic activities were investigated by using ultrathin 2D layered Dion-Jacobson type perovskite oxide KCa2Nb3O10 with single-site ruthenium doping. To investigate the impact of ruthenium doping, a study on CO2 reduction was carried out using photoelectrochemical and photocatalytic methods. The nanosheets exhibited higher photocatalytic CO2 reduction activity. The main products obtained were methanol and ethanol. The findings presented in this study will shed light on the tremendous potential of ultrathin 2D layered Dion-Jacobson type perovskite oxide KCa2Nb3O10 with single-site ruthenium doping as a promising photocatalyst for CO2 reduction. This thesis holds significant implications for developing sustainable strategies to combat CO2 emissions and foster a greener future.
Investigation of phthalocyanine based 2D covalent microporous polymer (CMP) and 2D layered perovskite hybrid structure for photocatalytic water splitting reaction
January,15,2024 Today, global warming, caused by the rise in greenhouse gases due to industrialization and population growth, is leading to a severe increase in average temperatures on Earth's surface. These greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrogen oxides (NOx) and chlorofluorocarbons (CFCs). These gases, which accumulate in the atmosphere and cause the sun's rays to remain on the surface longer, contribute to the increase in temperatures. Industrial activities and increasing energy needs have increased the use of fossil fuels, seriously increasing air pollution problems and global warming. This situation disrupts the environmental balance, causing several adverse effects, such as climate change and extreme weather events. Therefore, controlling greenhouse gas emissions and shifting towards sustainable energy sources is critical in solving these global problems. Hydrogen energy stands out as an essential approach to clean energy production. However, despite research in this field, this problem still needs to be solved effectively enough. Covalent microporous polymers (CMP) appear in different designs in the literature, are microscopically porous, and consist of building blocks connected by covalent bonds. Large surface areas and a structure with high p-conjugation are essential features of these polymers. With their wide range of building blocks and different synthesis techniques, they can be customized in many different areas of the industry, such as gas storage and adsorption, sensor technology, biological applications, heterogeneous catalysts, and photocatalytic water splitting. This research addresses the search for a solution to an efficient photocatalytic water-splitting reaction to contribute to the hydrogen economy with green hydrogen production. CMPs are used to solve the problem. CMPs in this study are composed of Phthalocyanine and [2,2'-bipyridine]-5,5'-dicarbaldehyde building blocks, which increases the π conjugation of the polymer. This covalent microporous structure containing imine bonds has been described for the first time in the literature. In this study, the effect of metal on photocatalytic water splitting studies was examined within the scope of zinc and nickel metals bonded on phthalocyanines. This study introduced a covalent micropore polymer photocatalyst with a stable structure to the literature. We have presented a CMP structure with different metal centers as a photocatalyst capable of producing hydrogen gas from water under illumination.
Development and characterisation of high-entropy alloys (HEAs)
This doctoral thesis presents a comprehensive investigation into the potential applications of High Entropy Alloys (HEAs) as protective coatings for biomedical implants and as electrocatalysts for water-splitting applications. The research spans five main chapters, each exploring different facets of HEAs, including their microstructure, mechanical properties, electrochemical behavior, biocompatibility, and catalytic performance. Chapter three highlights the deposition of Ti1.5ZrTa0.5Nb0.5Hf0.5 RHEA films on 316L, CoCrMo, and Ti6Al4V substrates, revealing amorphous, compact structures with superior mechanical properties and adhesion, particularly on the Ti6Al4V substrate, and demonstrating enhanced corrosion resistance in PBS solution. Chapter four focuses on different RHEA films on 316L substrates, identifying potential as protective coatings due to improved hardness, tribological performance, and biocorrosion resistance, with biocompatibility confirmed through in vitro tests. Chapter five discusses both undoped and Ag-doped Ti1.5ZrTa0.5Nb0.5W0.5 RHEA films, noting the mechanical and corrosion-resistant benefits of Ag nanoparticle inclusion. Chapter six details the development of antibacterial RHEA films doped with Ag nanoparticles, showing significant antibacterial efficacy against P. Aeruginosa and S. Aureus, and promising biocompatibility with C2C12 myoblast cells. Collectively, these studies underscore the potential of RHEA films as functional coatings for biomedical applications. The seventh chapter explores the preparation of CoCuFeNi-based HEAs through mechanical alloying (MA) and their evaluation as electrocatalysts for water splitting. The results show that CoCuFeNiMnMo1.5 exhibits the best OER performance, while CoCuFeNiMnMo0.5 demonstrates the best HER activity with lower overpotentials and excellent stability. The assembled CoCuFeNiMnMo1.5 (anode)∥CoCuFeNiMnMo0.5 (cathode) couple achieves a current density of 10 mA cm–2 at 1.76 V, with a Faradaic efficiency for generated H2 of more than 80%. In conclusion, this thesis provides valuable insights into the potential of HEAs as protective coatings for metallic biomaterials and as efficient electrocatalysts for water splitting, contributing to the advancement of HEA research and the development of novel materials with enhanced properties for biomedical and energy-related applications.
Doping strategy for enhanced photocatalytic hydrogen production on tantalum layered perovskite nanosheets
Rise in greenhouse gas levels due to human activity, such as burning fossil fuels, causes global warming and environmental problems. Thus, industries and researchers are investigating alternative energy sources to find solutions to environmental problems and slow down global warming. Hydrogen is one of the solutions to these problems. Semiconductor photocatalysis has been researched for hydrogen production as a sustainable energy source since the 18th century. Many photocatalysis materials, such as metal oxide, metal sulfide, and metal nitride, have been studied and used as photocatalysts. In addition to these materials, layered perovskite oxides have gained significant interest in the photocatalytic field over the last 20 years—the heightened interest results from its tunable band structure, flexible interlayer structure, and tunable morphology. Furthermore, exfoliating layered materials gives 2D building blocks of bulk materials. Resulting nanosheets with few atomic layers offer a high surface area, low migration distance, and high charge separation to improve photocatalytic activity. Although there is a vast interest for efficient H2 production with photocatalytic water splitting, research on H2 production activities needs a long way to go to achieve solar hydrogen efficiencies above 10%, raising questions about strategies to achieve effective photocatalytic activity. The common approach to achieve a high productivity from a photocatalyst is to use co-catalysts, which improves charge separation in photocatalysts. In general, noble metals like Pt are used as cocatalysts in nanoparticle form on the surface of photocatalyst. In this case, the inner atoms of the catalysts are inactive since only surface atoms play a role in catalytic activity. In this study, the effects of introducing Pd, Sn, and N into the structure were conducted for photocatalytic hydrogen production in an aqueous 10 vol.% methanol solution as a sacrificial agent without cocatalyst. After exfoliation of tantalum based perovskite oxide, PdO6 and SnO6 octahedra were formed when Ta was substituted iv with Pd or Sn, which acted as a single-atom catalyst site (SACs). These obtained octahedra structures reduce the original phase's electrical structure and serve as sites for trapping electrons, thereby reducing the recombination rate of photo-induced carriers. Furthermore, exfoliated materials have high surface areas, making them ideal platforms to disperse SACs uniformly. This allows for the use of all metal atoms added to the structure with nearly 100% photocatalytic activity. On the other hand, nitrogen, which is partly substituted for oxygen, has a great potential to minimize electronic band energies due to the formation of isolated electronic states positioned above the top of the oxygen (O) 2p valence band. Various structural, spectroscopic, and electrochemical characterization techniques were used to analyze materials' properties in detail. According to the results, all target materials were successfully synthesized, their bandgap changes were determined, and their hydrogen production rates increased after the doping and proton exchange processes
Grafen (oksit) - metal/metal (hidr)oksit kompozitleri: sentezi ve elektrokimyasal enerji depolama ve dönüşümü için uygulamaları
The massive energy demand in the world will be supplied by renewable energy sources (solar, wind, etc.) with the inevitable depletion of fossil fuels. However, efficient utilization of these sources heavily depends on the development of advanced energy storage and conversion devices due to their intermittent nature. In this regard, electrochemical capacitors, batteries, and fuel cells are the main electrochemical systems that can assist the continuous operation of the renewable sources, or offset the daily energy need individually. The common component in all the electrochemical energy devices is the electrodes which contain active material and the current collector. Physicochemical properties of the active material determine the overall device performance. This dissertation is devoted to the synthesis of graphene oxide (GO) - metal/metal (hydr)oxide composite electrodes for electrochemical applications. In the first part, production of two-dimensional composite electrodes is presented as electrochemical capacitor electrodes. First row transition metal cations (Co2+, Ni2+, Mn2+, Fe2+) and GO were combined by utilization of simple electrostatic interactions. The highest capacitance was obtained with Fe/GO (38.7 mF cm-2) followed by rCo/GO (31.6 mF cm-2) and rFe/GO (29.1 mF cm-2) at 20 mV s-1, where r represents electrochemically-reduced composites. The nature of the metal was influential in the charge-storage mechanism of the composites: while rCo/GO and rNi/GO were governed by diffusion-limited processes, rMn/GO and rFe/GO showed pseudocapacitive behavior. Furthermore, ultrathin electrodes of Ni(OH)2 and GO were produced via layer-by-layer assembly (LBL) followed by hydrazine vapor reduction to enhance electrical conductivity of GO. Reduced 9-bilayer [Ni(OH)2/GO] film exhibited areal capacitance of 8.6 mF cm-2 at 2 mV s-1, 3-fold higher than that of LBL-assembled [CoAl LDH/rGO] thin film reported in the literature. LBL-assembly was also utilized to produce superparamagnetic iron oxide nanoparticles (SPION)/GO thin films. State-of-the-art electron paramagnetic resonance results revealed the competition between carbon defect centers and Fe-related paramagnetic centers on the electrochemical performance. In fact, reduced 1-bilayer [SPION/GO] had enhanced specific capacitance of 1570 F g-1 at 5 mV s-1, outperforming all the LBL-assembled iron oxide/rGO films and most of the transition metal oxide/rGO composites in the literature. In all the LBL-grown composites, as-deposited films exhibited pseudocapacitive properties, whereas hydrazine-reduced films showed more diffusion-limited charge storage, like in batteries. In the second part of the thesis, synthesis of graphene aerogels (GAs) is presented as the next-generation three-dimensional form of graphene. One-step hydrothermal treatment of GO solutions resulted in formation of high surface area GAs (~700 m2 g-1) with the aid of supercritical CO2 (scCO2) drying. Obtained metal-free GA electrodes on nickel foam exhibited superior specific capacitance (390 F g-1 at 5 mV s-1) than the counterparts reported in the literature. GAs were later decorated with metal nanoparticles as possible electrocatalysts for oxygen evolution (OER) and oxygen reduction reactions (ORR). Ni/GA composites were synthesized via one-pot hydrothermal reaction coupled with thermal reduction under H2/He environment as possible OER electrocatalysts. By using urea as the continuous hydroxyl ion supplier during the hydrothermal reaction, Ni loading was tuned between 1.5 and 40 wt % in a highly-controlled fashion. Ni/GA with 40 wt % Ni exhibited low overpotential of 320 mV for the supply of 10 mA cm-2 which is 110 mV lower than that of 80 wt % Ni/GA and 50 mV lower than that of 20 wt % Ir/C and 20 wt% Ru/C reported in the literature. Lastly, Pt loaded GAs were synthesized by scCO2 assisted deposition as possible ORR electrocatalysts. Pt nanoparticle size was varied from 1.2 to 2.9 nm by increasing the thermal conversion temperature from 400 to 800 °C. Simultaneously, gradual thermal deoxygenation of GA was observed. Obtained Pt/GA converted at 600 °C had enhanced electrochemical surface area of 102 m2 g-1, which is higher than that of commercial Pt/C. Overall, the mass activities of Pt/GA electrocatalysts followed the order: Pt/GA(600)>Pt/GA(400)>Pt/GA(800).
Perovskit oksitlere dayalı CO2 gaz sensörlerinin araştırılması ve geliştirilmesi
The need for energy rapidly increased with the development of humanity and technology. The required energy has been mainly provided by fossil fuels such as coal, natural gas, and oil. However, these sources are limited and nonrenewable. Additionally, massive consumption of these sources is causing environmental problems like global warming via the greenhouse effect. Increased CO2 ratio in the atmosphere is causing solar energy adsorption and keep the heat close to the Earth's surface. Furthermore, CO2 is used for many purposes in daily life such as in refrigerators, fire extinguishers, carbonated drinks, or manufacturing processes. Thus, CO2 has a crucial role on the carbon cycle which is necessary for the living creatures and the Earth, but it harms human health when it is not properly handled. It is highly important to control the level of CO2 in the environment for comfort and health. Thus, main purpose of this study is to develop chemiresistive CO2 sensing materials and manufacture highly efficient and low-cost sensor and also another the synthesis and characterization of ABO3 type perovskites and examine them as CO2 sensing materials. In the presented work, LaMnO3 and LaTiO3 based undoped and doped perovskites were prepared with sol-gel method and the films of these perovskites were examined for CO2 sensing. The film were deposited with electrophoretic deposition and spin coating methods. Material characterization was performed with various techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM). Porous structure and surface area of the powders were the most important parameters for a good sensing material. Thus, the dopant ratio and dopant type were examined carefully with homemade sensing setup to obtain the best working sensing material. Also, gas sensing properties were studied different parameters like temperature, and gas concentration to obtain optimum conditions.