LEE- Nano Bilim ve Nano Mühendislik Lisansüstü Programı

Bu topluluk için Kalıcı Uri

http://hdl.handle.net/11527/19415

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3D printed antibacterial herbal loaded alginate-pectin medical patch: Fabrication and characterization

(Graduate School, 2022-07-07) Dini, Ghazaleh ; Benli, Birgül ; 513201032 ; Nanoscience and Nanoengineering

This thesis focuses on a comprehensive and multi-disciplinary approach to the development of an effective and sustainable wound dressing. The thesis consists of three main parts, each layer building upon the previous to create a final product that is both innovative and practical. In the first part, the necessary materials such as pectin was synthesized in order to serve as the base layer of the wound dressing. This involves careful selection and testing of materials to ensure that it meets the necessary requirements for strength, flexibility, and biocompatibility. In the second part of the thesis, the antibacterial agents from herbal extracts were prepared. These natural agents offer several advantages over synthetic alternatives, including reduced toxicity and improved biocompatibility. Also, natural and biocompatible nanoclay as a carrier for these agents were used to controlled release, with the assistance of synthesized cellulose which was extracted from waste fruits, expected effects were improved, and targeted delivery to the wound area. In the third and final part of the thesis, advanced 3D printing technology was used in two ways. Firstly, a skeleton was designed for the prepared hydrogels using 3D printing. This skeleton provides structure and support for the hydrogel while allowing for air flow and moisture control. Secondly, the polymers (pectin:alginate/gelatin and nanoclay loaded ones themselves were 3D printed using Fused Deposition Modeling (FDM). We also integrated the hydrogel and clay material to form more hydrophilic film patch that is both strong and flexible. The final product is an antibacterial wound dressing that combines advanced materials and technologies to promote healing and prevent infection. This innovative approach has the potential to revolutionize wound care and improve patient outcomes. As it has been demonstrated in literature, wound healing is a complex and intricate process that involves multiple stages and requires the right type of dressings to prevent infection and promote the regrowth of tissue. The ideal dressing should have several key properties, including the ability to keep the wound moist, allow air to flow through, protect the wound from external contaminants, absorb excess fluid, and be easy to remove without causing additional damage to the wound. Hydrogels are an excellent choice for wound dressings due to their unique physical and chemical properties. These materials are highly absorbent and can retain large amounts of water, which helps to keep the wound moist and promote healing. A hydrophilic wound dressing is necessary for rapid therapeutic effect and absorption of exudate. This characteristic also helps to maintain a moist environment, promote high blood absorption, and enhance erosion capability and it was measured with contact angles. They are also permeable to gases, allowing air to flow through and providing xx oxygen to the wound. Additionally, hydrogels can be formulated to have antimicrobial properties, which can help to fight against bacteria and prevent infection. In this thesis, pectin was synthesized from pomegranate and grapefruit peels using citric acid extraction and cellulose was synthesized from pomegranate peels, making the study sustainable and environmentally friendly. Also, the fallen fruits from the grapefruit trees in the faculty garden were collected and utilized in the study, emphasizing their significant contribution to the fruit industry and agricultural research. Additionally, the effect of grapefruit juice instead of citric acid was alternatively used during the process of pectin extraction with the aim of achieving zero waste. Malva sylvestris and Cichorium intybus L, two local Turkish herbs, were used as antibacterial agents. The extraction of these herbs was done using microwave-assisted extraction with ethanol and membrane-assisted purification methods. Additionally, dialysis tubes which are kind of membrane, were used during the purification of antibacterial herbal extracts and the resulted extracts were compared with traditional extraction methods. The synthesized extracts were analyzed using optical spectroscopy techniques such as UV-Vis Absorption Spectroscopy. Herbal extracts were loaded into Halloysite nanotubes (HNTs) and injected into the hydrogel pores in order to help with air flow in the hydrogel area. Glycerol also used as a plasticizer. The process of extracting materials from plants and fruit wastes was also carried out using microwave-assisted synthesis methods, which are low-cost and time-efficient. The effectiveness of Malva sylvestris and Cichorium intybus L against bacteria was examined using the disc diffusion method. Their antibacterial activities were tested against E. coli and S. aurous that are effective two common types of wound bacteria to create pectin/alginate-based hydrogel wound dressings. Disc diffusion tests confirmed the antibacterial activity of the chosen plant extracts against common wound bacteria. To improve the effect of nanotubes such as high water absorbency and elongation as fillers of reinforced hydrogels composites, cellulose was synthesized. Ash content tests and moisture level measurements of the synthesized pectin and cellulose confirmed their high purity. In the next stage of the thesis, biopolymers and HNTs were combined to form a composite that was used to formulate a hydrogel that could be used inside a 3D printed skeleton. To design an effective antibacterial patch, 3D FDM printer were used. A patch-shaped skeleton with several pins were designed using 3D printing technology to make the hydrogel porous masks. The pectin/alginate based composites were poured on top of a cross-linker solution to form the hydrogel on the mask surface. Then, the pectin/alginate based hydrogels were cross-linked with calcium chloride (CaCl2). In the final stage of the thesis, formulated layer from cellulose and HNTs composite were prepared. These nanoclays were designed to act as carriers for herbal extracts. The effectiveness of these hydrogels in preventing bacterial growth was also tested against common wound bacteria, E coli and S. aurous and the results were successful. Additionally, the ability of these hydrogels to absorb water was evaluated using a gelatin hydration test. The behavior of the hydrogels was also examined in detail. In conclusion, the results showed that hydrogels containing either Malva sylvestris or Cichorium intybus L plant extract have great potential as antibacterial patches for xxi wound dressing. However, further in vivo studies are necessary before any clinical application can be made.
Comparison of naproxen-loaded zeolitic imidazolate frameworks (ZIF) and halloysite nanotube-zif composites with 3D printed PLA embedded in gelatin hydrogel

(Graduate School, 2024-07-17) Çetin, Reyhan ; Benli, Birgül ; Özatay Gök, Özgül ; 513201034 ; Nanoscience and Nanoengineering

Nanomedicine is an interdisciplinary discipline that integrates nanotechnology with biomedical sciences. It brings about a revolution in illness management by introducing revolutionary methods in diagnosis, treatment, and prevention. A crucial element of this development is the investigation of nanocarriers, vital constituents in sophisticated pharmaceutical delivery systems that aim to surpass biological obstacles and facilitate precise and regulated drug discharge. Within this framework, the study specifically examines two types of inorganic nanocarriers, namely Zeolitic Imidazolate Frameworks (ZIFs) and Halloysite Nanotubes (HNTs). These two nanocarriers possess similar distinctive characteristics, which make them well-suited for a comparative analysis. ZIFs, which are categorized as metal-organic frameworks (MOFs), possess a wide range of beneficial characteristics that are essential for their function as nanocarriers in nanomedicine and drug delivery systems. The characteristics of these materials encompass high porosity, modifiable size and structure, convenient surface alteration, minimal toxicity, significant loading capacity, improved stability, favorable biocompatibility, water solubility, and biodegradability. ZIFs exhibit pH-responsive properties, allowing for the targeted release of medications in response to changes in acidity. This attribute improves the accuracy and timeliness of drug administration. In comparison, Halloysite Nanotubes (HNTs) belong to a different category of inorganic nanocarriers that offer exceptional characteristics, making them extremely desirable for use in medicinal applications. The inherent tubular morphology of HNTs enhances their biocompatibility, extensive surface area, and capacity for surface modification, making them highly favorable for applications as drug delivery systems. HNTs possess the ability to release drugs in a controlled and prolonged manner, while also having less toxic effect and being naturally abundant. This makes them highly adaptable and beneficial in the field of pharmaceutical sciences. Furthermore, HNTs possess antibacterial properties, which are essential in situations when it is necessary to prevent the growth of germs. The pH-responsive drug release properties of HNTs further facilitate accurate and focused medication delivery. Therefore, HNT- ZIF combination was designed and synthesized to analyze how the properties of HNT effect the properties of ZIF, comparing with synthesized ZIF. Hydrogels that are known for their capacity to absorb water and compatibility with living organisms and are crucial in the field of biomedicine, particularly in applications such as wound dressings and drug delivery systems. The scaffold structures used in tissue engineering, particularly when paired with poly(lactic acid) (PLA), play a significant role in promoting cell proliferation and tissue regeneration. PLA offers advantages such as providing structural reinforcement and undergoing a progressive process of biodegradation. The combination of hydrogel and PLA scaffold, facilitated by 3D printing technology, improves accuracy and personalization. The benefits of utilizing 3D printing in tissue engineering encompass the capacity for replication, expandability, and the capability to fabricate structures with regulated porosity. The combination of these elements has the potential to generate groundbreaking solutions in the field of regenerative medicine. The aim of the study was to combine two distinct patches: one comprising a composite gelatin hydrogel and PLA scaffold with Naproxen, a nonsteroidal anti-inflammatory drug, loaded ZIF embedded within it, and the other comprising a composite gelatin hydrogel and PLA scaffold with Naproxen loaded HNT-ZIF embedded within it. The objective is to evaluate and compare the drug loading capacity, drug release behavior and pH responsiveness To determine their properties using various techniques, including scanning electron microscopy (SEM), Liquid Chromatography–Mass Spectrometry (LC-MS), Energy-Dispersive X-Ray Spectroscopy (EDS), swelling capacity determination, drug release analysis, pH responsiveness analysis, and in vitro cytotoxicity study. They were successfully completed. Based on examinations, ZIF and HNT-ZIF composite were synthesized successfully and their bonds and each size of synthesized nanoparticles were quite similar with literatures, which FT-IR graphs and SEM images proved. Data of EDS and FT-IR demonstrates that Naproxen was loaded into synthesized nanocarriers and according to LC-MS results show approximately %92 efficiency. Drug release and pH responsiveness analysis demonstrates HNT-ZIF had lower release rate and both HNT-ZIF and ZIF were pH responsive. Additionally, SEM images show that gelatin hydrogel has too small pores and polymer layers. Moreover, swelling capacity of PLA embedded gelatin hydrogel was quite stable due to strong mechanical properties of PLA. The results of toxicity shows that HNT may contribute to increased cell viability in HNT-ZIF due to block the release of ions from organic linkers of ZIF. In high concentration of ZIF, cell viability was higher than followed decreased concentration with 1:2 dilution due to the fact that it was agglomerated. In lower concentration, especially 0.0025 mg/µL, there could be more released ZIF without agglomeration. Moreover, the incorporation of hydrogel nanocarrier composites significantly enhances cell viability compared to samples lacking hydrogels. This demonstrates that hydrogel effectively slows down the release of ions and drugs.
Composite carbon nanofiber anodes for na ion batteries

(Graduate School, 2022-06-02) Abdolrazzaghian, Elham ; Yanılmaz, Meltem ; 513201009 ; Nanoscience and Nanoengineering

Nanofibers are one of the most important nanomaterials and have many applications in diverse fields such as biomedical engineering, drug delivery, filtration, sensors, energy storage etc. due to their unique properties like high specific surface area, small diameters, uniform interconnected 3D porous structure and low weight. There are different types of techniques to produce nanofibers like self-assembly, drawing, melt-blowing, phase separation, electrospinning and centrifugal spinning. Due to special features of centrifugal spinning such as high production yield and safe production, it is one of the most promising methods to prepare nanofibers. In this technique, nanofibers are made by applying centrifugal force on polymer solution or melt by using a high-speed rotating spinneret which lead to form nanofibers on collectors. In centrifugal spinning method, the morphology of nanofibers is dependent on diverse processing parameters such as viscosity, surface tension, molecular structure, molecular weight, solution concentration, solvent structure, additive; and operational conditions such as rotational speed, feeding rate, nozzle diameter, and nozzle-collector distance. Energy and environment head the list of top global problems facing society in the twenty-first century. Nanotechnology is responding to these challenges by designing and fabricating functional nanofibers optimized for energy and environmental applications. Nanofiber materials have been extensively studied as constituent parts of energy conversion and storage devices. Lithium ion batteries (LIBs) are rechargeable batteries and have been widely used in different applications like portable electronic devices and electric vehicles due to their high energy density, however limited lithium sources lead to find another option. Production of sodium ion batteries (SIBs) are gaining great attention due to low-cost and high abundance of sodium resources. Rechargeable batteries consist of an anode, a cathode, an electrolyte and a separator. Conventional materials used as anode suffer from large volume expansion, leakage, pulverization and low conductivity whereas carbon nanofibers have been widely used in electrochemical energy storage devices because of their excellent conductivity, extremely large surface area, high porosity, mechanical flexibility and structural stability that will improve capacity and cycling performance when they are used as electrodes in sodium-ion batteries. The performance of these materials is greatly influenced by the material type; structure; mechanical, chemical, thermal stability and physical properties. For example, if the surface area and porosity increased, the permeation of the electrolyte increases, so the electrode can provide higher sodium storage capability and the electrode will have shorter transport length for sodium ions. Heteroatom doping is one of the best ways to increase the surface area and porosity of nanofibers so enhanced sodium ion insertion and desertion at high rates can be achieved. Until now, composite carbon nanofiber using various materials such as tin, iron, antimony and molybdenum have been widely investigated as the anode materials in SIBs, since they possess high theoretical capacity, environmental benignity, safety, and low cost. In the first part of the study; it was aimed to fabricate carbon nanofibers as anodes for sodium ion batteries via centrifugal spinning. PAN was used as carbon fiber precursor because of its high carbon yield, high thermal, chemical and mechanical properties. Also, PS was blended with PAN in order to increase the porosity of carbon nanofibers. Moreover, graphene with a two-dimensional honeycomb structure was used to improve the electrochemical performance of the LIBs and SIBs, due to its high theoretical specific capacity, large specific surface area, and good electronic conductivity. In addition, the effect of Molybdenum disulfide (MoS2) on performance and electrochemical capacity of LIBs and SIBs was investigated. PAN/PS/graphene polymer blend solution was prepared in DMF and centrifugally spun in order to obtain nanofibers. Nanofibers were fabricated at the rotational speed of 4000 rpm, feeding rate of 60 ml/h, with 0.5 mm nozzle diameter and 20 cm collector distance. After obtaining nanofibers, blend nanofibers were stabilized in air atmosphere at 280 ℃ for 2.5 h with a heating rate of 5 ℃/min and then carbonized in nitrogen atmosphere at 800 ℃ for 2 h with a heating rate of 2 ℃/min. Furthermore, MoS2 decorated graphene-containing porous carbon nanofibers were fabricated via hydrothermal synthesis. The morphology and average fiber diameter distribution were analyzed with SEM. Porous structure of the carbon nanofibers was observed via TEM images. XRD and Raman spectroscopy were used for structural characterization. Porous structure enhanced the electrochemical performance of electrodes. Furthermore, MoS2 decorated graphene included porous CNF improved the electrochemical capacity up to 860 mAh/g in Li-ion cells and 455 mAh/g in Na-ion cells with excellent cycling performance. In the second part of the study; it was aimed to fabricate carbon nanofibers by using water soluble polymers such as PVA and PVP. Considering environmental concerns, it is vital to fabricate carbon nanofibers from environmentally friendly materials. PVA/PVP nanofibers were fabricated via fast and safe centrifugal spinning. The effect of PVP content on the morphology and thermal properties of PVA/PVP blend nanofibers were studied by using SEM and DSC studies. Moreover, the effect of carbonization conditions including stabilization time, stabilization temperature, carbonization time, carbonization temperature on morphology and carbon yield was investigated.
Comprehensıve analysıs of vıtamın D3 adsorptıon and monıtorıng usıng QCM wıth hydrophobıc algınate-halloysıte nanoclay composıte bılayers

(Graduate School, 2024-06-14) Kirazoğlu, Mervenur ; Benli, Birgül ; 513211010 ; Nanoscience and Nanoengineering

Biosensors that use quartz crystal microbalance (QCM) provide an alternative to analytical methods. They can track binding events in real-time and have very sensitive bulk detection capabilities. QCM analyzes the impact of deposits adhering to a quartz crystal on its vibration frequency. In addition to the economic and practical benefits, QCM sensing offers several inherent advantages in biosensors. First of all, the binding process may be observed and analyzed in real time because to the QCM's fast reaction. It enables researchers to quantify the binding kinetics, such as the association and dissociation rates, of the protein to the sensor surface. This information can be crucial for understanding the protein's behavior and for developing new drugs or diagnostic tools. Secondly, it eliminates the requirement for labeling to detect affinity events. This reduces complexity and allows for more streamlined detection processes. Thirdly, unlike other sensing techniques, QCM is not dependent on the optical properties of the surrounding media, making it versatile and applicable in a wider range of environments. One additional benefit is its capacity to identify variations in the viscosity and viscoelasticity of the solution and the biointerface, respectively. This capability provides valuable information about the molecular interactions and binding events taking place. Lastly, QCM sensing can be easily combined with other transduction techniques such as electrochemistry or spectrophotometry, enhancing its versatility and potentially improving detection sensitivity. QCM sensors have faced challenges in utilizing tiny molecules for coating due to limitations in fabrication devices. This has made it challenging to design QCM sensors suitable for continuous media. However, composite materials provide an alternative approach to modifying quartz crystal surfaces and broaden the applications of QCM sensors. Furthermore, the specificity of sensors utilizing nanoparticles and nanocomposites could be enhanced through the modification or creation of a novel sensor capable of accurately detecting the desired substance in real-world samples. In recent decades, there has been an increasing interest in delivery methods based on biopolymers due to their non-toxic nature, convenience, and wide range of application areas. One biopolymer of interest is alginate and its derivatives, which are widely accepted as important matrices for controlled release systems. Alginate is a naturally occurring polysaccharide consisting of α-l-guluronic acid and β-d-mannuronic acid monomers that are connected in different ratios. The food and pharmaceutical sectors frequently utilize sodium alginate, one of its sodium salts, as a gelling, thickening, and stabilizing ingredient. Alginate's primary property is its capacity to combine with divalent metal ions to generate insoluble crosslinked gels that resemble egg boxes. The properties of the resulting gel depend on the type of metal ion used for crosslinking, with magnesium ions being unable to form a crosslinked structure. Hydrophobic modification enhances the stability of sodium alginate in various environments, such as acidic or alkaline conditions, high temperatures, and organic solvents.
Computational design and analysis of nanostructured materials for neuromorphic engineering

(Graduate School, 2024-03-04) Turfanda, Aykut ; Ünlü, Hilmi ; 513192004 ; Nano Science and Nano Engineering

We study electronic structure of nanometer-scale materials using electronic structure theories like density functional theory. Nanoscale two-dimensional intelligent materials under strain, and their applications as electronic devices for neuromorphic computing is investigated. Combination of two-dimensional materials with other materials are in the scope of this work. Density functional theory calculations are done using Quantum ESPRESSO simulation suite. Designed and analysed neuromorphic electronic materials are simulated and compared with available technological data.Thesis has significance in terms of the choice of materials; secondly, in terms of the realization of homostructures, and heterostructures, and understanding the mechanical strain effects in these structures; thirdly, in terms of the application area; namely, neuromorphic electronic devices for memories. The overall purpose and the scope of the thesis can be listed chapter-wise. In Chapter 2, "Single atom precise, ultrafast, and universal emulation of biological synapses using atomically thin vertical heterostructures": We realize the current voltage-like characteristics of heterostructures using density functional theory and Boltzmann transport methods, which can reveal the hysteresis characteristics. Moreover, we used time dependent density functional theory to show characteristics of synapses. We show a healthy synapse with N vacancy and dysfunctional synapses with pristine heterostructure. We heal the dysfunctional synapses using N intercalation. Here, a single atom can manipulate the behavior of different synapses. Created heterostructures have different abilities of learning, memory, and so on. One can use these heterostructures to realize certain brain regions on chips because every region of the brain is responsible and superb in one ability mostly. In Chapter 3,"Mimicking bacterial learning and memory in tungsten based two-sided single layers of WSeO, WSeS, WSeSe, and WSeTe": The current literature about neuromorphic materials is based on showing how one can resemble to synapses and neurons of Human using two-dimensional materials. In this chapter, we are showing for the very first time to the best of our knowledge how to use 2D materials to mimic the characteristics of the bacterial learning and memory. We developed methods to show this in 2D materials using a quantum memristor and phase-change like mechanisms. Our modeling is directly comply with the gene regulatory network's governing equation of bacteria, also physical model resemble to the real world bacteria, which is supported by experimental biological letters. In Chapter 4,"Single-electron-precise tailoring of a resistive-switching device with transfer printing": We focus on how to replace the electrochemically active top electrode of a conductive filament forming resistive switching device with an inert electrode. For this, we study a molecular junction to design and model a resistive switching device based on a single-electron box effect, where the molecular junction composed of self-assembled monolayers. Resistive switching is establish through the penetrating Au atoms from the inert top electrode after transfer printing process. Here, Coulomb blockade effect through Au island and tunneling through the self-assembled monolayers are the two effective phenomenon to explain the resistive switching. To conclude, a molecular junction is studied using the methods of density functional theory and environmental effects are modeled using the Quantum ESPRESSO's module environ. In Chapter 5, "Computational Analysis of Device-to-Device Variability in Resistive Switching devices through Single-Layer Hexagonal Boron Nitride and Graphene Vertical Heterostructure Model": We show a simple model for defects and their effects at the interfaces of atomically thin heterostructures by varying the interlayer distance between two atomically thin materials forming the heterostructure. This model will allow us to gain insights into variations in current-voltage characteristics of resistive switching devices compose of metal-insulator-metal vertical structures using the methods of density functional theory. We believe this approach of modeling interfaces with varying distances and showing how it affects the current-voltage characteristics is first time interpreted in this way. Also, the last subsection reveals a very important and easy way to mimic the neurons. In Chapter 6,"Atomistic origins of compound semiconductor synthesis with computational neuromorphic engineering": This article can be considered a follow-up to our previously published article in the Journal of Applied Physics titled 'Mimicking Bacterial Learning and Memory in Tungsten-based Two-sided Single Layers of WSeO, WSeS, WSeSe, and WSeTe.' In this new chapter, we apply a similar methodology to another bacterium. However, the primary objective of our new article extends beyond this. Our aim is to demonstrate the potential for memristivity during compound semiconductor synthesis. It is widely recognized that the fabrication process using chemical vapor deposition based methods lacks a comprehensive understanding in terms of chemical kinetics. We endeavor to elucidate how growth processes exhibit learning behavior and possess memory. This is achieved through the analysis of the smallest potentially meaningful subunit of the growth: the resonant tunneling diode structure. Furthermore, we illustrate how the convergence of various computational methods—such as tight-binding, density functional theory, transfer matrix, and Boltzmann transport theory—can contribute to the design of future multinary memristors. Specifically, $sp^3s^*$ semiempirical tight-binding methods are predicting energy band gaps more accurately than density functional theory at a low computational cost and allow the investigation of compound semiconductors. Our work throughout this thesis is mainly based on density functional theory. Here, we will consider electron density to investigate the electronic structure of the materials. In this way, researchers found functionals, which are connecting the density with the energy. Density functional theory is based on interacting electrons in an external potential. The ground state energy is determined as the unique functional of the electronic density, which means that the ground state electron density is enough to construct the Hamiltonian of the system, and it verify that the construction of many electron wave function is not required to calculate the ground state properties. To conclude, we believe that the computational studies of nanoscale two-dimensional materials using the methods of applied computational materials science can enhance the performance of the neuromorphic devices.
Design and simulation of a microfluidic biochip for optic detection with derivatized microbeads and the biochemistry of learning

(Fen Bilimleri Enstitüsü, 2020) Tüysüz, Tuğçe ; Alptürk, Onur ; Uludağ, Yıldız ; 630291 ; Nano Bilim ve Nano Mühendislik

Microfluidic systems are an important technology suitable for a wide range of applications due to their rapid response capabilities, low cost and, small amounts of sample need. Microfluidics tries to overcome difficulties in conventional assays in medical diagnosis. The combination of biosensors and microfluidic chips increases the analytical capability to extend the scope of possible applications. In this thesis, two types of microfluidic modeling were designed for biomedical applications. The first design is a bead derivatized sensor in a microfluidic chip to detect biomarkers. The second model is designed to observe the effect of α-syn protein which constitutes the communication of two nerve cells through channels in the microfluidic system and the long term potentiation. In Project 1, Integrated affinity sensors within microfluidic platforms show great interest in life environmental and science analytical science applications. They are generally placed in the base of a fluidic flow channel on which an analyte solution is passed. The analyte detection on the sensor depends on the event of a recognition-binding, most generally antigen-antibody, for which the recognition molecules are attached to the surface of the sensor for the analyte. The analyte -recognition molecule complex is detected on the sensor. The integration of bead-based immunoaffinity assays in microfluidic chips has recently become an area of interest for many researchers. Integrated affinity sensors inside of the microfluidic structures have many advantages which are low-cost, rapid, highly specific detection and sensitivity. In this study, the microfluidic system has been designed with different substrate patterns in the continuous flow of phosphate-buffered saline (PBS), and microbeads were examined. Functionalized microbeads have been used as biomolecules to enhance the affinity of biomarkers and for high sensitivity. Microchannel was patterned with square pyramid well array, conic well array, triangle pyramid array, and the each microbeads made of polystyrene were placed into the each microwell; PS beads were simulated with different flow rates. Initially, PBS was utilized to simulate blood serum, and PS nanoparticles, functionalized and fluorescently labeled nanoparticles that allow detection of biomarkers, were simulated for examination by fluorescence microscopy. As a result of three different geometric well chip patterns and three different bead size simulations, it was determined that the shape of the well should be conical and the bead size should be 150 µm. The lowest cross-section flow rate of the fluid sent from the inlet of the channel with a flow rate of 300 µl was determined in conical design. This indicates that there will be more interaction with the surface compared to other patterned arrays. In Project 2, The purpose of this project is to create a biosynthetic neuron-on-a-chip to reproduce the activity of neuronal function. Neurons are the main important units of the nervous system and brain. The target of neurons is to receive sensory input from the outside world and send motor commands to the muscles. They are also responsible for converting and transmitting electrical signals in every step that takes place in this cycle. Neurons communicate with electrochemical signals. Therefore, electrical and chemical events must occur together for the communication of two neuron cells. It transmits a neuron signal through the axons to the dendrites of other neurons to which it connects via the axons called synapses. Long Term Potentialization is a process in which synaptic connections between neurons are strengthened by frequent activation. LTP is thought to change the brain in response to experience, thereby providing a mechanism underlying learning and memory. In the process of learning, nerve cells, the basic computing units of any nervous system, are thought to exhibit digital and analog properties. Alpha-synuclein(α-syn) proteins are of high importance to sustaining LTP in the brain. In this thesis, the most suitable platform for communication between two yeast cells and the passage of α-syn proteins through channels is optimized and designed. It refers to nerve cells in the computer environment by yeast cells in the simulation program. A channel that enables the communication of two yeast cells was designed and these yeast cells were placed in the traps located at the entrances of the channels. The activating agent was sent to produce α-syn of yeast cells in the A channel. Αlpha-synuclein protein, which is synthesized from yeast cells in the A channel, has passed through the channel and attached to the NDMA receptor in the other yeast cell in the B channel. Then, LTP was provided by activating the α-syn protein bound to the NDMA receptor in a balanced manner with Ca^+ions. Irregularity in the ratio of protein Ca^+ and α-syn prevents the formation of long term potentiation and causes Parkinson's disease. Optimization studies were carried out in microfluidic chip design. The number of channels along with the microfluidic chip, the width of chamber A and B, the width of the communication channel, the distance between communication channels, the length of yeast cells chamber, the length of yeast cells communication channel, the inlet-outlet radius of chamber A and B were determined. As a result of these determinations, it was observed how each parameter affects diffusion. The greater diffusion indicates that the amount of α-syn protein passes more from chamber A to chamber B. It was also observed that some parameters started diffusion earlier. Therefore, it enabled more yeast cells to interact. Computer modeling and simulation were applied as a very useful tool for improvements in the design of microfluidic chip geometry, as well as for the optimization of the technological and functional parameters. In this thesis, COMSOL Multiphysics, which is the most used in microfluidic systems, is used in two projects for microfluidic chip design and simulations within the designed chip.
Design and simulation of micromixers for efficient antigen-antibody binding

(Graduate School, 2023-04-04) Ertemür, Simge Naz ; Kızıl, Hüseyin ; 513201023 ; Nanoscience & Nanoengineering

Microfluidic systems have gained more attention, especially in the past decade due to technological improvement in this area. They have become an important tool for clinical analysis and spread to other areas to be used for different purposes. Microfluidic systems have been utilized for various applications such as drug delivery, clinical diagnostics, biomedical engineering, etc. They offer substantial advantages including low reagent consumption, fast analysis, and high sensitivity of detection. Fluid flow in the microchannel is laminar and dominated by molecular diffusion due to small Reynolds numbers of the fluids resulting in insufficient mixing. Enhanced mixing is required in most applications dealing with biological samples. To improve mixing, generally active or passive micromixers are used. Active micromixers require external energy sources such as dielectrophoresis, and electrokinetic disturbance which make the fabrication complicated while passive micromixers do not require any external energy sources. For this reason, passive micromixers are preferred due to their ease of fabrication and simple operation. In this study, in order to enhance mixing, passive micromixers with varying geometries have been designed and a fluid flow pattern has been simulated using COMSOL Multiphysics software. Antigens and antibody-modified magnetic beads were fed through two different inlets with varying channel geometries. The inlet channel geometry for the magnetic beads is expected to result in the formation of vorticities and disturbance of the fluid flow, causing the dispersion and rotation of the magnetic beads, which will help increase the binding efficiency of antigens onto the surface of antibody-modified magnetic beads. Moreover, the proposed micromixer geometries will cause hydrodynamic interactions between antigens and antibody-modified magnetic beads when they flow through the channel which enhances mixing. According to COMSOL simulation results, serpentine, and convergence-divergence type, micromixers resulted in good mixing of different fluids. To verify simulation results experimentally, some of the designed microfluidic systems giving the best simulation results were fabricated and tested.
Designing, developing and using the anode of a microbial fuel cell by containing PDMS,carbon nanotubes and graphene

(Graduate School, 2022) Şakar, Elif Hazal ; Trabzon, Levent ; 713487 ; Nano Science& Nano Enginering Programme

In the last few years, micro/nano electromechanical systems are an area that has been rising very rapidly and attracting a lot of attention of researchers. Microbial fuel cells, which is also a subject covered by the MEMS/NEMS field, is also a very interesting field of study. The reason for this is the increase in energy consumption in the world with each passing day and the search for a renewable energy source has become a necessity. The anodes and cathodes of MFCs are intended to operate at both low cost and high efficiency. Graphene, carbon nanotubes and PDMS, an organic polymer, can be counted among the materials that are widely used in this field and are trying to be developed. In our own study, we used these materials as hybrid nanocomposites. In addition to the MFC anode electrode studies in the literature, we tried to obtain electrical conductivity with lower cost and higher efficiency. In order to achieve these goals, we designed a special pattern in the anode electrode, which will increase the electrode surface area in a way that the microbial flora can be used most effectively, ensure the efficient adhesion of the microbial flora, and to attract electrons with the highest capacity, and we have produced it by photolithography. In order to find the optimum electrode, PDMS/MWCNT/GNP hybrid nanocomposite samples were produced at different ratios. In addition, the effect of treating the produced anode electrodes with sulfuric acid on the electrical conductivity was investigated. As a result of our production, we analyzed the anode electrodes with a few characterization devices that are widely used in nanotechnology studies. As a result of the analyzes made, it was observed that the produced electrodes had a very successful electrical conductivity when compared with the examples in the literature. It has been observed that the treatment with sulfuric acid causes a very successful increase in electrical conductivity within a certain treatment time. As an important result, it has been observed that the electrical conductivity can vary greatly depending on the mixing ratios and the type of nanofiller used. As a result of this experimental study, it has been concluded that the electrodes produced at low cost and at certain rates have successful electrical conductivity compared to previous studies in the literature.
Development of antibacterial coatings on titanium based biomaterials

(Lisansüstü Eğitim Enstitüsü, 2022) Aydoğan, Dilek Teker ; Çimenoğlu, Hüseyin ; 723039 ; Nanobilim ve Nanomühendislik

Since the average human life is getting longer, research on long-lasting and biocompatible biomaterials has become more common. A biomaterial is a material that can replace any damaged tissue or organ and therefore, it is in continuous interaction with body fluids. There are various biomaterials for different application areas. The main issues to be considered are the mechanical properties, design, and biocompatibility of the developed biomaterial. Metal and metal alloys are the most frequently preferred biomaterials and they have been used as hip, knee, and dental implants for many years. These biomaterials are also expected to show superiour biocompatibility, corrosion and wear resistance, along with non-toxicity. Especially the long-term stability of orthopedic and dental implants depends on the bonding properties at the implant-bone interface and being free of any post-operative infections due to the implant features. Titanium and titanium alloys stand out among other metallic implant materials (such as stainless steel and cobalt-chromium alloys) with their excellent mechanical properties, biocompatibility, low densitiy, high corrosion and wear resistance. The most important feature that separates titanium from the other metals is the natural oxide film layer on its surface. Even though, this stable, dense, and continuous layer provides corrosion resistance and biocompatibility to the material, but, its ability to bond to bone is quite weak. In addition, due to the toxic effect caused by alloying elements that can be released from some titanium alloys (such as Ti6Al4V), titanium alloys may fail in long-term implant applications. For this reason, numerous surface treatment methods are used to enhanced the surface features of titanium and its alloys. Micro-arc oxidation (MAO), also called plasma electrolytic oxidation, is a convenient technic that is used to produce ceramic coatings on titanium, aluminum, magnesium, and their alloys. With this method, it is possible to get thick, porous, firmly attached ceramic coatings on the surface of titanium and its alloys. In addition to these, antibacterial oxide coatings can also be obtained by adding appropriate antibacterial agents into the electrolyte used during the process. The ability to coat materials with complex shapes, using environmentally friendly chemicals, and being a cost-effective process are the prominent advantages of this method. In the scope of this study, the formation of bioactive and antibacterial oxide coatings on the surface of titanium and its alloys was carried out via MAO process. In the first chapter of the thesis, it was aimed to produce multi-layer bioactive and antibacterial coatings on the commercially pure titanium (grade 4 quality, Cp-Ti) surface, which is frequently preferred in biomedical applications, by applying the MAO process. For this purpose, samples were subjected to a base electrolyte (which is containing calcium acetate hydrate (Ca(CH3COO)2.H2O) and disodium hydrogen phosphate (Na2HPO4)) during the MAO process. To obtain antibacterial properties on the coating surface silver acetate (AgC2H3O2) was added into the base electrolyte (the amount of silver (Ag) on the coating was measured as 4.6 wt.%). After the MAO process, a multi-layered oxide coating consisting of TiO2 (dense rutile-anatase phases) on the inner layer, and biocompatible compounds such as hydroxyapatite (HA) and calcium titanate (CaTiO3) just above oxide layer was obtained. It was observed that MAO treated samples in the base electrolyte formed biomimetic apatite structure faster in the simulated body fluid (SBF), as well as showed higher antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria. It has been determined that the addition of AgC2H3O2 to the base electrolyte increased the antibacterial activity of the samples without sacrificing bioactivity. In the second chapter of the thesis, optimization of AgC2H3O2 amount which had been added into the base electrolyte was studied in order to avoid toxic effect of Ag without sacrificing the antibacterial effect. The MAO process has been conducted in the base electrolyte containing Na2HP04 and Ca(CH3COO)2.H2O and AgC2H3O2 was added at different concentrations. Samples treated with an electrolyte containing 0.005 mol/L AgC2H3O2 concentration showed poor antibacterial activity against S. aureus bacteria, while samples treated with the electrolyte containing 0.001 and 0.002 mol/L Ag concentrations was determined strong antibacterial activity. Based on these results, considering the possible toxic effect of Ag, 0.001 mol/L AgC2H3O2 concentration into the base electrolyte is sufficient for MAO process. It was determined that used optimum AgC2H3O2 concentration into the base electrolyte caused 1.14% Ag on the oxide coating surface after MAO process. Cell culture experiments were performed using SAOS-2 (a human primary osteogenic sarcoma cell line) to understand the effect of the amount of silver measured from the coating surface on the cell. As a result, it was observed that the amount of Ag determined in the oxide coating did not prevent cell growth however retarted it and also showed high antibacterial efficiency against S. aureus bacteria. In the third chapter of the thesis, after determining the optimum amount of AgC2H3O2 concentration in the base electrolyte containing Ca(CH3COO)2.H2O and Na2HPO4 in the previous section, the biological properties of the oxide coating formed in the MAO process using Ti6Al4V alloy were investigated by biofilm formation and cell culture experiments. After adding 0.001 mol/L AgC2H3O2 to the base electrolyte during the MAO process, it was determined that there was 0.76 wt.% Ag on the oxide coating surface. It was observed that the alloying elements in the Ti6Al4V alloy effect the structure of the oxide coating formed by the MAO process conditions. The low amount of Ag measured from the coating surface was explained by the precipitation of Ag particles mostly around the pores of the thick TiO2 layer, and the formation of a thick HA layer on it. The presence of Ag particles between TiO2 and HA layer effected Ag release behavior in simulated body fluid (SBF). Compared with Ag-free coatings, the presence of 0.76 wt. % Ag in oxide coatings exhibited antibacterial activity to some extent against Streptococcus mutans (S. mutans) bacteria and did not adversely effect the proliferation of SAOS-2 cells. However, in order to obtain enhanced antibacterial efficiency, higher amount of silver must be incorporated into the MAO coating. In the fourth chapter of the thesis, the structural features, Ag release behavior and bioactivity of HT treated oxide layer with different amounts of Ag nanoparticles formed via MAO process on Ti6Al7Nb alloy have been investigated. While MAO process was applied in the base electrolyte (containing (Ca(CH3COO)2.H2O) and (Na2HPO4)) with and without the addition of AgC2H3O2 to obtain oxide layer, HT treatment was performed in an alkaline solution (pH = 11) at 230 ºC to improve bioactivity. After the MAO process, HA structure with a low degree of crystallinity and TiO2 layer containing rutile and anatase structures was formed on the surface. Nano-sized Ag particles were detected on the coatings formed over Ag incorporated oxide coatings. Moreover, higher AgC2H3O2 concentration in the base electrolyte caused a higher number of Ag nano-particles in the MAO coating. Afterwards, application of the HT treatment fabricated an 1-2 m thick exterior surface layer that is composed of nano-rod TiO2 and hexagonal HA crystal morphologies on oxide surface and increased degree of HA crystallinity. When samples treated with MAO and MAO+HT are compared, it was observed that HT treatment not only accelerated biomimetic apatite accumulation on Ti6Al7Nb alloy but it also eliminated the negative effect of Ag, which delayed the apatite formation on the MAO coatings. In addition, unlike the oxide coatings formed with MAO, HT treatment considerably reduced the amount of Ag released from the oxide coating into the SBF solution. As a result, thick, microporous and multi-layered oxide coatings containing bioactive components have been successfully produced on the surface of titanium and its alloys, which are frequently prefered in implant applications. Generally, various additives such as ions or particles can be introduced into the electrolyte to fabricate antibacterial oxide coatings with biocampatible properties via MAO process. Within the scope of the thesis, studies have shown that oxide coatings which were fabricated using different amount of Ag agent in the base electrolyte exhibited antibacterial efficiency on bacterial cultures and bioactive components support the bioactivity. Especially in obtaining antibacterial coatings, the importance of Ag agent amount in the base electrolyte has been demonstrated by antibacterial tests. In addition to the MAO process, when MAO process is combined with HT treatment, it is possible to fabricate highly bioactive surfaces without obtaining multi-layered coatings on the substrates. Moreover, Ag agent has been introduced into the oxide coating to give antibacterial properties to the surface. The Ag agents and their amounts is still one of the biggest concerns for health. In the future studies, the living body applications (in vivo) will guide the evaluation and development of short and long term effects of TiO2 based bioactive and antibacterial coatings fabricated with MAO process and HT treatment.
Development of interlayer based thin-film nanofibrous composite membranes adjusted by functionalized carbon nanotubes for effectual water purification

(Graduate School, 2022-01-20) Arabi, Seyedehnegar ; Gökoğlu Zeytuncu, Bihter ; 513191019 ; Nano Science and Nano Engineering ; Nano Bilim ve Nano Mühendislik

Drinkable water supply is one of the fundamental human prerequisites all over the world. Due to the population expansion, the changes in the global climate, and water degradation, The requirement for freshwater increases with time around the world. Based on the reported calculations, except for 2.5% of existence global water, which is classified in the potable water range for humans, 70% of the remaining freshwater (FW) is frozen. Due to recent reports, more than 700 million people worldwide have not been accessed clean water. Ascribed to the severe FW demands, which have been observed in some developing countries and sub-Saharan African countries, the water treatment technologies must be enforced in these overwhelmed countries. Nanoscience and nanotechnology are other novel solutions to water treatment technology problems. Ascribed to nanomaterials properties, including high aspect ratio, reactivity, adjustable pore volume, hydrophilic, hydrophobic, and electrostatic interactions, they have been utilized in numerous types of applications. Multiple types of batteries, optics, fuel cells, sensors, electrics, thermoelectric devices, pharmaceuticals, and cosmetics are some industries that have used nanomaterials to improve their products. Moreover, nanotechnology has been performed in economically unconventional water sources, resolving contaminant-free water for humans, and suggesting many solutions to alleviate needs with regard to reducing scarcity or removing contamination. For example, there are filters that remove pesticides from drinking water using nanochemistry. At the same time, due to the multidisciplinary feature of membrane technology and essential advantages of membrane science technology, such as being clean energy, the ability of energy-saving, high-quality products, and system versatility, it has been applied in multiple applications. The power of membrane technology to replace other purification systems, including distillation and ion exchange systems, has been distinguished as other membrane technology's benefits. Furthermore, because of the forward osmosis (FO) and nanofiltration (NF), membranes' excellent features such as energy conversion, low-cost procedure, and high water recovery ability have received much more attention in wastewater treatment, water purification, and brackish water desalination over the last decade. The electrospinning device generally consists of a high voltage power supply, a supply unit, and a grounded collector. The feed solution is sent to the feed end by a pump. An electric field is created by a high-voltage power supply connected to the supply terminal. As the applied voltage increases, the electrical forces overcome the viscoelastic forces of the solution at the feed end. After a critical voltage, a jet formation is observed at the supply end. The bubbler solution diffuses in the electrical field and accumulates randomly on the collecting plate in microscopic diameter fibers. The solvent in the solution evaporates before or after the fibers are collected in the container. Among the factors affecting the nanofiber production by electrospinning method are the type of polymer to be obtained, conductivity and dielectric properties, the solvent used, the viscosity of the feed solution, the distance between the feed unit and the collector, the feed rate (flow rate), the voltage used. More than 100 polymers can be electrospinning, and the most preferred among these polymers in nanofiber membrane construction are; polyacrylonitrile (PAN), poly(ethylene oxide) (PEO), polystyrene (PS), Nylon-6, poly(vinyl alcohol) (PVA), poly(ε-caprolactone) (PCL) and polycarbonate. PVA is a water-soluble, non-toxic, and biocompatible polyhydroxy polymer with high chemical resistance and thermal stability among these polymers. It is known that PVA easily interacts with other organic and inorganic materials. However, PVA's applications are limited due to its hydrophilic nature. Therefore, it must be modified to minimize dissolution, mainly used in aqueous applications such as filtration and adsorption. Chemical crosslinking of PVA nanofibers with dialdehydes, dicarboxylic acids, or dianhydride is advantageous in becoming insoluble in all solvents and increasing their thermal and chemical properties. Polymeric thin-film composites are essential types of compounds applied in various practical applications, including surface coatings and modifications, adsorption and immobilization, membrane technologies, and low surface energy interfaces. Also, the inherent internal concentration polarization (ICP), which causes osmotic driving force's decline, is another major problem of conventional TFC membranes which has been challenged for several years. Moreover, biological fouling is another disadvantage that limits the conventional TFC membranes' performance in multiple usages. Due to the biological fouling of TFC type membranes, microorganisms and micropollutants, which require reproduction, easily stick to the membrane's surface and cause a significant reduction of FO membranes' stability and durability. In order to break the trade-off between permeability and selectivity of TFC membranes and obtain membranes with balanced permeability and rejection performance and excellent durability, triple-layered thin film composite (TFC) forward osmosis (FO) membranes fabricated by introducing an interlayer on the porous electrospun membranes before interfacial polymerization (IP) procedure. Introducing an interlayer on the electrospun substrate overcomes the conventional TFC membranes' limitations and causes synthesizing controlled polyamide (PA) layer and improving the IP process. Carbon nanotubes (CNTs), cellulose nanocrystal, and cadmium hydroxide nano-strands are some of the nanomaterials that have been introduced as an interlayer in TFC types of membranes. The adopted interlayers develop the barrier selective layer's structure and control the IP procedure. Due to the CNT's ideal characteristics, such as large specific surface area (SSA) and excellent mechanical stability, CNTs are distinguished as superior nanomaterials that have been performed as interlayers in TFC membranes. Triple-layered TFC membranes with CNT interlayer enhance the PA layer formation with defect-free and ultrathin structure and promote the membrane's permeation ability, even rejecting monovalent and divalent ions. The membranes were utilized in this research are thin-film nanofibrous composite membranes with hydrolyzed multi-walled carbon nanotubes (MWCNTs) as an interlayer. First of all, MWCNTs had been acid-treated in the presence of sulfuric (H2SO4) and nitric (HNO3) acids. Secondly, the different amounts of hydrolyzed MWCNTs were dispersed in the distilled water using ultrasonication and then introduced as an interlayer onto the porous polyacrylonitrile (PAN) electrospun membranes by vacuum filtration procedure. Finally, TFC membranes were prepared to utilize the IP procedure. In this study, MPD and TMC solutions had been performed as aqueous and organic phases to begin the IP proceeding. The prepared membranes had been tested in dead-end filtration systems to investigate the membranes' performance in salt rejections. Also, these interlayer-based TFC membranes had been applied in the dye removal from industrial wastewaters and compared to the conventional TFC type of membranes in their filtration performance.
Development of microfluidic based single cell capturing systems for early detection of diseases

(Fen Bilimleri Enstitüsü, 2020) Altınağaç, Emre ; Kızıl, Hüseyin ; 650348 ; Nanobilim ve Nanomühendislik Ana Bilim Dalı

It is known that cancer cells in the bloodstream are quite low compared to other cells in the blood. Microfluidic based systems have been studied for diagnosis, follow-up of the disease and new drug tests to be performed on this disease. A microfluidic based system with two successive regions for separation and analysis has been developed. In the first region, the target cell type is differentiated from a complex mixture containing multiple cells by dielectrophoresis, which allows an insulating particle to be polarized under an electric field. Since different cell types can be polarized at different rates under the same electric field, this method allows the separation of the cells from each other under suitable conditions. In this study, a microfluidic system consists of two consecutive regions, namely the separation and analysis regions are demonstrated. In the first region, the target cell type is separated by dielectrophoresis from a complex cell mixture. The target cells collected in the first region are continuously transferred to the second region and are captured in a single cell array formation at the hydrodynamic capture stations placed on the measuring electrodes. Impedance analysis was performed to establish a platform for detection and drug screening. While both regions were integrated on a single chip in the final device, each region were examined separately during our study. The results of impedance analysis obtained from different cells based on different medium conductivities with a frequency range of 0.1kHz – 500kHz are presented here. We recorded impedance measurements at stations where cells were individually captured before and after cell entrapment. Experimental results are divided into cases where the conductivity of the medium is higher and lower than the cell conductance. Overall magnitude of impedance shift is significantly higher when the medium conductivity is lower than the cell conductance. When all results are evaluated, it can be seen that depending on the target cell type, an optimum medium conductivity and frequency range can be selected so as to obtain the measurement result with the highest sensitivity. A microfluidic cell culture platform, named as organ-on-a-chip in the literature, has been increasingly studied over the last few years to mimic tissue and organ-level physiology, containing a membrane with a continuous and porous structure inhabited by living cells, and with microfluidic channels to mimic the mechanical effects and to supply the necessary nutrients. These platforms create tissue and organ environments that are not possible with traditional 2D or 3D culture systems, and enable real time imaging and analysis of biochemical, genetic and metabolic activities of living cells. In this project, present fabrication techniques of microfluidic devices are used for the fabrication of organ-on-a-chip platforms. The tissue structure was imitated by coating a single-layer cell on the upper and lower sides of the membrane in the structures of the renal chip tubules and lung alveoli on organ-on-a-chip platforms. The cell viability was characterized by MTT test and the cell viability was maintained by providing oxygen, carbon dioxide and nutrient exchange under incubation conditions by means of nutrient medium flow provided into the upper and lower channels, and the barrier property of the cell tissue was measured by electrical resistance (TEER) measurements. The viability of the renal tubules cultured in the microfluidic system between 0-48 hours was recorded by MTT assay. TEER results showed that the tight-junctions of cell tissue were different under static and dynamic conditions in the kidney-on-chip systems. The results obtained by MTT test to measure cell viability were in agreement with TEER and the viability of kidney cells was higher in 48 hours under dynamic conditions compared to static conditions. With the successful culturing of two different cell types under static conditions in lung-on-chip systems, their viability and cell barrier resistance values were recorded by TEER measurement for 0-48 hours. The results obtained by MTT test and TEER measurements showed that lung cells under shear stress and mechanical stress had higher viability than cells under static conditions.
Development of nano-alloyed CdTeS quantum dots via two-phase synthesis method

(Graduate School, 2022) Kestir, Sacide Melek ; Ünlü, Caner ; 737886 ; Department of Nanoscience and Nanoengineering

The 20th century was called as the golden age for the science since the significant discoveries that is going to affect human life was made in that century. The science around that time opened the new gate to the mysterious world that humankind had been take advantage of it without even realizing but they had never been able to discover. The humankind had tried to explore and investigate the unfamiliar materials which came from especially nano scale at that time. The new characterization techniques like X-ray lead to finding of properties of these novel materials which is not visible to human eye. They have only from 1 to 100 nm dimensions, however; their surface and physical properties are way better than bulk materials that no one can argue. Therefore, since then the interest to the nano science have been increased day by day. And this new world has named as nanomaterials for last 30 years. The main cause for unique properties of nanomaterials comes from the confinement of electrons which bulk materials don't display. As a result of the confinement, discrete energy levels are formed due to interaction between valance and conjugation band under Bohr radius. On other words, it can be said that electrons have no freedom to move in nano dimension, their motion is confined. One type of the quantum nanostructures are zero-dimensional materials which named after restriction in all dimensions. Quantum dots which is zero-dimensional nano structure displays exclusive physical properties like high photoluminescence, wide adsorption and narrow emission. QDs in other words semiconductor nanocrystals, which synthesized for the first time in 1981 by Ekimov and was took its name in 1984, used 2000 years ago by Romans and Greeks and due to its discrete energy levels in their structure, they also are named as artificial atoms. Besides the discrete energy levels in QDs, high surface-to-volume-ratio properties makes them ideal candidate from diagnostic to photovoltaic cells. Their adsorption wavelength is broad from infrared to ultraviolet which means different size of the QDs can be excited with the same wavelength. At the same time, they have narrow emission wavelength that are altered with QDs' size and composition. In other words, QDs can emit different kind of wavelength with the same composition by changing the size. They are generally composed of II-VI and III-V elements from periodic table. Among these properties, QDs are more stable and brighter than organic dyes. As the properties of these nanomaterials have been understood, the attraction for these materials have increased especially last 20 year. There has been more attempt to use it for treatment, diagnosis of illness and for the solar cells to increase efficiency of photovoltaic cells. According to application area, different types of QDs, having diverse size, composition and structures, can be desired which is achievable with the help of the different types of the fabrication techniques. However, the main challenge part is to fabricate them effectively under the mild conditions without giving harm to the nature. Today, the manufacture methods are divided into two parts: top-down and bottom-up. Both have its own advantages and drawbacks. Bottom-up methods mean the self-assembly of the atom or molecules to constitute desired structure. Self-assembly is the key part of these methods. Method starts with the nucleation and goes on with the self-assembly and when the free energy reaches the maximum level, the production finishes.
Development of novel aflatoxin B1 biosensors by carbon nanotube integrated microfluidic systems

(Graduate School, 2024-05-08) Arslan Okutan, Nagihan ; Trabzon, Levent ; 513132008 ; Nanoscience and Nanoengineering

Aflatoxin B1 (AFB1), which contaminates food and feed via molds, is carcinogenic to humans and animals. In addition to adverse effect on human and animal health, it results in product losses due to the difficulties of decontamination. When negative health consequences and product losses are studied economically, it is clear that they result in significant losses and issues for developing countries. To preserve human and animal health, as well as prevent product and economic losses, AFB1 contamination must be regulated at all phases of the food production system, from field to fork. Effective risk assessment and risk management techniques are required to prevent food contamination. Risk assessment requires scientific methodologies. The first stage is to use scientific procedures to detect, measure, or analyze. Traditional AFB1 detection/analysis methods such as microbiological cultivation, chromatographic analysis and ELISA test involve complicated laboratory procedures and difficult, long processes requiring expert personnel. It is expensive because it requires a lot of sample and chemical solvents, and causes environmental pollution. It forces our country to be dependent on foreign sources due to the import of analytical devices. It is conceivable to reduce such long and complex procedures into a chip and realize the lab-on-chip (LOC) concept with the ultimate technology of microfluidic systems. Today, with the advancement of microfluidic technology, it is possible to actualize such long and complex laboratory operations by miniaturizing them to a chip, thereby bringing the notion of laboratory-on-chip (LOC) to reality. In our country, it is vital to profit from the advantages of such advanced technology in items with competitive power in exports, such as olive oil. Where several governmental entities have taken measures toward quality improvement and branding by resolving existing problems, and comprehensive R&D studies must be conducted to address such issues. The submitted thesis describes the development of an integrated microfluidic system that extracts, detects, and quantifies AFB1 in olive oil by combining microfluidic technology and nanotechnology. The integrated system will include three modules: a paper-based microfluidic AFB1 biosensor (µPAD), a PDMS-based microfluidic mixer connected to µPAD, and a syringe pump system for introducing AFB1-treated olive oil and extraction solvents at specific times and volumes. The aim of the thesis is defined as; i. Creating AFB1 detection areas using different techniques with the help of hydrophobic materials on cellulose-based filter paper, ii. Functionalization of MWCNTs by immobilizing antibodies that will specifically identify the target AFB1, iii. Integration of detection areas of functionalized MWCNTs, iv. Production and optimization of PDMS-based microfluidic mixers, v. Integration of microfluidic biosensor and mixer with syringe pumps, vi: Extraction of AFB1 from olive oil with microfluidic mixers, vii. Validation of the microfluidic biosensor and quantitative measurement of extracted AFB1 samples. The first stage of the thesis is to create detection areas and channels on filter papers with the help of various hydrophobic materials. For this purpose, different fabrication techniques were applied for each hydrophobic material. When variables such as ease of manufacture, cost, analysis in which the biosensor will be utilized, and required chemical solvent resistances were considered, it was decided to continue experimental research with the wax dipping approach. The second stage is to transform the detection areas created on paper into biosensor surfaces where we can perform AFB1 detection and quantitative analysis. At this stage, nanotechnology methods were utilized. Multi-walled carbon nanotubes (MWCNT) are used in biosensors because they improve detection sensitivity by increasing surface area and provide an ideal surface for the immobilization of biological components such as antibodies. For biological detection, MWCNT surfaces must be biologically functionalized and distributed uniformly in a dispersant to ensure homogenous integration in detecting areas. Chemical alterations must be made to the surface structures of MWCNTs to achieve both goals. Due to strong van der Waals interactions, MWCNTs disperse as bundles in water, which limits their biosensor applications. MWCNTs are distributed homogeneously in water due to the carboxyl (-COOH) and hydroxyl (-OH) groups formed as a result of the treatment of MWCNTs with chemicals such as acids or peroxides. Additionally, these groups enable antibodies to bind to the MWCNT surface. With this aim, MWCNT solutions were prepared with HNO3, H2SO4 + HNO3, H2O2, H2O2 + H2SO4 to observe the formation of -COOH and -OH groups, and the FTIR method was used to determine if the appropriate functional groups developed on MWCNTs as a result of certain time and temperature applications. According to FTIR measurement results, acid oxidations were continued with HNO3, which provides the formation of -COOH groups. XRD measurements were performed for structural analysis. In the XRD spectrum of MWCNT functionalized with HNO3, the MWCNT crystal plane with added carboxyl groups was seen at 260 and the MWCNT characteristic crystal plane was seen at 430. The presence of the -COOH group was examined by XPS measurements. According to the results obtained from the elemental compositions, the Oxygen (O) ratio increased as a result of the treatment of MWCNTs with acids. Oxygen originates from -COOH groups formed as a result of reactions with acids on the surface. Nitrogen (N) was seen as a result of antibody immobilization, indicating that protein was added to the system. The increase in Oxygen (O) ratio along with Nitrogen (N) shows that protein structures are immobilized on the surface. In other words, the antibody to which AFB1 will specifically bind is immobilized on the MWCNT surface. As understood from the morphological characterizations, there was no significant change occurred in MWCNT morphologies after HNO3 treatment, and their structures were not damaged. With antibody immobilization, a beaded appearance like a cover was formed on the MWCNT surface. This shows that the protein layer bound to MWCNTs was formed and the immobilization was successful. A paper-based biosensor (µPAD) was successfully created by dispersing antibody-functionalized MWCNTs in water and integrating them onto the paper detection areas obtained in the first stage via the drop casting technique. In order to obtain sensitive results in food contamination analyses, the contaminant must be extracted from the food matrix. The other part of the thesis work is AFB1 extraction from olive oil. PDMS-based microfluidic mixers were fabricated for pre-teratments. Separation and mixing abilities were observed with various designs such as straight, sunflower, 1800 and 2400 degree bend angles, 200, 500, and 1000 µm channel widths. After COMSOL simulations and experimental optimizations with different microchannel designs, it was decided to fabricate microfluidic mixers with sunflower geometry. PDMS based mixers were created via UV litography and soft litography techniques. PDMS was preferred as the second surface instead of glass due to its flexibility and ease of micromixing. The last phase of the thesis consists of detection and quantitative analysis studies with µPADs. In AFB1 detection studies, it was observed that AFB1 could be detected at a concentration of 1 ng/mL under the FL microscope, thanks to the FL dye-labeled secondary antibody. Quantitative studies performed with a FL microscope were carried out with AFB1 standard solutions. Standard solutions prepared in the concentration range of 0.01-100 ng/mL were dropped onto the µPAD surface and examined under a microscope. Because clear results could not be obtained from MWCNT alone, silver nanoparticles (AgNP) were introduced to the system during the functionalization stage. Thanks to AgNPs, quantitative measurements were made by image analysis and a calibration graph was created. The lowest detectable concentration was determined as 0.1 ng/mL. Resistance measurements (four point probe) were made on MWCNT surfaces with the same standard AFB1 solutions and a calibration graph was created. The lowest detectable concentration was determined as 0.01 ng/mL. More precise measurements were made with resistance measurements. Both types of studies have shown that µPADs have two different linear working ranges: 0.1-1 ng/mL and 1-10 ng/mL. Microfluidic mixers integrated with syringe pumps were used for pre-teratment studies. After AFB1 spiked olive oil samples passed through the microfluidic mixer, quantitative resistance measurements were conducted. The biosensor recovery rates ranged from 91 to 97%. FL spectroscopic measurements in AFB1 standard solutions served to validate the results. Linear operating range and recovery rates are likewise within acceptable levels, according with the literature. The integrated system has high sensitivity AFB1 detection capacity. It has the potential to be used in every field where AFB1 detection is legally required. When the lowest quantities found are studied, it is clear that detection may be accomplished with a sensitivity below the legal limits. It will be cheaper compared to other technologies due to the materials used, it will reduce the economic burden required by the analysis since it is sufficient to use less chemicals and samples, and it will provide an environmentally friendly technology due to less waste chemicals. AFB1 can be used not only in the laboratory environment but also without the need for expert personnel because it is portable and simple to use. It is a modular analysis system that will enable on-site detection. In addition, it is a domestic product and domestic patent technology that will reduce our country's import dependence on analytical devices and technologies. Due to the combination of microfluidic technology and nanotechnology, the system has many differences and advantages compared to academic studies, patents and commercial products that serve similar purposes. It has the potential to turn into a domestic and high value-added product that has the power to create its own market in the national and international arena if it is patented and commercialized with its originality.
Development of SAW sensors coated with metal organic framework and borophene for detection of Covid-19

(Graduate School, 2023-06-05) Albay, Maide Miray ; Zayim, Esra ; 513191025 ; Nano Science and Nano Engineering

The rapid and accurate detection of COVID-19 biomarkers is critical for the early diagnosis and effective treatment of the disease. In this study, surface acoustic wave (SAW) biosensors coated with metal-organic framework (MOF) and borophene layers were developed to detect COVID-19 biomarker gases, including isopropyl alcohol, n-butyraldehyde, acetone, and ethyl butyrate. In addition, the gas measurement system includes ethanol and n-hexane, which are already present in human exhaled air. The objective of this study is to investigate the response of different MOFs and borophene to these biomarker gases and to determine the optimal sensing material for COVID-19 biomarker detection. Seven different materials are coated onto SAW sensors using the drop-casting method as sensing layer. These materials include borophene, MIL-101 (Fe), MIL-101 (Fe)-Borophene, MIL-125, MIL-125-Borophene, MOF-5, and MOF-5-Borophene. They are selected based on their distinct metal components and their potential for detecting COVID-19 biomarker gases. When choosing MOFs, it is preferred to use MOFs that have same organic ligand but a different metal in their center. It is aimed at comparing metal effects and other results related to metal effects. Sensing molecules are characterized using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and Brunauer-Emmett-Teller (BET) analysis. SEM is employed for analyzing the thickness and roughness of coating films on SAW sensors. To examine the sensor's frequency change, a gas measurement system in TÜBİTAK MAM is employed. This system is for the preparation of gas mixtures at different concentrations and humidity levels, which are then sent to the surface of the sensors at room temperature with a constant flow rate. In addition to measuring the change in resonance frequency of the transducer device, the electrical conductivity of the surface is simultaneously measured under related gases to determine the influence of electrical conductivity on sensor performance. Results are processed using MATLAB to read, compare, and perform principal component analysis (PCA). The results of the gas sensing experiments show that the MOFs have a better response to the COVID-19 biomarker without borophene. MOFs also exhibited good selectivity for the target gases. This suggests that these sensors could be used for selective detection of COVID-19 biomarkers in a mixed environment. Keywords:surface acoustic wave(SAW) sensors, metal organic frameworks (MOFs), volatile organic compounds(VOCs), biomarkers, COVID-19
Fabrication and characterization of novel membranes for battery separator applications

(Graduate School, 2023-05-26) Ahmetoğlu, Ubey ; Kılıç, Ali ; 513201024 ; Nanoscience and Nanoengineering

With the prospering industry of electrical mobility, the need for high-performance batteries and energy sources is on the rise. The demand on efficient and safe batteries has exponentially increased. In general, batteries consist of three main critical components; anode, cathode and a separator. While anode and cathode are the active parts in charge and power generation, battery separators are the non-active insulative part. They are a porous structure that allows the passage of ions back and forth while they are made of inherently electrically insulative materials that prohibits the contact of the two poles preventing any short circuit possibility. Battery separators can be made of several materials and substances and carry several key properties. They can be made of any porous insulative material with defined pore size and porosity for their intended application. Along their porous structure, they should carry high chemical stability, strong integrity, and stability under elevating temperatures. Since there are various reactions occurring inside a battery which may lead to an increase in the cell temperature, several approaches are used to fabricate battery separators with high thermal stability and flame retardancy. Among these approaches, coating the separator with inherently flame-retardant materials is a common method. Sodium alginate, as a natural polysaccharide, that shows significant flame retardancy performance when crosslinked with calcium. Cross-linked calcium alginate is reported to exhibit a limiting oxygen index (LOI) of 34. Several polymers are used to fabricate the battery separator. Ultra-high molecular weight polyethylene (UHMWPE) is widely used in battery separator applications due to its high mechanical strength and chemical stability. Film casting is a process widely used to fabricate battery separators. In the wet process film casting, UHMWPE is melt-mixed with a low molecular weight diluent (also called porogen) and casted through a film die before its conveyed into stretching and extraction steps to obtain final porous membrane. Another type of common separator is the nanofiber-based. They can be fabricated via several methods including centrifugal spinning, where a rotor is ejecting the polymeric solution into fibers while rotating at very high speeds. The aim of this thesis is to fabricate lithium and sodium ion battery separators with different fabrication methods and enhance their thermal performance by coating them with calcium alginate. Film casting and centrifugal spinning processes were used to obtain two different membrane structures from two different polymers. In the film casting process, UHMWPE was mixed with paraffin oil (PO) then melted and extruded through a twin-screw extruder (TSE). 30% UHMWPE, 70% PO, and 1% antioxidant mixture was prepared. The temperature of the 6 heating zones and die was held at 130, 140, 150, 160, 170, 180, and 180℃ respectively. The screw rotating speed was held constant at 35rpm. The melt blend was cast through a stripe die with a thickness of 3 mm. The obtained sheets were hot pressed at 180℃ and 8 tons of load for 8 minutes then cooled down to room temperature. The final film thickness obtained was in the range of 200-400μm. Optimization experiments were conducted on the samples to study the effect of different stretching ratios, the importance of extraction step order, the effect of the constrained and nonconstrained uniaxial stretching, and the effect of heating distance between the sample and the stretching machine. It was found that the extraction of the oil after stretching led to a smaller and more uniform pore size in comparison to bigger pores formed when the oil was extracted before stretching. Heating of the samples in the stretching machine was done with the open system using thermal irradiators. Distances of 13.5, 16.5, and 19.5cm were studied. Heaters caused the film to melt fastly and close the pores formed at close distances while at 19.5cm the heating wasn't enough to initiate any pores. The films are then stretched with a custom-made uniaxial stretching machine, where pore formation is initiated. Two stretching ratios were applied; 2×1.5 and 4×1.5. Higher stretching ratios showed the closure of pores. The optimum parameters were found to be a 1.5×2 constrained stretching ratio with a 16.5 cm heating distance and 110℃ heating temperature. After that three Samples (S1, S2, and S3) were fabricated and hot pressed into three thicknesses of 280, 200, and 280μm. These samples are then stretched and annealed to obtain samples of three final thicknesses of 40, 60, and 80μm. Finally, these samples are immersed in n-hexane to extract the oil and obtain the desired porous structure and the final membrane. These membranes are then put in a coin cell configuration and tested for sodium ion (Na-ion) battery separator performance. The ionic conductivities of S1, S2, and S3 samples are 0.09, 0.48, and 0.04mS/cm2 respectively. The S2 sample showed better performance in comparison to other samples due to its higher porosity and uniform pore distribution. Nanofibrous membrane on the other hand was fabricated from thermoplastic polyurethane (TPU) by centrifugal spinning process. TPU was dissolved in dimethylformamide (DMF)/acetone mixture and spun into nanofibers. Optimization of the process was done by altering the polymer concentration, solvent ratios, needle diameter (gauge), and rotating speeds. The optimum nanofibers were obtained at 10% TPU dissolved in a 2:1 DMF/acetone ratio with 30G needle diameter and 13,000 rpm rotating speed. Obtained nanofibers were treated with sodium alginate which was then crosslinked with calcium chloride (CaCl2). After Calcium Alginate (Ca-alg, CA) treatment, the samples were hot pressed at 120℃ and 8 tonnes of load for 2 minutes. Treatment with CA enhances the thermal performance of the separators. The obtained coated nanofibrous membranes were then put into coin cell configuration with 1M LiPF6 and 1M NaClO4 electrolytes and its performance was measured. These membranes were tested for sodium ion (Na-ion) and lithium-ion (Li-ion) batteries. The nanofibrous membranes exhibited significantly better performance when compared to the commercial Celgard 2500 polypropylene (PP) separator. The ionic conductivities of the neat TPU, pressed TPU, 0.5 TPU, and 2 TPU were 0.23, 0.67, 0.17, 0.16, and 0.05 mS/cm2 respectively. The coated samples exhibited significantly larger ionic conductivity numbers and lower resistance values in comparison to the commercial PP separator. In full cell configuration, where anode and cathode are used, the samples exhibited the same trend with neat TPU performing better than other samples. The ionic conductivities of the full-cell samples were 1.53, 0.19, 0.05, and 0.03 mS/cm2 respectively. The drop in the ionic conductivities of the samples can be referred to as the effect of coating the samples which leads to pore closure. This led to the domination of the diffusion phenomena in the samples which was demonstrated by the straight line in the Nyquist plot. In terms of thermal performance, significant enhancement was achieved. On the other hand, when these samples were examined for Li-ion separator tests, the ionic conductivities of Neat TPU, 0.5 TPU, 2 TPU, and PP separators were 0.10, 0.21, 0.09, and 0.07mS/cm2 respectively. The 0.5 TPU sample showed the best performance and proved that calcium alginate can enhance the chemical performance of the separator. The coated samples showed 0% shrinkage in comparison to 63% and 100% shrinkage of the neat TPU and commercial samples. The samples also showed significant fire retardation when exposed to flame source. A comparison between the condition of the samples after 1 and 10 seconds was recorded. Neat and pressed samples melted directly within the first seconds, while the treated 0.5 TPU and 2 TPU samples kept their integrity. 0.5 TPU sample showed marks of burning and its color started turning into brownish while the 2 TPU sample kept its initial state even after 10 seconds. The obtained results showed the high potential calcium alginate carries in battery applications. Studies to enhance the ionic conductivities of the calcium alginate can be conducted and better integrating methods can be proposed.
Fabrication of multi-component superparamagnetic nanoparticles and magnetic heating performance for hyperthermia cancer therapy

(Graduate School, 2021-02-16) Çetin, Ayşesimay ; Kılıç, Ali ; 513171012 ; Nanoscience and Nanoengineering

Nowadays, cancer has become a major public health problem worldwide. It is known that 19.3 million new cancer cases and approximately 10 million cancer deaths occurred worldwide in 2020 alone. The TUIK 2020 report, the cancer is in second place with 80,186 people in Turkey ranking of causes of death. Traditional methods such as chemotherapy, radiotherapy and surgery do not give highly successful results in cancer stages that have spread in the body. These treatment methods carry fatal risks by damaging healthy tissues depending on the treatment method in the patient. For this reason, various treatment methods have been developed that are expected to affect only damaged tissue. Hyperthermia is one of the methods developed for this purpose. Multilayer functional superparamagnetic nanoparticles (NPs) are used in the method, which can be used in medical imaging and treatment applications. With these NPs, it is tried to develop the use of optical and magnetic methods for both diagnosis and treatment of cancer. Thanks to a dielectric shell coated on the NPs, its agglomeration can be prevented, and thanks to an organic shell coated on it, its properties such as biocompatibility and stability can be increased, as well as various molecule adhesion capabilities for treatment purposes can be given to the surfaces of the NPs. In addition to the magnetic properties of these NPs, it will be possible to heat them with the near infrared (NIR) laser to be applied due to their surface plasmon resonance properties. Basically in this method; It is aimed to; (a) reach the denaturation temperature (42ºC) of the cancer cells by applying an alternative magnetic field that will affect only the tumor area, and (b) the malignant cells are destroyed by heating while the other healthy tissues remain stable. In this way, the side effects that occur in traditional methods are tried to be minimized. The two most important factors determining the use of magnetic NPs in hyperthermia therapy are; (a) the applied NPs must have a high ability to heat the cancerous tissue to the desired temperature and (b) heating should be limited only to the cancerous tissue. These two factors can be achieved by having excellent magnetic properties that can reach the target temperature by using a small amount of NPs in the target tissue. For this reason, the type of magnetic NPs used and their magnetic heating performance are of great importance. Studies on various NPs such as Fe3O4, MnFe2O4 are quite common, but it becomes impossible to compare the experimental results due to the different methods and different environmental conditions determined for NPs fabrication in the studies. Therefore, more research is needed to make hyperthermia treatment available. In the thesis, in the first part, Fe3O4, MgFe2O4, MnFe2O4 and SrFe12O19 NPs were synthesiszed as cores. Later, their outher surface was first coated with SiO2 layer, functionalized with amination, then decorated via Au NPs and consequently the outer surface of overall NPs will be coated via PEG. After each coating, the NPs have been characterized using FTIR, SEM and EDX. Heating process was carried out under AMF, using induction generator, in water and in agar according to the rate calculation of 0.1% (v/m) of the produced NPs. According to the results of the heating tests, among all samples, SrFe12O19 NPs showed the lowest and MgFe2O4 NPs showed the highest heating performance among all samples in the tests where different core types were compared. According to the heating results comparing the different coating stages, the aminated NPs gave the fastest warming result among the other coating stages. Comparing different coating steps, PEG coated samples gave the slowest heating result in the heating results. In addition, the heating performance of gold-coated samples, which is the previous coating step from PEG, is very close to that of PEG coated samples and gave the second lowest performance. As a result, our study has shown that different coating stages and NPs differences change the heating performance of superparamagnetic NPs. Although there are many studies of magnetic NPs in the literature, the effects of different types of magnetic NPs on the heating performance of different coating stages of these NPs were compared under standardized laboratory conditions. It is possible to say that this study, which is carried out with easily accessible and economical laboratory materials, is illuminating for future researches related to the subject.
Fabrication of nanostructured metal oxide materials and their use in energy and environmental applications

( 2020) Çalışır, Mehmet Durmuş ; Kılıç, Ali ; 634370 ; Nanobilim ve Nanomühendislik Ana Bilim Dalı

Metal oxides are considered to be the most vital material class and they show unique chemical, physical and electronic properties when produced on the nanometer scale. In this context, metal oxide nanomaterials are of increasing importance in many industries and are used in applications such as sensors, medical technologies, energy, water treatment, and personal care products. In this thesis, the fabrication of nanostructured metal oxide materials and their use in energy and environmental applications which have strategic and vital importance are focused. The optimization of process parameters for the production of metal oxide nanostructures via industrial-scale production methods and application-oriented modifications of the properties of metal oxides via controlling their size and composition have been realized. Solar energy is an environmentally friendly technology that allows direct energy production from the sun. Perovskite solar cells (PSCs) have been studied intensively in the last decade and they constitute the energy leg of this thesis. In this context, the effects of metal oxide nanomaterials on perovskite cells performance were investigated. The performance of planar and mesostructured PSCs was compared, while all the experimental studies for the production of highly-efficient PSCs were given in detail. The mesoporous architecture allows the deposition of denser perovskite films than planar architecture due to the high porosity. Though higher efficiency was expected due to effective absorption of incoming light, XRD results showed that PbI2 - perovskite conversion in the mesoporous structure was more difficult. The average efficiency of the cells produced with mesoporous architecture was 15.07 %, which was just 0.9 % higher than the planar one. As can be deduced from the absorbance curves and IPCE analysis, this is because of the mesoporous structure showing more absorbance in the 400-600 nm wavelength range resulting in more photocurrent. However, due to the small difference in efficiency and fewer steps in the planar architecture, it was found more viable for industrial scale-up. Air pollution is one of the most critical environmental problems today, and filtration is one of the practical solutions to remove the pollutants, especially particulate matter within the air. However, exhaust gases might be at high temperatures and require high-temperature resistant filter materials. The use of ceramic-based, fibrous filter elements in filtration applications will enable the production of highly efficient filters with high-temperature stability. In this context, SiO2 nanofibrous mats were produced from sol-gel based solutions via centrifugal spinning (CS) and solution blowing (SB) methods. According to results, centrifugally spun SiO2 fibers were found more flexible where fibers have diameters between 1 and 1.5 microns. Solution blown silica fibrous mats consisted of thinner fibers but have denser bead and droplet defects. Besides, due to the fibrous mats obtained by SB had a dense-packed structure it showed more shrinkage during heat treatment. XRD results show that all fibers have an amorphous SiO2 structure after heat treatment at 600°C. According to the porosity analysis, the solution blown and centrifugally spun SiO2 samples had the lowest pore diameters of 5.2 and 10.5 microns, respectively. Moreover, the effects of SiO2 precursor solution concentration on spinnability in the CS method, the diameter of SiO2 fibers, and filtration efficiency were investigated. Contrary to expectations, the average diameter of the fibers has been found to decrease with increasing precursor concentration a result of reduced viscosity of the spinning solution. While all the produced fibers are incredibly flexible, the highest filtration efficiency (43.35 Pa pressure drop and 75% particle capture efficiency) was obtained from the sample that produced from 15 wt.% TEOS added solution. Due to excellent thermal stability and high mechanical performance of centrifugally spun SiO2 fibrous mats they have the potential as filter materials for hot air filtration applications. Photocatalyst-based purification techniques emerge as a solution for recovery of used water. While the studies focused on the development of photocatalyst material with visible light activity, there is also a need for the development of photocatalyst geometries that can be easily separated from treated water. Although nanoparticulate morphology offers high surface area, it is difficult to remove them from treated water. On the other hand, TiO2 is one of the most studied materials among the photocatalysts due to its high photocatalytic activity, photostability, chemical inertness, and low-cost. TiO2 fibers were fabricated via CS and subsequent calcination methods. The effects of precursor concentrations on fiber diameter, surface area, and photocatalytic activity were investigated. Results showed that the fiber diameter was increased from 0.65 to 1.2 µm with increasing precursor content. The calcined fibers consisted mainly of anatase and also a minor amount of rutile phases. PVP used as the carrier polymer for precursor solution also behaved as a nitrogen source for TiO2 fibers during calcination. The slight shift of peaks in XRD, the presence of nitrogen in XPS spectrum and EDX mapping, and the enhanced visible-light photocatalytic response were pieces of evidence for in-situ N-doped TiO2 NFs. Besides, nanoparticles (P25 NPs) were added into the spinning solution to increase the surface area by producing nanoparticle in nanofiber structure, and it was also used as a reference sample. According to the results of photocatalysis tests, the surface area is the dominant factor for photocatalysis under UV illumination and the optical bandgap is the critical factor for the tests performed under visible light illumination. Moreover, recycle analysis showed that fibrous photocatalysts were easily separated from the treated water. In this regard, the fibrous TiO2 was emphasized as the best visible-light photocatalyst, losing only 14% of its degradation performance after the 3rd use. The effect of Al and Li doping on the crystallinity, fiber diameter, optical bandgap, and photocatalytic activity of TiO2 fibers was investigated in the last part of this thesis. Al and Li doped N-TiO2 fibers were successfully produced via CS method and followed calcination. N- TiO2 showed a fiber diameter of 0.54 µm while Al- and Li-doped N- TiO2 had a diameter of 0.94 and 1.15 nm, respectively. While the crystal structure of N-TiO2 transformed from major anatase and minor rutile phases to the only anatase in the case of Al- and major rutile and minor anatase phases in the case of Li-doped N-TiO2. Additionally, band gap values were calculated as 3.00, 2.94, and 3.14 eV for N- TiO2, Li- and Al-doped N- TiO2, respectively. For the photocatalysis tests conducted under UV-light, the most efficient sample was the nanoparticulate TiO2 due to its high surface areas, while all-fibrous structures showed similar activities, which were nearly two times higher than the activity of nanoparticulate TiO2 under visible-light.
Formation and structural properties of water induced structures at graphene/mica and graphene/CrxO/glass interfaces

(Graduate School, 2021-10-08) Novruzov, Orkhan ; Gürlü, Oğuzhan ; 513171019 ; Nano Science and Nano Engineering ; Nano Bilim ve Nano Mühendislik

Water behavior at interfaces has great importance. Especially molecularly thin layer water or nanoconfined water. Nanoconfined water properties are different from bulk ones. Studying nanoconfined water properties have fundamental importance in biology, material science, nanofluidics, tribology, and corrosion. Nanoconfiment materials are carbon nanotubes and layered two-dimensional materials or Van der Waals crystals. In this thesis, we studied water interaction behavior with graphene/water/CrxOy/glass and graphene/mica systems. For this purpose, we needed the following devices: Optic microscope with the isolated system, PVD system, graphene heater, and materials like CVD-grown graphene, muscovite mica, soda-lime glass, and chromium granulates. Firstly, we started with graphene/water/CrxOy/glass system. We did thermal evaporation of chromium using PVD system that was assembled in our laboratory. As a substrate, we used soda lime microscope slide glass(INTROLAB). Chromium thin-film on glass samples was produced. The thickness of thin-film chromium was varied. We transferred CVD-grown graphene onto chromium thin-film glass with the wet transfer method, then annealed it in a tube furnace around 450°C degrees under atmospheric ambient conditions for approximately 40 minutes. As soon as annealing finished we quickly transferred produced sample into a container full of silica gels to preserve from environmental humidity. We reduced humidity within enclosed boxes in which an Optical light microscope stayed for study samples under controlled humidification. We took optic data before, during, and after the humidification process. Secondly, our second system for research was graphene/water/mica. Again as in the graphene/water/CrxOy/glass system, we used CVD-grown graphene and V2grade muscovite mica(Ted Pella). Using scotch tape we cleavage mica several times then CVD-grown graphene was transferred onto it using the wet transfer method. We preserve graphene/mica samples in a container full of silica gels. We studied them with two methods: First under the optic microscope in the isolated box and second using the graphene heater. We reduced humidity to 9% in the isolated box using silica. In the case of the graphene heater, we managed to heat up nearly 200°C. We observed fractal in graphene/CrxOy/glass system but due to non-homogeneous deposition of chromium fractal formation was inconsistent. In case of graphene/mica system observation of de/rewetting process was not possible even though we reduce humidity. The graphene heater was functional, the reason that we couldn't use it was a poorer resolution of the graphene/mica system. Otherwise, observation de/rewetting graphene/water/mica with the optic microscope is challenging.
Graphene oxide/calcium titanate composite preparation for humidity sensing by quartz crystal microbalance

(Graduate School, 2022-09-06) Demirtaş, Zeynep ; Benli, Birgül ; 513201037 ; Nanoscience and Nanoengineering

Humidity measurement has been taking attention since 1900s because of the fact that it is used in various aspects from weather forecasts to food and human safety, agricultural processes to mineral processing facilities. Therefore, there has been a growing requirement and extensive research on designing humidity sensors that are rapid, cost-effective, and highly sensitive. Although various methods have been developed, the Quartz Crystal Microbalance (QCM) is a very promising candidate, as it has excellent sensitivity to changes in mass with a nanogram level of detection and, an extensive measuring range. In addition, QCM sensors are stable and reliable in mild operation conditions and can be developed with low-cost. However, the quality and the properties of sensors are highly dependent on the additional sensitive layer. Thus, an additional sensing layer on the surface of QCM electrodes is required to improve the sensor performance including selectivity, sensitivity, response/recovery time and stability. The sensing layer is one of the most important parameters that affects sensing properties of QCM. In literature, there are numerous studies for using different single component containing materials as sensing layer for humidity measurement. On the other hand, the combination of two or more materials, composites, is necessary to obtain improved sensing properties. For humidity sensing, the composite material can be made either with an additional porous material to enhance the interactions with water molecules or with an additional humidity sensitive material to increase the overall humidity sensitivity. Graphene oxide, a two-dimensional material with excellent physical properties, is an excellent candidate for humidity measurement because of the hydrophilic groups on its surface that ensure the adsorption of water molecules. In addition, the use of an additional nanostructured material as calcium titanate can improve the sensitivity by increasing the surface area to volume ratio. In this thesis, the preparation and coating properties of graphene oxide/calcium titanate composite-based material was investigated for the first time in literature. GO was obtained from graphite powder by using a modified Hummer's method. Calcium titanate particles were synthesized by sol-gel method. After the production of two different materials separately, they blended to obtain the composite material. Characterization analyses were performed for optical, structural, and morphological properties of graphene oxide, calcium titanate and graphene oxide/calcium titanate composite materials. The obtained results confirm that a successful production of the composite material was achieved.
Hydrometallurgical recovery of platinum from catalytic converters

(Graduate School, 2022) Otlu, Derya ; Kadırgan, Figen ; 737027 ; NanoScience & NanoEngineering

With the developing technology and the improvement of environmental protection laws, the consumption amount of platinum group metals (PGM) is increasing significantly. Over the last decade, these metals have found more use in industrial applications and with the growth in the world population, the consumption amount of products that use these metals has also increased. In particular, the automotive industry has been the area where metals in this group are most needed, due to the increasing production capacity and the emission regulations that are being tightened day by day. In this study, the properties of platinum group metals, their usage area, applications in catalytic converters and recycling methods were investigated. Afterwards, using a scrap catalytic converter, Pt was recycled from the catalyst and the parameters which affect the recycling efficiency were optimized. During the selection of the recovery method and its operation, the minimum damage to the environment was taken into consideration. As a result of the experimental studies, the dissolution of Pt was achieved by heat treatment of the leach solution prepared with 4.5M HCl (14.4%), 12.5% H2O2, 40/1 solid-liquid ratio at 75 °C for 90 minutes, with a recovery rate of 91.12%. In the precipitation experiments, the reduction of Pt to the metallic form is obtained with 0.079 mol NaBH4 which was mixed with the solution prepared under the best leaching conditions. Also, this solution was heat treated at 65 ℃ for 60 minutes, and the precipitation efficiency of 97.88% was achieved. As a result of the serial experiment, within the scope of the thesis, a simple and environmentally friendly hydrometallurgical method was developed for the recovery of Pt from catalytic converters; that have completed their useful life. Ultimately, 89.19% of Pt was recovered by optimizing the experimental parameters in the dissolution and precipitation experiments.

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