LEE- Nano Bilim ve Nano Mühendislik-Yüksek Lisans

Bu koleksiyon için kalıcı URI

http://hdl.handle.net/11527/19416

Gözat

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.
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 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 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 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.
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.
Improvement of electrical and photocatalytic properties of boron-doped ZnO nanorods and synthesis design optimization by taguchi approach

(Graduate School, 2024-01-29) Tabak, Eray ; Benli, Birgül ; 513201031 ; Nanoscience and Nanoengineering

Today, increasing environmental pollution affects the whole world. One of the most important pollutions among environmental pollution is water pollution. Water pollution seriously threatens living life. With the developing technology, clean water resources are decreasing, and water resources are polluted with industrial and domestic wastes every day. Today, traditional methods are used for water treatment. However, these methods are not able to provide adequate response to water treatment due to low efficiency for small-sized pollution and secondary pollution. Therefore, applications of photocatalysis offer an effective opportunity among advanced oxidative methods; in this study, innovative photocatalyst structures have been developed. Boron doped ZnO nanorods were successfully synthesised by hydrothermal method and Boron doping has led to enhancements in its photocatalytic and electrical properties. Boron doped ZnO nanorods were grown in two stages. In the first stage, since dipole forces will be effective for growth, the thin film called seed layer layer on the glass surface was coated with the surface spin coating method. Then, with zinc nitrate dehydrate and hexamethylenetetetraamine added in equal molar amounts, nanorods were grown on the glass with seed layer at 90 °C for 3 hours. X-ray diffaraction (XRD), UV-Vis spectrometer, FT-IR, DC electrical analysis (I-V), AC electrical analysis, characterisation by Scanning electron microscopy (SEM) and photocatalytic analysis by UV-A 366 nm light were also performed. Then, Taguchi experimental design method was used to determine the best conditions for selected parameters such as pH, pollutant concentration, time, additive amount and to calculate the effects between each other. The XRD results indicate that boron has successfully integrated into the structure. Also, pure and boron doped ZnO nanorods grew in wurtzite structure and the crystal sizes were confirmed by SEM images. As a result of FT-IR analysis, it was shown that the peak belonging to B-O, B-O-B bonds increased with the increase in doping. It was proved that the band gap intervals calculated as a result of UV-Vis spectrometry analysis decreased with boron doping. Electrical analyses showed that the electrical conductivity increased with increasing boron doping. As a result of all these analyses, electrical conductivity increased from 0.03 μA for pure ZnO to 1.9 μA for 10% boron doped ZnO. With the increase in surface defect, the band gap decreased with the increase in conductivity, boron doping was proven to increase the number of electrons and it was thought that their photocatalytic activity should increase. As a result of photocatalytic tests, it was shown that the efficiency increased with boron doping. When we compare the numerical values of the rate constants, under the same conditions, the 1% B doped sample has a 94% higher rate than the pure ZnO sample for pH 4. For pH 7, the 3% B-doped sample has a 36% higher rate than pure ZnO, and finally for pH 10, the 7% B-doped sample has a 194% higher rate constant. Moreover, the effect of pH was discussed. It was observed that boron doped ZnO nanorods had better photocatalytic efficiency for each pH range and concentration. As a result of the calculated rate constants, 3% boron doping for 2x10-6 M concentration, pH 7 showed the best result with a rate constant value of 0.00856 min-1. Finally, optimized parameters for pH 4, concentration 2x10-6 M, time 90 min and doping amount 7% were determined by Taguchi method. As a result of ANOVA analysis, the model was proved to be 85% fit.
PEDOT:PSS-CB based interdigitated supercapacitors

(Graduate School, 2023-01-31) Altun, Enes Can ; Yavuz Karatepe, Nilgün ; 513191008 ; Nano Science and Nano Engineering

The globe will meet the need for energy in many different ways as global energy consumption keeps rising. In order to enhance dependable and renewable energy and balance supply and demand, energy storage systems are now being expanded. Although significant progress has been achieved in the development of high-performance fuel cells and li-ion batteries, their applicability in many industries has been constrained by their poor power density and high maintenance requirements. Because they have qualities that conventional energy storage devices lack, supercapacitors have recently attracted a lot of attention. A key feature of energy storage devices is that they deliver high power density while also having a low charge-discharge rate. They offer high power density at the same time as a low charge-discharge rate, which is an important characteristic of energy storage devices. In addition to many renewable generation methods for energy production, the importance of storing this energy and using it later is obvious. Today, energy storage devices are used in automobiles, telephones, and all areas where energy is used. Frequently used storage devices can be supplied with Li-ion batteries, supercapacitors, and capacitors. The usage area of traditional capacitors has decreased rapidly from the past to the present. For this reason, studies between batteries and supercapacitors have been increasing rapidly in recent years and countries with high energy needs are investing in these areas. Batteries, especially li-ion batteries, are the most frequently encountered energy storage devices, from phones to automobiles. Although high energy capacity is its most important feature, different energy storage has been sought due to its limited lifetime, inability to withstand high cycles, lack of high power density and not being environmentally friendly after the end of its useful life. In response to this need, research on supercapacitors has brought to mind the idea of whether they can replace batteries. Supercapacitors are preferred due to the high number of cycles, high energy and power density, and flexible working areas. Besides the types of supercapacitors, there are also different configurations. Although sandwich-type supercapacitors are generally used, interdigitated supercapacitors have been used recently with the development of different production methods. Although conventional sandwich-type supercapacitors have relatively high capacitance, they have high ion transport resistance and low active surface area. Therefore, the power density is low. The production of interdigitated supercapacitors can be fast, wearable, flexible, and small in size. In on-chip applications, interdigitated supercapacitors can be applied to any surface in the form of a film. This study, it was tried to give general information about supercapacitors. It is aimed to operate devices that do not require high energy by connecting high-capacity comb supercapacitors in series. PEDOT:PSS polymer material was used as the electrode material due to its semiconductor and excellent electrical performance. PVA gel-based xxii material was preferred as the electrolyte. As a characterization method, supercapacitors were analyzed in detail using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) methods. To obtain interdigitated supercapacitors, patterns were created on the electrode surfaces by laser etching method. For this purpose, a laser with a 15 Watt power and a wavelength of 450 nm was used. To be able to process the patterns precisely, the laser was mounted on a plotter and the patterns were automatically processed by means of software. Since the conductivity of the PEDOT:PSS material used as the electrode material is not at a sufficient level, first of all, some materials were doped in order and the conductivity amount was aimed to reach the desired level. The doped materials are DMSO, ethylene glycol/methanol, and carbon black (CB), respectively. As a result of the added materials, PEDOT:PSS achieved the desired high conductivity. The glass surface with dimensions of 25mmx25mm was thoroughly cleaned with alcohol and water, and then the PEDOT:PSS-CB material, which was prepared beforehand, was applied to the surface by the drop-casting. Then, it was dried at 65 ⁰C for 2 hours and a thin film was obtained on the glass surface, and the coating process was completed. Then, a comb structure was formed on this surface by the laser etching method and the electrode was made ready for use. A copper current collector is affixed to the prepared electrode. Then, these current collectors are covered with insulating tape so that they do not come into contact with the electrolyte. Then, the prepared PVA-based gel electrolyte containing 6M KOH was poured onto the comb structures with the help of a syringe. The prepared energy cell is placed in a closed container so that the electrolyte does not dry out. In this way, both single and eight different samples were prepared. It is aimed to reach high voltage values by connecting the eight samples prepared in series. The operating range of the single cell is -1 V +1V and the operating range of the octa-series cell is determined as -6V +6V. As a result of the study, eight cells connected in series and a red LED bulb worked for 1 minute.
Point-of-care detection of respiratory tract infections using a novel PCR kit with gold nanoparticle-mediated dna polymerase

(Graduate School, 2023-06-21) Elmas, Mert ; Karataş Yazgan, Ayten ; 513201017 ; Nano Science and Nano Engineering

Respiratory tract infections (RTIs) are common and can cause a wide range of illnesses, from mild colds to severe pneumonia, bronchitis, and other respiratory diseases. RTIs are a significant burden on public health, with high morbidity and mortality rates, particularly in vulnerable populations such as the elderly, children, and immunocompromised individuals. However, current diagnostic methods for respiratory tract infections (RTIs) are often time-consuming and require specialized equipment and trained personnel, resulting in long turnaround times and delays in treatment. In order to address this challenge, we developed a novel PCR kit for the detection of SARS-CoV-2, Influenza A virus, Influenza B virus, Respiratory Syncytial Virus (RSV) A/B, Human Adenovirus, Human Rhinovirus and Streptococcus pyogenes named Respiratory ID Panel 2 (RIDK-2), that uses gold nanoparticles to enhance DNA polymerase activity, thereby improving the sensitivity and specificity of RTI detection. In this study, we designed and optimized the gold nanoparticle-enhanced PCR kit and validated its analytical performance compared to same RT-qPCR kit produced without golden nanoparticles (AuNPs), including preliminary limit of detection (LoD), LoD, wet and in-silico inclusivity, wet and in-silico exclusivity, and stability studies. The kit demonstrated superior analytical performance, with high sensitivity and specificity for detecting target RTI pathogens mentioned above. The RIDK-2 has a turnaround time under 1 hour without the need of nucleic acid extraction with a LoD of 250 cp/mL for research samples prepared using reference materials and the kit showed no cross reactivity. The rapid turnaround time and accuracy of the gold nanoparticle-enhanced PCR kit make it a valuable tool for the timely diagnosis of RTIs, reducing the risk of intensive care unit admission and death. Furthermore, stability studies showed that the kit without gold nanoparticles could be stored at room temperature for up to 6 hours without significant loss of performance, while the gold nanoparticle-enhanced PCR kit was stable for up to 72 hours, making it suitable for use in clinics, including pediatric clinics, where specialized equipment and refrigeration may not be readily available. According to the analytical performance studies the kit's sensitivity and specificity was found as 99.74% and 99.61%. These findings suggest that the gold nanoparticle-enhanced PCR kit has the potential to significantly improve the management of RTIs, thereby enhancing patient outcomes and reducing healthcare costs.
Polyamide synthesis for reverse osmosis membrane and substrate optimization

(Graduate School, 2024-02-02) Arslan, Büşra ; Trabzon, Levent ; Yücedağ Taşdelen, Çiğdem ; 513201027 ; Nanoscience and Nanoengineering

Because of growing population, global warming and increasing industrialisation, our need for clean water is growing. Water treatment systems can be used to treat industrial wastewater, sewage, etc., as well as sea water, and turn it into drinking water. There are many systems for purifying water. Nanofiltration, microfiltration, reverse osmosis, forward osmosis, and electrodialysis are the most common. 60% of the world's water purification systems are RO. In addition, the use of polymer membrane is common. In general, the RO membranes work under the press, which is able to change the pressure from 60 bar up to 100 bar. Reducing energy consumption is the most issue in RO research due to the high pressure. The cost of RO systems can be reduced by reducing the amount of pressure applied. When the amount of pressure applied is reduced, cost effectiveness is achieved. Reverse osmosis is the process by which water is desalinated using membranes that separate the dissolved components in the feed water but allow the water to pass through. In the reverse osmosis membrane process, as water passes through a membrane by the solution-diffusion mechanism, solutes are retained by electrostatic forces in their size and dissolved ions on the membrane surface. Polymeric RO is composed of three layers. The firs layer, a thin film, which is made up of polyamide separates the components like salt ions. The second layer, a porous polysulfone support layer, directs the flow of water. The final layer, a nonwoven PET layer, increases mechanical strength. Polysulfone carrier layers can be produced by electroblowing, electrospinning or solution blowing. The support layer produced by nanofiber production methods generally has a more porous structure. The nanofiber support layer leads to useful way by which the water flux conveniently pass through, contrast to other support layer types. This results in a high water flow and a reduction in the required applied pressure. This situation reduced energy concuption. The supporting layers made by the phase inversion method have a low percentage of the surface voidand the void size on the surface is relatively small compared to the others support layer types made by nanofiber production methods. The advantage of the phase inversion method is that is more suitable for industrial production. The reasons for the selection of nanofiber production by electro-blow spinning method are that the fiber optimization process is relatively easier and it is also efficient in mass production.
Preparation and characterization of nanofibers for energy applications

(Graduate School, 2023-03-16) Cihanbeyoğlu, Göktuğ ; Yanılmaz, Meltem ; 513181005 ; Nanoscience and Nanoengineering

Renewable energy researches have been intensively increased to address the problems arising from massive usage of fossil fuels including serious environmental problems. Burning fossil fuels emits carbon dioxide, enhances radiative forcing and leads to global warming. By using renewable energy sources, it is possible to mitigate negative effects of fossil-based economy, reduce the dependence of fossil fuels and decrease emission of greenhouse gases. Development of energy storage systems which are capable of storing electrical energy harvested from renewable sources is important. In this regard, secondary batteries have been the center of attention due to efficient storage and delivery of electrical energy. Lithium-ion batteries (LIBs) have been used in wide range of portable electronics and electric vehicles (EVs), owing to long working life, large energy-conversion efficiency, and being environmentally-friendly. Moreover, sodium-ion batteries (NIBs) have attracted great attention because of high abundance and low-cost of sodium resources. NIBs present opportunities for potential applications in large-scale grid energy storage. Electrode materials play an important role to determine electrochemical performance of batteries, including energy density, life time, operation current densities. In LIBs, metal oxides or phosphate materials (e.g. LiCoO2, LiNiCoAlO2 and LiFePO4) and graphite-based materials are used as the cathodes and anodes, respectively. In NIBs, carbon-based anodes and phosphate-based cathodes have driven the industrialization of the NIBs. The electronic and ionic conductivity are two crucial factors presenting great influence on the electrochemical performance, that are usually altered through doping, control of materials size and introduction of conductive substrate or additives (e.g. conductive metal, polymers and carbon-based materials). Carbon nanofibers (CNFs) have been used in many applications such as sensors, energy storage and biomedical applications owing to high electronic conductivity and chemical stability of CNFs. Performance of carbon nanofibers are influenced by the physical and chemical properties of nanofibers. Furthermore, morphology, porosity and specific surface area are important properties for several applications including energy storage and sensors. There are several techniques to produce nanofibers including chemical vapor deposition, catalytic synthesis, arc discharge and electrospinning. Controlling surface area and porosity is vital considering the performance of CNFs. In this study, polyacrylonitrile (PAN) nanofibers were produced via two commonly used nanofiber production techniques; electrospinning and centrifugal spinning. The morphology of the polymeric nanofibers was studied by using SEM. Moreover, heat treatment was applied in air and the inert atmosphere to fabricate carbon nanofibers and porous carbon nanofibers. The effect of production technique on the morphology and chemical structure was investigated via SEM and XRD studies. Electrospun PAN/PS nanofibers showed beads on string morphology due to low viscosity of the spinning solution while uniform fibers without defects were obtained by using centrifugal spinning technique. Centrifugally spun PAN nanofibers have rough surface while PAN nanofibers with smooth surface was obtained by using electrospinning technique. PCNFs derived from centrifugally spun PAN/PMMA nanofibers had rough surface with porous structure and XRD analysis proved the amorphous structure of PCNFs. Germanium has been the center of interest due to its enormous conductivity and Li diffusivity. Germanium is a promising anode material for sodium ion batteries owing to high theoretical capacity as well. However, it suffers from large capacity losses during cycling because of the large volume change and loss of electronic conductivity. Herein, centrifugally spun binder free N, S doped germanium@ porous carbon nanofiber (N,S doped Ge@ PCNFs) anodes first were synthesized using a fast, safe and scalable centrifugal spinning followed by heat treatment and N, S doping. The morphology and structure of the resultant N, S doped Ge@ PCNFs were investigated by scanning electron nanoscopy, transmission electron nanoscopy, EDX mapping, Raman spectroscopy and X-ray diffraction, while electrochemical performance of N,S doped Ge@ PCNFs was studied using galvanostatic charge-discharge tests. The results demonstrate that a nanostructured Ge homogeneously distributed on highly porous carbon nanofibers. Moreover, N, S doping via thiourea treatment is beneficial for the lithium and sodium ion kinetics. While interconnected PCNFs buffer volume change and provide fast diffusion channels for Li ions and Na ions, N, S doped PCNFs further improved electronic conductivity and thus led to higher reversible capacity with better cycling performance.

Gözat

Başlık ile LEE- Nano Bilim ve Nano Mühendislik-Yüksek Lisans'a göz atma

Sayfa başına sonuç

Sıralama Seçenekleri