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Preparation of indium tin oxide thin films and investigation of hydrogen post-treatment effect
The development of optoelectronic devices including solar cells, liquid crystal displays, touchscreen panels and electrochromics has required a broad application of transparent conductive oxides (TCOs) as an essential component. TCOs come into prominence due to their outstanding properties such as 80% and more transmittance in the visible region of the solar spectrum and sheet resistance lower than 300 Ω/sq. Among TCOs, tin doped indium oxide (ITO) films are the most extensively preferred thin films owing to their high transmittance (~90 %) at 550 nm and low sheet resistance between 20-100 Ω/sq. Using vacuum based techniques such as magnetron sputtering can be very efficient to obtain low sheet resistance, however, this causes a dramatic increase in the production cost. Since ITO is the most extensively used transparent conductive electrode and it will have a huge market share in the near future; it is very obvious that the optical and electrical properties of the ITO films should be enhanced by means of simple and cost-effective preparation techniques. The aim of this thesis was the preparation of ITO thin films by scalable and low cost solution based methods with improved optical and electrical properties. For this purpose, thin films prepared by spin coating technique were subjected to post-treatment process to decrease sheet resistance and increase surface smoothness without causing any change in optical transmittance and crystalline structure. Effect of different parameters such as In:Sn ratio, concentration, temperature, number of deposition and post-treatment with hydrogen to sheet resistance, transparency, surface characteristics and crystalline structure were investigated. The properties of thin films were characterized by four probe measurement set-up, UV-visible spectroscopy (UV-Vis), scanning electron microscopy (SEM) and X-ray diffractometer (XRD). It has been found that 7 times deposition of 0.5 M solution including In:Sn with the ratio of 90:10 was the optimum process condition when the films were annealed at 500-600°C in air. For all samples, transmittance were measured in between 80 and 92 % at 550 nm and minimum sheet resistance was measured as 350 Ω/sq after post-treatment. Post-treatment provided a growth in crystalline size, distinct grain boundaries, and homogeneous particle distribution without influencing cubic crystalline structure due to XRD and SEM results. Subjecting the ITO films to 10 % H2 containing Ar medium at 300 °C for 3 hours was found as the most efficient process condition for post-treatment and as a result of that, approximately 70% efficiency was achieved on the reduction of sheet resistance without affecting the transmittance of the thin films.
Design, analysis, simulation and optimization of a MEMS Lorentz force magnetic field sensor for biosensing of biowarfare agents
The alarming terrorist attacks via the exploitation of bacteria and viruses in the history of mankind have set concerns globally and led the governments to identify and recognize biological warfare agents such as bacteria and viruses for taking preventative action. Hence, fast detection and precise identification of these agents have been attributed as key strategies for biodefense globally. In the interest of biological warfare agent sensing, sensitive and optimized tools/sensors are needed that are capable of quantifying the response of physical attachments of the biological agents into measurable values for their detection. For this purpose, MEMS based cantilever biosensors that are capable of prompt, real time, cost effective and label free methods of biomolecular recognition have emanated as promising early warning systems for biological defense and have been opted for studies of mass sensing and detection of biological particles. In this sense, the interdisciplinary nature of MEMS could be exploited through merging and synergizing diverse range of fields such as the Lorentz force actuated MEMS magnetic field sensors with the concept of BioMEMS microcantilever sensors by exploring the best of both worlds for achieving the ultimate objective of bioparticle sensing. In the literature, few studies were undertaken that considered the Lorentz force actuation mechanism with the microcantilever based biosensors for detecting the absorption of biological particles on the functionalized region of the sensor. The concentrations of these studies were found to be more oriented towards the simulation or the experimental demonstration of the subject with mere explorations on the optimization of the process parameters. Hence, in order to fulfill the relevant gap, an investigation has been carried out that aims at the design, simulation and optimization of a MEMS magnetic field sensor consisting of a microcantilever with a bioplate as a transducer that is actuated by exploiting the principle of Lorentz force in the static mode. In this study, the system was viewed as a whole and the design and process parameters that were potentially influential on the Lorentz force actuation mechanism of the proposed MEMS magnetic field sensor were identified and classified into categories of variables related to permanent magnet and the microcantilever biosensor. The parameters in the class of permanent magnet were identified as the type, grade, shape and dimensions of magnet and the positioning of the magnet with respect to the microcantilever biosensor in x, y, and z axes. The input parameters with regard to the microcantilever were distinguished as the sizes, materials and shapes of the microcantilever, the conductive path and the biosensor and the amount of current that could be injected into the ports of the sensor. A vacuum region encapsulating the magnetic field sensor and the permanent magnet was defined for the relative packaging of the device. A design of experiments process was modeled for simulating the Lorentz forces in Ansoft Maxwell® FEA software and an optimization procedure was developed that followed a pattern of fixating some parameters and changing only one parameter at a time to determine the relative effect of the considered parameter on the Lorentz force. The case of the varied parameter that yielded the maximum Lorentz force was opted as the ideal case and the subsequent parameter was investigated in the same manner, repeating until a full set of optimized parameters was obtained. The parameters to be optimized were selected as the shape and the ideal dimensional ratios for the magnet, the x, y and z position of the magnet with respect to the microcantilever and the variation of dc current supply. The dimensions, shapes and materials of the microcantilever, the bio-plate and the conductive path remained untouched throughout the optimization process. In addition to this, the optimization of the dimensions of the vacuum box was not conducted due to the automatic adjustment of the vacuum region with a percent ratio relative to the microcantilever and the permanent magnet. Following the series of optimizations, the resulting Lorentz force was concluded to be 2.65 times higher than that of the initial value. A joule heating analysis was conducted in COMSOL Multiphysics® to explore the volumetric distribution of the heat throughout the magnetic field sensors due to the injection of current in the interval of 0-50 mA. The relationship between the current and the average surface temperature on the sensor due to joule heating was plotted from the simulation results so as to find the potential need to define a safe current margin such that the sensor does not begin misfunctioning due to increased temperature. An exponentially increasing relationship was discovered for every incremental rise in the current and hence the 0-15 mA interval was defined to be the safe current range for the respective sensor. The analogy between the Lorentz force and the mechanical deflection of the magnetic field sensor has also been simulated in structural mechanics module of COMSOL Multiphysics® and a linearly increasing trend has been identified from the relationship. After a thorough examination and construction of relationships of the input parameters with respect to the Lorentz force, including the joule heating and the deflectional analysis, the optimized parameter values obtained from the results were employed for modeling five new designs of the microcantilever based biosensor for deriving further evaluations on the developed Lorentz force. A new optimization procedure was prepared in this respect and the effects of increasing the lengths and the widths of the middle arms of conductive paths on the Lorentz force were examined. The acts of lengthening and widening were found to be hardly affecting the Lorentz force but subsequent undertaking of a joule heating analysis for the increased width of the conductive paths presented improved average surface temperature results for the sensor. The thickness of the conductive paths for the current were also varied between 1 µm, 3 µm and 5 µm that yielded no changes on the Lorentz force in Ansoft Maxwell® while worsening the heat distributions on the microcantilever in COMSOL Multiphysics® Houle heating Analysis, thus downsizing the range of safe current. Also, the implication of increasing the surface area of the microcantilever structure with respect to the joule heating was examined and an indirect proportionality was concluded where the expansion in the surface area led to better dissemination of the heat across the volume of the sensor, maximizing the safe current intervals that would result in higher Lorentz force. A fabrication procedure for the MEMS magnetic field sensor was also described comprehensively for its practical realization. A contact has been established with a local permanent magnet manufacturer to see if the optimized dimensional sizes for the NdFe35 type block magnet was commercially available in case that the study is practically implemented. As a proof of concept, the biological warfare agents such as E. coli, variola virus, Influenza A, B and C viruses were modeled and their respective estimative weights were numerically calculated based on the data found on the literature. The translation of the weights induced by these bioparticles on the functionalized gold site of the microcantilever were simulated and the relevant characteristics of the deflections for differing numbers of the respective particles were established for the sensor. Afterwards, the methodology for mass sensing of the bioparticles by the Lorentz force based magnetic field sensor was presented and elaborated by exemplifying with an optical interferometry. The plot of the results of the simulations for the current supply corresponding to the detection of respective numbers of E. coli bacteria illustrated that the current was in the microampere range. Therefore, a requirement for an instrumentation that feeds dc current at microampere range was pointed in order to realize the detection of the respective biological agents by the sensor. Additionally, the bulkiness and the cost of the optical transduction method encouraged discussions relating to the piezoresistive method of detection through a potential modification of the developed sensor such that a compact, ready to use Lorentz force actuated microcantilever biosensor could be employed for practical field implementations in detecting biological warfare agents.
Development of graphene/bismuth nanocomposite film modified graphite electrode for voltammetric determination of heavy metals
In recent years, due to its unique chemical, physical and mechanical features, nanomaterials which are of great interest in many fields such as chemistry, physics, material science are also frequently used for the development of electrochemical nanosensors. By choosing electrodes that are modified with nanomaterials to increase their selectivity and sensitivity, successful results have been achieved in the analysis of analytes at very low concentrations. Graphene, which is a carbon-based nanomaterial and has led to the development of revolution in technology with its discovery, is at the head of the materials used for this purpose. The main difficulty with using the graphene in electrode modification is the synthesis step. According to the method used, conventional methods have drawbacks such as high cost, long synthesis time, the usage of toxic chemicals and small-scale production, so there is a need for a rapid, environmentally friendly, low-cost synthesis method for producing graphene. In the context of this thesis, development of a low-cost, green, sensitive and selective graphene-modified electrode is aimed in order to provide precise simultaneous analysis of heavy metals in water samples. As the first step of electrode development, the surface of the pencil graphite electrode was covered with graphene in one step using an electrochemical method presented in the literature. Cyclic voltammetry (CV) method has been chosen for the modification. In this method, with the application of high anodic potentials to graphite electrode, oxygen-rich graphene oxide was formed, then by applying the potential in the opposite direction oxygen groups were eliminated and graphene structures were obtained. Various modification parameters such as modification electrolyte type and concentration, number of CV cycles, CV scan rate and CV potential range are optimized in order to get the highest response for lead and cadmium. As the second step after electrode development, an electroanalytical method, square wave stripping voltammetry method, was proposed to analyze trace levels of Cd and Pb heavy metals. In this context, the electrode surface was coated with bismuth film in order to increase electrode stability and to obtain higher signals in Cd and Pb analysis. Afterward, parameters including bismuth concentration, deposition potential, deposition time, stirring speed were also optimized. In the end, a certified reference material analysis was conducted for the evaluation of the accuracy of the electrode and method. Successful results were obtained for the Cd and Pb analysis in a working range of 5-100 μg L-1 with the developed electrode. Having a low-cost, environmentally-friendly, rapid, one-step synthesis process, the developed electrode can be used for sensitive and selective trace analysis of various heavy metals in environmental and biological samples.
Elektro-üretim yöntemi ile poliakrilonitril nano liflerden iplik üretilmesi
Nanotechnology is an interdisciplinary technology that finds more application areas to itself over time. Nanoscale materials exhibit different optical, thermal and magnetic properties compared to their bulk forms, and they promise a great opportunity and possibility in technologies including medicine, information technologies, energy and environment. Nano structures are defined as materials with at least one dimension is below 100 nm. However, nanofibers are defined as fibers with diameters less than 1 µm as the current production techniques cannot produce fibers under 100 nm. There are many methods to produce nanofibers. Electrospinning is accepted as the most effective and versatile technology among those methods. Electrospinning process relies on applying electrostatic forces to produce nanofibers from various polymer solutions or melts. Basic set-up consists of three main units; feeding unit (spinneret), collector and high voltage power supply. Voltage is applied to the droplet, which is held at tip of the spinneret`s needle under influence of surface tension. When the electrostatic forces overcome the surface tension, jets eject from the droplet towards to the collector. Jets undergo stretching, elongation, solidification during their travel and nanofibers are collected on the collector. However, they are generally in randomly oriented nonwoven mat form, which limits the utilization areas. In this study it is aimed to modify the needle electrospinning technique in order to obtain three dimensional yarns from nanofibers and expand the usage areas. Polyacrylonitrile (PAN) is a polymer used in many studies due to its suitability for versatile investigations and being precursor of carbon fibers. In this study, PAN is used as the polymer and dimethylformamide (DMF) is used as solvent. Polymer solutions were prepared in three different concentrations. In the first part of the study, experiments and device modifications made based on needle electrospinning technique are explained. In the first studies, three spinnerets, which are connected to positive high voltage power supply, a grounded vertically rotating collector and yarn winding unit was used. It was observed that, although it was possible to obtain staple yarn continuously with that apparatus, all the nanofibers cannot be drawn as yarn due to tendency of the same loaded nanofibers to repel each other. Some of the nanofibers were accumulated on the collector`s walls, which would cause the yarn to break after a while. At this stage the feeding unit has been modified to use two spinnerets connected to positive and negative high voltage power supplies separately, taking advantage of the tendency of oppositely charged nanofibers to hold together. The modified apparatus was finalized using a vertically rotating unearthed collector and yarn winding unit. Ejected nanofibers were deposited towards the collector and formed a nanofibrous web by covering mouth of the collector. A conventional guide yarn, of which one end was attached to collector and the other end to the winding system, was used to pull fibrous web from the center. A cone shape was formed due to pulling of the fibrous web. Vertically rotating collector was used to give twist to the yarn at the apex of the cone. Experiments were done with different polymer concentrations, applied voltage values, polymer feed rates, spinning distances, spinnerets angles, collector types and the speeds of the collector and the winding systems. It was tried to obtain twisted PAN staple yarn, composed of nanofibers, continuously by optimizing all process parameters. It is important to ensure dried nanofibers to join yarn structure as wet nanofibers cause yarn structure to be defected. For this reason, optimization of process parameters has been studied to obtain enough stretching, elongation and solvent evaporation of nanofibers during their travel between the spinneret and the collector. The characterization of the yarns was done visually with scanning electron microscope (SEM). The effects of varying process parameters on nanofiber diameter, yarn smoothness and continuity of the process have been investigated. In the last part of the study, the experimental work held with other spinnable polymers was explained. It was observed that the developed apparatus can be used to obtain yarns from all spinnable polymers.
Optimization of solution blown PVDF nanofibers for air filtration applications
Air purification has become an important issue worldwide as a result of the increasing population and industrial development. Melt-blown filters, spunbond filters, and glass fiber filters are the conventional air filters. Nanofibrous filters, as another and novel alternative for air filtration, offer higher efficiency, lower resistance or pressure drop, longer filter life, and flexibility compared to traditional filters. Mainly, fiber diameter and packing density (solidity) are the dominant factors on the nanofibers for the air filtration performance. This can be explained by the fact that filter efficiency increases when the diameter of fibers decreases. In this study, PVDF based nanofibrous webs were produced for particulate air filtration application. PVDF has extremely good mechanical, thermal and physical properties to adapt to various application areas such as air filters, membranes, supercapacitors, batteries, special textile products in industrial scale application. Its hydrophobic properties make it a perfect material for protective clothes application. In literature, there are lots of publications about PVDF nanofibers and their excellent properties in different application areas. Most of these studies are used electrospinning method to produce PVDF nanofibers. Electrospinning is the well-known method to produce polymeric nanofibers with old history. Unfortunately, due to its low production rate and electric potential, electrospinning method has not been adopted by the industry completely. Centrifugal spinning and solution blown spinning methods are more suitable to produce nanofibers in the industry due to their high production rate and safer components. In non-electro nanofiber production methods, solution blowing is one of the promising technique. Pneumatic forces are used to form the fiber from a polymer solution. In this technique, compressed air forwards the polymer solution towards a collector and fibers are collected as a nonwoven structure on the collector. In this thesis study, PVDF nanofibers are produced by using a semi-industrial solution blowing machine, which has 70 cm width and infinite length. It also has a multi-nozzle system with eight needles, and a hot air system to heat the compressed air to improve the evaporation of solvents. The aim of the study is the optimization of PVDF nanofibers production and to adopt the production of nanofiber webs into the industry for air filters. Firstly to prepare the solutions, DMSO was chosen as the main solvent since it is partially a less hazardous solvent. As a result of this study, homogenous fiber production could not be performed due to the fact that the solvent could not be completely evaporated, so the second set of experiments was conducted with commonly used solvent DMF to produce PVDF nanofibers. To form the design of the experiment, Taguchi method was used and in accordance with the results, optimum conditions were determined. The effect of parameters over the fiber diameter was analyzed. Furthermore, the analysis of variance (ANOVA) was applied to observe the effects of each parameter on fiber diameter. The results were found to be statistically significant. The concentration of polymer solution was determined the most dominant parameter with making contribution approximately 66,75% over the fiber diameter increment. Under optimum conditions, nanofibrous webs were produced and subsequently the air filtration efficiency of the webs was tested. The filtration properties of the nanofibrous webs comprised of several samples that have different average fiber diameters, which involves the optimum sample, were analyzed. With the optimum sample was obtained the maximum filtration efficiency, Knudsen number, and quality factor values. The results showed that the average fiber diameter was dominant over the air filtration performance. The results also showed that the filtration efficiency of the optimum sample had approximately EPA 11 level efficiency. After the filtration results, solution blow spinning with higher fiber production efficiency can be concluded as a feasible method of producing high-performance air filters.
Interaction of Poly(vinyl alcohol) and chitosan coated iron oxide nanoparticles with cell membrane models
Nanotechnology is being used at different fields from energy to food industry but its application to medical field, such as tissue engineering, bioimaging, drug design, diagnosis, is more recent. According to the World Health Organization (WHO), 8.8 million people were reported dead because of the cancer in 2015. Cancer can be treated with chemotherapy, radiotherapy and surgery but these treatment methods have serious side effects since cancer drugs are not selective so they affect both healthy and cancerous cells. One of the approaches to reduce the toxic side effects and improve patient life quality is the implementation of nanotechnology to the development of new drugs and therapies. Magnetic nanoparticles are usually made up of nickel, cobalt and iron. Because of their magnetic properties, they can be transferred to desired location with the help of external magnetic field. Generally, magnetite, hematite, maghemite and goethite are known as iron oxides types. Iron oxide nanoparticles (IOPs) are commonly preferred as MRI agent, and targeted drug design. They are, however, toxic and cause problem in physiological environment because of their negative surface charge, easy agglomeration, low stability, and free radical formation. Therefore, they should be modified to reduce their toxicity and coating their surface with polymers is an effective method proposed by different groups. In this study, iron oxide nanoparticles were coated with two different polymers and the interaction of these particles with cells were studied using artificial cell membrane models. For this purpose, chitosan and poly(vinyl alcohol) (PVA) were selected because of their biodegradable and biocompatible characteristics. Polymers were coated on IOPs surfaces by adsorption method because of its high efficiency and simplicity. In this method, polymer solutions at different concentrations were mixed with IOPs. Optimal polymer concentration was determined according to colloidal stability. Characterizations of the IOPs were done using different techniques. Zeta potential was measured to determine the surface charges, and stability, rheology to observe flow behavior, Dynamic Light Scattering (DLS) to measure particle size, and Fourier Transform Infrared Spectroscopy (FTIR) to investigate binding between IOPs and polymers. After the characterization, interaction between cell and coated and uncoated IOPs were investigated with liposome, a simple biomimetic cell membrane model. Quartz Crystal Microbalance with Dissipation (QCM-D) is used to investigate these interactions in real time and label-free. QCM-D uses piezoelectric effect of quartz crystal. When voltage is applied, quartz crystal oscillates with a defined frequency and this frequency is sensitive to the amount of material attached to the surface. Adsorption/desorption or solid/liquid interaction can be observed according to the frequency shift (Δf). QCM-D also measures viscoelastic properties of adsorbed particles on surface with changes of dissipation (ΔD) at the same time. In this thesis, the interaction of PVA and chitosan fully coated, partially coated, and uncoated IOPs were investigated with neutral, positive and negatively charged liposome layers. By using QCM-D, interactions of particles with cell were estimated in a shorter time and cheaper than cell culture experiments. Results show that, coating properties, structure and charge of lipids affect the interactions between them and electrostatic interactions are significant parameter. In the future studies, chemotherapeutic drug loaded particles can be studied both in QCM-D and cell culture to see their effect to the cells.
Investigation on the effects of mechanical forces on endothelial and monocytic cell behaviour by using microfluidic systems
In human physiology, it is known that cells can sense not only biochemical signals but also physical factors which employee in tissue functionality such as mechanical forces, geometry and matrix flexibility. Mechanobiology is the field of these physical factors function basically through mechanotransduction process. The mechanotransduction is a physiological process that is needed to sense mechanical forces and the conversion of these forces into electrical and biochemical signals. For instance, tensile strength, compression and shear stress, are the most important mechanical stimulations which have influence on cells in body. These mechanical stimulators playing major role on regulation of cellular functions like gene expression, protein synthesis, cell growth, differentiation and death which are necessary for providing the maintenance of tissue balance by triggering different electrophysiological and biochemical responses. Traction forces formed by sensing extracellular environment and responses to this environment can affect many biological processes like wound healing, angiogenesis and metastasis at cell level. Therefore, characterization of these mechanical forces in terms of magnitude and direction could be meaningful in pretending and understanding the physiological and pathological events at tissue and organ level. In tissue and organ level, shear stress which is described as the friction force per unit area in blood has tremendous importance in terms of evolution and physiology over the endothelial cells covering the inner surface of vascular network to maintain the physiological conditions. This shear stress is related to flow rate gradient on the cross section of a tube. While velocity is maximum at center, it is zero near to the inner surface. It is known that the biological responses to shear stress takes a significant part of preventing vascular diseases. Due to non-pulsatile characteristic of venous system, shear stress levels are low and between 0.076-0.76 Pa. In arterial system, flow is laminar and pulsatile with high shear stress levels that are between 1-7 Pa for large arteries and between 2-6 Pa for arterioles. Studying vascular cell biology in laboratory is difficult in terms of mimicking the dynamics in vivo environment and 3D structures. Work done by in vitro is achieved by exposing the endothelial cells into shear force in flow chambers composed of parallel plates. Besides, thanks to the devices produced by microfluidic technology which can be used instead of huge systems such as parallel plate or cone plate flow chambers, the mechanical forces, especially shear stress can be studied in in vitro environment. Because of being cheap, biocompatible and transparent, poly(dimethylsiloxane) is used in production of microfluidic devices which is used usually in cell biology studies. There are some advantages of microfluidic devices produced by poly(dimethylsiloxane) like using small amount of sample or agents, providing cell culture environment with stable liquid flow compared to traditional methods used in cell culture applications and analysis. Also, microfluidic devices are made of transparent materials, have suitability to fluorescence microscope or spectroscopy studies which enable monitoring cell behavior under long-term and high amplification conditions. In this thesis, the microchannels were designed as cavitated to mimic the environment of the atherosclerotic plaque where the shear stress and pressure difference occur depending on the diameter of the vessels and fabricated using MEMS techniques.. HUVEC is endothelial cells which is lining the inner surface of the wall seeded in the straight and cavitated microchannels were subjected to shear stress at 0.25 and 0.75 Pa, separately, for 4 hours by the syringe pump. Also, there are two subgroups as TNF--treated and untreated. The change of F-actin level in HUVEC was investigated under fluorescence microscope and fluorescence intensity of F-actin protein level was examined by Image J 1.50i programme. According to the results, there is a significant increase at 0.25 Pa in straight microchannel group with respect to control counterpart for untreated group. There is a significant decrease at 0.75 Pa groups compared to 0.25 Pa groups but MFI increased only in 0.25 Pa straight microchannel compared to control. Overall, the MFI of F-actin at 0.25 Pa is significantly higher than 0.75 Pa for TNF--untreated group. In TNF--treated group, there is not any significant difference between experimental groups. The change of ICAM-1 mRNA levels in HUVEC cells was investigated by qRT-PCR. For untreated group, there is significant increase at 0.25 Pa in cavitated group. The mRNA expression level at straight groups are lower than cavitated groups. For TNF--treated group, the mRNA expression level at 0.25 Pa is higher than 0.75 Pa for cavitated group. There is a significant difference between straight and cavitated groups at 0.25 Pa. The mRNA expression level at 0.25 Pa cavitated group is higher than control. F-actin synthesis and ICAM-1 mRNA levels have also been investigated in monocyte cells as examined in endothelial cells due to the contribution of monocytes to the process of inflammation in atherosclerotic plaque regions. In this direction, THP-1 cells were exposed to 4, 15 and 45 Pa shear stress, for 0.5 and 3 hours, separately. In addition, since TNF- is known to enhance the synthesis of F-actin polymer and ICAM-1 gene expression, experimental groups were divided into two subgroups, treated and not treated with TNF-. F-actin synthesis in Phalloidin labeled THP-1 cells was examined by fluorescence microscopy and fluorescence intensity was analyzed by Image J 1.50i program. According to the mean fluorescence intensity, F-actin synthesis was observed significantly increased at 4 Pa and 45 Pa shear stresses after 0.5 h, while the greatest increase was observed at 15 Pa. As the duration of exposure increased, a decrease in F-actin polymerization was observed at 45 Pa. Since the increase in F-actin synthesis was seen at a maximum 15 Pa shear stress, the determination of ICAM-1 mRNA level in THP-1 cells was only examined by qRT-PCR at 15 Pa. According to the results, about two-fold increase was observed in the experimental group compared to the control group. The releasing level of IL-8 chemokine molecule from THP-1 cells exposed to shear stress which secreted for leukocyte recruitment from monocyte and endothelial cells in atherosclerotic regions was examined. For this reason, the level of IL-8 in THP-1 cells were exposed 4, 15 and 45 Pa shear stress for 3 hours was examined by ELISA. According to the fluorescence intensity results, a decrease in the experimental groups was observed compared to the control group. Except the control group, the highest level was observed at 15 Pa and the lowest level at 45 Pa. Hoescht 33342 fluorescently labeled THP-1 cells were exposed to 15 Pa shear stress for 0.5 and 3 hours, respectively, were added to the HUVEC cells seeded in the wells and incubated for 1 hour, the florescence images were taken after incubation to investigate how the shear stresses affected the adhesion between the endothelial and monocyte cells. The number of cells adhered to HUVEC cells was analysed with Image J 1.50i programme. According to the results, as the duration of exposure to shear stress increases, the degree of adhesion decreases. Data obtained from these experiments will enable diagnostic, treatment and new medicine designs by revealing the targeted molecular mechanism definitely in atherosclerosis treatment within the scientific area by the future. Furthermore, examination of the changes in the molecules involved in sheared cells by microfluidic systems will greatly contribute to the work to be done in the field of nanotechnology.
Biomimetic approaches for the fabrication of hollow fiber nanofiltration membranes
Membrane technologies have become pioneer technology for the water treatment. However, the operation cost of the membrane is dependent on fouling which is "the Achilles heel of the membranes" and consumed energy. The high energy requirements in commercial nanofiltration (NF), reverse osmosis (RO) and forward osmosis (FO) technologies lead researchers to develop new membrane designs having high flux values with high salt rejection values. Biomimetic approaches have gained an important place in the scientific and the technical fields. For the research and development of the membranes, the terms "learning from nature" and "innovation by imitating" become significant. In this respect, Aquaporin Z (AqpZ) protein became popular for the last eleven years. These membranes promise extremely high performance enhancements and offer a decrease in energy consumption. This thesis aims to conduct a very comprehensive study on the development of hollow fiber nanofiltration membranes with incorporated AqpZ. For this purpose, AqpZ protein was cloned from E.Coli bacteria by using many molecular methods such as PCR, ligation, chemical transformation etc. After AqpZ gene is confirmed by sequencing, purification of AqpZ is optimized. Functionality of AqpZ is obtained by reconstituting AqpZ into liposomes. Film rehydration method is used for liposome preparation. In the thesis, the effect of Aquaporin Z (AqpZ) reconstitution on liposome characteristics and behaviors was investigated by evaluating the adsorption performance of proteoliposomes onto gold, polysulfone (PS) and polyacrylonitrile (PAN) surfaces. Commercial AqpZ were used as positive control for cloned AqpZ. AqpZ incorporation into liposomes did not significantly change mean liposome diameter and surface charge, but the water permeability was increased up to almost six fold. Adsorption kinetics was monitored on gold, as the reference substrate, on PS and on PAN spin-coated sensor surfaces, as common nanofiltration membrane materials, via Quartz Crystal Microbalance with dissipation (QCM-D). The results of viscoelastic modelling showed stiffer membrane structure for the lipid bilayer of proteoliposomes compared to that of liposomes. Although liposomes and proteoliposomes were found to be successfully adsorbed on negatively charged PS and neutral charged PAN surfaces, the interaction strength and adsorption rate was found to be different for polymers having different surface properties indicating the importance of polymer for the stabilization of proteoliposomes. According to the findings of this study, PS was chosen as polymer material for membrane fabrication. Interfacial polymerization method was used to fabricate hollow fiber nanofiltration membranes. Proteoliposomes were added to the aqueous phase of interfacial polymerization. Proteoliposome concentration and interfacial polymerization conditions were optimized with flat sheet membranes. Two different proteoliposome concentrations, two different amine monomer reaction times were used and the effects of thermal treatment was investigated for the optimization of flat sheet membranes. Membrane performances were compared in terms of specific permeate flux, MgSO4 and humic rejection; flux recovery after humic acid filtration, the performance of cloned AqpZ incorporated membranes improved 1.7 times regarding TFC membranes. According to the results, increasing liposome concentration did not improved nanofiltration membrane performance. On the contrary, salt rejection performance decreased dramatically. 0.1 mg/mL proteoliposome concentration, 2 min piperazine monomer reaction time and thermal treatment at 50°C for 5 min was found to be the optimized condition. Hollow fiber ultrafiltration membranes were fabricated by phase inversion method. Ultrafiltration (UF) membrane morphology and performance was confirmed by characterization methods. UF membranes were used as support layer for nanofiltration membrane fabrication. For this purposes, in the thesis the combined effects of fabrication conditions and casting mixture composition on the properties of hollow fiber (HF) membranes were investigated. Three variables evaluated are air gap (dgap= 0 cm and 2.5 cm); coagulation bath temperature (Tc= 25°C; 35°C; 45°C) and molecular weight of polyvinylpyrrolidone (MWPVP = 10 kDa; 40 kDa; 65 kDa; 360 kDa; 1000 kDa). Prepared HF membranes were characterized in terms of specific permeate flux; surface morphology, charge and hydrophilicity; bovine serum albumin (BSA) rejection, Young modulus, and resistance to fouling by BSA. Optimal membrane morphology and performance was achieved at higher Tc and higher MWPVP. Optimized conditions were used for the preparation of hollow fiber nanofiltration membranes with Aquaporin Z (AqpZ) immobilized on the outer surface of the separation layer. Three ultrafiltration supports – polymeric, nanocomposite and reinforced were evaluated in terms of their effects on the separation properties of membranes with AqpZ. Surface characterization showed that AqpZ-reconstituted proteoliposomes were successfully integrated with the polyamide matrix leading to permeate flux enhancement of up to 2.5 times. The membranes were also evaluated in terms of salt and organic matter removal. Reinforced UF support allowed for the most effective integration between the polyamide layer and proteoliposomes giving the highest figure of merit – an aggregate metric of membrane performance that includes water permeability, selectivity and resistance to fouling.
Persea americana Mill. yapraklarından sentezlenen gümüş ve altın nanopartiküllerin biyolojik aktivitelerinin değerlendirilmesi
Nanoteknolojinin bilim ve teknoloji içerisinde multidisipliner bir alan olması sayesinde özellikle nanopartiküllerin üretimi ve kullanımı son zamanlarda yaygınlaşmaktadır. Ayrıca, dünyadaki değişimin bir sonucu olarak inovatif ve ekolojik olarak çevre dostu bilimsel yöntemlerin geliştirilmesine olan ilgi de artmaktadır. Bu tez çalışmasının amacı, Persea americana Mill. (Avokado) yaprak ekstraktları aracılığıyla gümüş ve altın nanopartikül sentezi gerçekleştirmek ve sentezlenen gümüş ve altın nanopartiküllerin biyolojik aktivitesini incelemektir. Persea americana Mill., endüstriyel tarıma ihtiyaç duymadan doğal olarak yetişebilen ve aynı zamanda Akdeniz bölgesinde de kültürü yapılabilen bir bitkidir. Ayrıca içerdiği temel besinler ile hem meyveleri hem de yaprakları ile farmakolojik, kozmetik, diyetetik açıdan önemli bir yer tutmaktadır. Bundan hareketle yapılmış olan bu tez çalışmasında Persea americana Mill. (Avokado) yapraklarından su ekstraktı hazırlanmış, daha sonra yeşil sentez yaklaşımı ile gümüş ve altın nanopartikül sentezi gerçekleştirilmiştir. Elde edilen sonuçlara göre gümüş nanopartikül sentezi sonucunda sarıdan kahverengiye dönen çözelti rengi oluşmuş, altın nanopartiküllerde de altın sarısı renginden kırmızımsı renge dönüşen çözelti rengi gözlemlenmiştir. Nanopartikülleri yapısal ve morfolojik açıdan incelemek amacıyla ultra-viyole (UV-Vis) spektroskopisi, Fourier dönüşümlü kızılötesi spektroskopisi (FT-IR), taramalı geçirimli elektron mikroskopisi (STEM), X-ray difraktometresi (XRD), nanopartikül boyut ve Zeta potansiyeli ölçümü gibi çeşitli yöntemlerden yararlanılmıştır. Karakterizasyon bulgularına bakıldığında gümüş nanopartiküller genellikle küresel şekle sahip olan ve ortalama 12.18 ± 2.18 nm aralığında görülmekte iken altın nanopartiküllerin de küresel ve üçgen şekilli morfolojiye sahip ve ortalama 14.84 ± 3.99 nm boyutlarında olduğu tespit edilmiştir. Avokado yaprak ekstraktı ve yaprak ekstraktından sentezlenen gümüş ve altın nanopartiküllerin toplam fenolik ve toplam flavonoid madde tayininin yanı sıra toplam antioksidan kapasite (fosfomolibdat), DPPH, ABTS, CUPRAC, FRAP ve metal şelatlama gibi çeşitli metotlar kullanılarak antioksidan aktivite testleri gerçekleştirilmiştir. Yapılan antioksidan testlerinde gümüş nanopartiküllerin Fosfomolibdat aktivitesi 0.29 mmol TE/g, DPPH aktivitesi 20.94 mg TE/g, ABTS aktivitesi 25.66 mg TE/g, CUPRAC aktivitesi 61.39 mg TE/g, FRAP aktivitesi 41.99 mg TE/g olarak tespit edilmişken altın nanopartiküllerin ise Fosfomolibdat aktivitesi 0.05 mmol TE/g, DPPH aktivitesi 28.14 mg TE/g, ABTS aktivitesi 1.40 mg TE/g, CUPRAC aktivitesi 35.50 mg TE/g, FRAP aktivitesi 21.48 mg TE/g olarak belirlenmiştir. Elde edilen sonuçlar avokado yaprak ekstraktının ve ekstrakttan sentezlenen gümüş ve altın nanopartiküllerin antioksidan etkiye sahip olduğunu göstermiştir.
Yumuşak jelatin kapsül ile kanabidiol içeren kenevir tohumu yağı uygulaması için polikaprolakton modifiye salım sistemi geliştirilmesi
Kanabidiol (CBD); multiple skleroz, parkinson, anoreksiya, göz tansiyonu, kanser, ağrı, bulantı ve kusma, depresyon, insomnia, stres ve kaygı bozuklukları gibi çeşitli hastalıkların tedavisinde umut vadetmektedir. Fakat CBD'nin yüksek lipofilik özellikleri, kullanım ve dozlamayı zorlaştırmakta, dolayısıyla farmasötik olarak yararlanımını kısıtlamaktadır. Bu tez çalışmasının amacı, CBD'nin gıda takviyelerinde kullanılması için elverişli bir dozaj formu geliştirilmesi ve başarılı bir şekilde kapsüllenmesinin sağlanmasıdır. Nanopartiküller (NP), farklı molekül ağırlıklarına sahip polikaprolakton (PCL) polimerleri kullanılarak, ultrasonik homojenleştirici ve ultra-turrax ile emülsifikasyon çözücü buharlaştırma yöntemi ile sentezlenmiştir. Optimizasyon çalışmalarında, farklı molekül ağırlıklarının ve farklı üretim yöntemlerinin partikül boyutuna ve zeta potansiyeline etkileri değerlendirilmiştir. En uygun polimerin 14000 g/mol molekül ağırlığına sahip PCL olduğu bulunmuş ve 5 mg, 10 mg, 15 mg ve 30 mg CBD enkapsüle edilmiş PCL NP'ler ultrasonikasyon tekniği kullanılarak hazırlanmıştır. CBD enkapsüle NP'ler morfolojik ve yüzey özellikleri açısından karakterize edilmiştir. Plasebo NP'ler ve 5mg, 10 mg, 15 mg ve 30 mg CBD enkapsüle PCL NP için sırasıyla -23,37, -10,21, -9,62, -9,93 ve -9,40 mV'lik potansiyel değerleri tayin edilmiştir. Plasebo NP'ler ve 5 mg, 10 mg, 15 mg ve 30 mg CBD enkapsüle PCL NP'lerin sırasıyla ortalama 207,5 nm 227,2 nm, 225,5 nm, 227,7 nm ve 216,9 nm boyuta sahip oldukları belirlenmiştir. İki farklı pH değerinde (1,2 ve 7,4) CBD-PCL-NP'lerin in vitro salım çalışmaları gerçekleştirilmiştir. NP'lerin DSC analizi ile etken madde-polimer uyumluluğu ortaya çıkartılmıştır. Ayrıca FT-IR analizi sonuçlarıyla, CBD'nin NP'ler içine kapsüllendiği gösterilmiştir. CBD'nin çeşitli reseptörlerle etkileşiminin incelenmesi için moleküler yerleştirme yöntemi kullanılarak in silico analizleri yapılmıştır. Bu molekülün reseptörler üzerinde yapısal davranışları, afinitesi ve toksisitesi değerlendirilmiştir. PCL-NP'nin hücre içerisine alındığı ise Nil kırmızısı enkapsüle edilmiş NPlerin hücrelerin içerisinde birikimi gösterilerek ortaya koyulmuştır. Saf CBD'nin hücrelerin çoğalmaları üzerindeki etkisi ise L929 normal fibroblast hücreleri ve MCF-7 meme kanseri hücrelerinde 24, 48, 72 saat inkübasyon sonrası hücre canlılık analizi yapılarak ve IC50 değerleri hesaplanarak belirlenmiştir. Sonuçlar, CBD-PCL-NP'lerinin kenevir tohumu yağıyla birlikte, yumuşak jelatin kapsül formunda bir gıda takviyesi olarak geliştirilebileceğini göstermiştir. Gıda takviyesi uygulaması için kullanılmak üzere elde edilen kenevir tohumu yağının yumuşak jelatin kapsül formunda prototip üretimi gerçekleştirilerek ambalajlanmıştır. Kapsülün, uzun süreli CBD salımı yaparak serbest CBD tüketimine göre farmasötik avantajlara sahip olduğu söylenebilir.
Oksijen ve sıcaklığın reaktif magnetik alan sıçratma yöntemiyle büyütülen çinko oksit ince filmlere etkisi
Çinko oksit (ZnO), yarı iletken endüstrisinde gösterdiği saydam iletken oksit (SİO) özelliği ile hızla gelişmekte olan optoelektronik teknolojisinde sıklıkla kullanılan bir malzemedir. Bu tez çalışmasında, reaktif radyo frekans magnetik alan sıçratma yöntemi ile büyütülen ZnO ince filmlerin büyütme esnasında ortamda bulunan oksijen ve alttaş sıcaklığına bağlılığı yapısal ve optik özellikleri açısından değerlendirilmiştir. Yapılan X-ışınları kırınım deseni analizleri sonucunda elde edilen bulgular incelendiğinde bütün filmlerin yüksek yönelime sahip hekzagonal wurtzite yapısında olduğu ve bunun O2 miktarına bağlı olmadığı sonucuna ulaşılmıştır. Ayrıca, Raman spektrumları da wurtzite yapısının varlığını doğrulamaktadır. Aynı zamanda tüm örneklerin yüksek geçirgenliğe sahip olduğu ve film kalınlıklarının sıcaklık artışı ile azaldığı tespit edilmiştir. Alan etkili taramalı elektron mikroskobu (FE-SEM) ve atomik kuvvet mikroskobu (AFM) sonuçları ise filmlerdeki taneciklerin oda sıcaklığında, 100 oC'de ve 200 oC'de çok değişmediği ancak 300 oC sıcaklıkta büyütülen filmlerin homojen olmayan tanecik büyümesi sergilediği tespit edilmiştir. Ancak, bu durum O2 arttıkça azalmaktadır. Bütün filmler için optik bant boşluğu ⁓3.25 eV olarak tespit edilmiştir. Yapılan bu çalışma, optoelektronikte oldukça sık kullanılan ince film çinko oksit yapılarına ilişkin kapsamlı bir optimizasyon sunmuştur.
Perovskite güneş hücreleri için metal oksit alttaşların üretimi ve tasarımı
Tez çalışmasında, düzlemsel mimariye sahip perovskite güneş hücrelerinde (PGH) kullanılmak üzere optimize edilmiş indiyum kalay oksit (ITO) ve flor katkılı kalay oksit (FTO) alttaşların üretimi, karakterizasyonu ve hücre uygulamaları gerçekleştirilmiştir. Bu çalışmanın amacı, ticari alttaşlara kıyasla daha üstün optoelektronik özellikler sunan metal oksit alttaşları üreterek perovskite hücrelerinin performansını artırmaktır. ITO ve FTO alttaşlar, magnetron saçtırma yöntemi kullanılarak RF ve DC güç kaynaklarıyla farklı güç değerlerinde (optimum değerler sırasıyla 320 W ve 137 W) ve sistem için ideal kabul edilen ~5 x 10⁻³ Torr basınç altında üretilmiştir. Düşük basınçta plazma yoğunluğundaki kararsızlık nedeniyle bu strateji tercih edilmiştir. Üretimler, ITO için oda sıcaklığında, FTO için ise 150 °C'de gerçekleştirilmiştir. FTO üretimi sırasında yapıda oluşabilecek oksijen eksiklikleri, ortama az miktarda oksijen verilerek azaltılmaya çalışılmıştır. Üretilen ITO ve FTO kaplı camların elektriksel dirençleri ölçülmüş, ardından farklı sıcaklıklarda tavlama işlemi uygulanmıştır. Karakterizasyon sonuçları, özellikle ITO alttaşların güneş hücreleri için umut verici özellikler sergilediğini göstermiştir. ITO ve FTO alttaşlar, elektrot/c-TiO₂/perovskite/spiro-OMeTAD/Au mimarisine sahip hücrelerde elektrot olarak kullanılmış ve fotovoltaik performansları ticari ITO (Sigma-Aldrich, Kintec) ve FTO (Sigma-Aldrich) alttaşlarla karşılaştırılmıştır. Sonuçlar, proje kapsamında geliştirilen ITO filmlerin ticari ITO'ya göre daha üstün optik ve elektriksel özellikler sergilediğini ve fotovoltaik verim açısından daha yüksek sonuçlar elde edildiğini ortaya koymuştur. Akım yoğunluğu-voltaj (J-V) karakteristiklerine göre, ticari ITO kullanılan en iyi hücrede %19.9 verim elde edilirken, tez çalışması kapsamında geliştirilen ITO kullanılan hücrede %20.2 verime ulaşılmıştır. Sonuç olarak, bu tez, optimize edilmiş ITO alttaşların güneş hücrelerinde verimliliği artırma potansiyeline sahip olduğunu ve gelecekte optoelektronik aygıt teknolojisinde daha geniş uygulama alanı bulabileceğini göstermektedir.
Electrospun PCL/P3ANA nanofibers as electroactive-bioactive biomaterial for bone tissue regeneration: synthesis, characterization and cell studies
An electroactive and bioactive nanofiber scaffold which serves both chemical and physical bioactive signals for cells, was fabricated. Electrospun poly(ε-caprolactone)/poly(m-anthranilic acid) (PCL/P3ANA) nanofibers were fabricated by addition of increasing amounts of P3ANA to the PCL solutions. The addition of P3ANA in higher amount resulted a decrease in fiber diameter and high surface roughness and large surface area. The increased surface area of PCL/P3ANA nanofibers serves more available sites and carboxyl groups for biofunctionalization with growth factors. The mechanical properties of PCL/P3ANA nanofibers changed due to P3ANA amount which changed the structural properties of the nanofibers. Electrochemical impedance spectroscopy (EIS) measurements showed that the increase of P3ANA amount in the PCL/P3ANA nanofibers resulted lower charge transfer resistance values which indicates higher conductivity. Higher electroactivity is advantageous in terms of delivering electrical signals to cells. Therefore the PCL/P3ANA nanofiber scaffold containing the highest amount of P3ANA with highest surface area, best mechanical and electrochamical properties was chosen for biofunctionalization and electrical stimulation of cells. PCL/P3ANA nanofiber scaffold was biofunctionalized with covalent protein attachment by using 1-ethyl-3-(dimethyl-aminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) activation process. The activation process was investigated and it was found that 50/50 mM of EDC/NHS was the most effective concentration for the activation of PCL/P3ANA nanofibers. After determination of the suitable nanofiber mat for cell culture studies and the optimum concentrations of EDC/NHS for covalent immobilization, PCL/P3ANA nanofiber scaffold was biofunctionalized with growth factors of bone morphogenetic protein-2 (BMP-2) and RGD peptide for in vitro cells studies. The amounts of covalently immobilized BMP-2 and RGD peptide were determined by bicinchoninic acid (BCA) protein assay and with elemental analyzes of N atoms by Energy-Dispersive X-ray Spectroscopy (EDX). Contact angle measurements showed the changes of the surface properties from hydrophobic to hydrophilic after protein immobilization. The increase in the double layer capacitance and charge transfer values of nanofibers after protein immobilization was showed with EIS. Nanofibers were nontoxic and enable for attachment and growth of Saos-2 cells. The cell proliferation was the highest for the RGD peptide immobilized nanofibers. Cell viability is in correlation with cellular adhesion and structure of the scaffold. Cell morphology was polygonal in shape on the PCL, PCL/P3ANA and PCL/P3ANA-RGD nanofibers is similar to each other. The cells on BMP-2 functionalized nanofibers exhibited osteocyte-like morphology. Alkaline phosphatase (ALP) activity and calcium deposition of Saos-2 cells cultured on cover glass, PCL, PCL/P3ANA, BMP-2/PCL/P3ANA and PCL/P3ANA-RGD nanofibers were investigated. The cells on BMP-2 immobilized nanofibers had the highest ALP activity and the highest amount of calcium deposits among all nanofibers and cover glass, which indicates a higher degree of osteogenesis. The effects of electrical stimulation on the differentiation of Bone Marrow Mesenchymal Stem Cells (BMSCs) into bone feature and the ability of PCL/P3ANA nanofibers to deliver the electrical signals to the cell were investigated. Electrical stimulation was applied to the cells with the electric field (voltage difference per unit distance) of 200 mV/mm, 400 mV/mm and 800 mV/mm at frequency of 0.5 kHz, 1 kHz, 5 kHz and 10 kHz. The viability of cells was the highest when frequency of 1 kHz was applied. At frequency of 0.5 kHz and 1 kHz, the highest viability was observed when cells stimulated with 400 mV/mm. When 800 mV/mm AC voltage at any frequency was applied, cell viability was below 50%. The higher frequencies (5 kHz and 10 kHz) caused a dramatic decrease in cell viability. The cells cultured on the PCL/P3ANA nanofibers under electrical stimulation, proliferated by spreading on the nanofiber mats. At 200 mV/mm and 400 mV/mm voltages BMSCs showed osteocyte-like morphology with adherent-cell type actin extensions. Osteogenic differentiation of BMSCs was investigated by staining for ALP activity and Ca deposits. ALP activity and Ca deposition data exhibited similar trend to the proliferation results. The cells stimulated with voltage of 800 mV/mm exhibited almost no ALP activity or mineralization. The highest mineralization and ALP activity was observed when BMSCs stimulated with 400 mV/mm at 1 kHz. The electrical stimulation data suggested that P3ANA in the nanofiber structure was capable of delivering, interacting and mediating the electrical signaling process within the seeded BMSCs.
Fabrication and characterization of support layer for thin film nanocomposite desalination membranes
The production of potable water has become a global concern; for many communities, conventional available water resources are inadequate in supplying the demand due to rapid population growth and industrialization. Desalination of brackish or seawater has become an important source of both drinking water production and irrigation. The leading technology is reverse osmosis (RO) membrane process and is accounted for producing more than half of the world's desalination capacity. Significant development in membrane materials and technologies; in terms of module and process design, feed pre-treatment and energy recovery in the past few decades have greatly improved the cost effectiveness and performance capability of membrane processes and have made the RO technology dominating in the desalination market. Owing to showing inherently high salt rejection and durability with small footprint and ease of the operation, polymeric membranes have governed the RO membrane industry. On the other hand, there are several severe problems need to be eliminated such as comparatively low permeability due to their characteristic hyrophobicities, low boron removal and fouling issues. In order to resolve aforementioned problems, different approaches were developed. Among them, thin film composite (TFC) membranes have drawn substantial attention since their invention by Cadotte et al. in the 1970s in which a thin selective polyamide (PA) layer is formed on top of a microporous support by in-situ interfacial polymerization (IP) technique and these membranes have high salt rejection values over 99%. Although, commercially available PA-TFC membranes can remove almost all ions in the seawater, their boron removal values are around 95% under normal test conditions. Recently, a new concept of mixed-matrix composite RO membranes was reported by incorporation of nanoparticles such as carbon nanotubes (CNTs) and zeolites into the thin selective PA barrier in the course of IP process. Both experimental and molecular simulation studies have shown that the use of CNTs in PA layer resulted with enhanced water flux and improved salt rejection values compared with conventional counterparts that are mainly because of their preeminent characteristics, and ease of functionalization with various functional groups. This thesis aims to develop a novel fabrication method of thin film nanocomposite (TFN) membrane for RO technology in which single-walled CNTs are embedded in PA selective layer during IP process on top of a microporous polysulfone (PSf) substrate with the purpose of increasing the boron rejection capacity and improving the water flux as well. Experiments were performed at three stages: i) preparation of porous polysulfone (PSf) substrate by phase inversion method and optimization of the process parameters such as addition of pore-former agents, changing the type of non-solvent and modifying the temperature of precipitation medium, ii) the development of TFC membranes on PSf supports having different pore sizes and optimization of the IP process conditions such as altering the monomer concentrations and reaction time, iii) fabrication of TFN membranes by means of filtration of commercially available –COOH functionalized SWCNTs on PSf support prior to IP process for the semi-alignment of the nanotubes. For the characterization of the resultant membranes field emission scanning electron microscopy (FESEM) and contact angle measurements were employed to investigate both the surface and cross-sectional morphology, and surface hydrophilicity, respectively. Performance evaluations of the fabricated membranes were conducted using a laboratory scale cross-flow membrane test unit. According to the results, the ideal PSf substrate membrane for the incorporation of SWCNT into PA layer was obtained from the recipe of 15 wt.% PSf with the addition of 10 wt.% pore-forming agent which was polyvinylpyrrolidone (PVP) and precipitated in cold isopropyl alcohol. On the other hand, regarding to TFC results; SEM micrographs have shown that pore size of the PSf support has great impact on the resultant PA layer. Relatively smaller pores produced thicker PA layer due to the limited diffusion of aqueous m-phenylenediamine (MPD) solution into the small pore channels, whereas larger pores produced thinner PA layer mainly because of ability of MPD solution to penetrate deep into the pore channels and at the same time these big pores act like a MPD reservoir in which subsequent trimesoyl chloride (TMC) introduction will produce PA layer. Other than characteristics of PSf substrate, the PA layer thickness was affected by the interfacial polymerization reaction time in such a way that longer the polymerization time is applied, the thicker the cross-linked PA layer is formed. The 15 s reaction time produced around 100 nm PA layer, while doubling the reaction time from 15 s to 30 s formed approximately 1 µm-thick PA barrier. In addition to these, the effect of MPD concentration was also studied. Increasing the amount of MPD can caused to form thicker layer than its low concentration counterpart produced. All the results were consistent with the literature. In order to test the fabricated membranes in the testing cell having 140 cm2 test area, various masking techniques with Al tape and foil were tried and finally the most proper method has been developed. This newly developed technique enables to test the performance of the membranes having smaller areas than the test cell. Technique was tested with a membrane having a known specification. Results showed that the developed method works successfully without any leaking. In this regard, one of the fabricated membranes TFC-5 was tested in order to determine the performance of synthesized membranes so that to reflect a representative result. Salt rejection was calculated by measuring conductivity of the solutions before and after, which were feed and permeate, respectively. The rejection value was calculated as ~85% at 2000 ppm NaCl, which was smaller than the commercial membranes. These results have shown that the fabricated membranes can be improved in terms of fabrication technique to obtain better results. Nevertheless, this study contains noteworthy clues with respect to membrane masking and is still a guidance for the fabrication of substrate membranes for high boron rejection TFN membranes that can be used for desalination applications.
Preparation and characterization of anti bacterial, anti scratch and easy to clean multifunctional coatings by sol gel method
Developments of science and technology help us to understand the relationship between microstructure and material properties. Materials gain new properties by decreasing their particle size from micro to nano scale. Nowadays, thin film coatings on solid surface are developing by various physical and chemical coating methods. In order to show functionality, thin coatings must have homogeneous thickness and composition throughout the coating layer. Coating methods are generally divided as physical and chemical coating methods. Among the coating methods, sol-gel method come forward as a chemical method to develop multifunctional coatings. In general, sol gel is defined as the transition from a liquid sol phase to solid gel phase. Sol-gel process does not require high process temperatures and in this process, there is a control of the material from precursor to final product at molecular level. It is a low cost process, capable to coat flat or geometric shapes and large areas as well. In addition, it allows us to produce organic-inorganic hybrid polymers, thanks to its high purity and homogenity. In hybrid compositions, organic polymers bring well adhesion and flexibility whereas inorganic molecules brings hardness. With these compositions, various functions such as thermal and chemical stability, antibacterial property, hardness, anti scratch, anti wear, wettability... etc, can be reached. In addition, hybrid coatings can easily be bonded to ceramic or glass surfaces, thanks to their covalent binding property. Organofunctional silanes are the most suitable precursors for the preparation of organic - inorganic sol gel films. Alkyl groups which contain a functional groups such as epoxy, amino or vinyl are employed as cross linking agents in polymerization reactions. Meanwhile, non reactive groups of precursors do not participate polymerization reactions and they form porous structure in the silica network. This porous structure controls optical and mechanical properties of the films such as fracture or cracking. Since, the final product may have various characteristics depending on chemical composition of precursors, hydrolysis time, the addition order of materials into solution,etc..,sol-gel method requires close monitoring of each step. In this study, various compositions containing (3-glycydyloxypropyl)trimethoxysilane (GLYMO), Titanium(IV)isopropoxide and AgNO3 were prepared by sol-gel process. It is well known from the literature, coatings having Ag+ on the surface present antibacterial properties. An experimental design of 27 different compositions were prepared by changing the amount of titanium(IV)isopropoxide, hydrolysing water and hydrolysis time. Glass substrates were coated by sol-gel dip coating method at 15 cm/min withdrawal rate. Wet coatings were cured in oven at 150°C for 30 min. For all set of coating compositions, physical tests such as, pencil hardness test, linear abrasion test,adhesion test and nanoindentation tests were employed to find the most scratch resistant coating. The effect of the amount of last hydrolysing water on gel formation was investigated by percent solid test. From the exprerimental design set, it is found that, as the amount of Titanium(IV)isopropoxide decreases, the transparency and scratch resistance of the coatings decreased as well. For all the samples, a trend of decrease in solid % according to the increase in the amount of last hydrolysing water was obtained. Coatings which have high transparency were selected. Hydrolysis and polymerisation reactions of coating solutions and thin films were investigated by FTIR and silver absorbance during redox reactions were followed by UV absorbance spectroscopy. Micro and nano structural characterization of coatings were analyzed by SEM-EDS and AFM. Viscosity measurements in specific periods were done to determine the shelf life of the coating solutions. As a result of physical tests, the hardest and the most transparent samples were chosen to improve their easy to clean property. Fluorosilane was added to the most scratch resistant coating composition in two different route and easy to clean property of the coatings was determined by contact angle measurements. The anti bacterial activity of the coatings against Gram negative Eschericia Coli (E.Coli) and Gram positive Staphylococcus Aureus (S.aureus) was examined. Consequently, antibacterial (log5), scratch resistant (8N), and easy to clean (CA = 98-108°) multi-functional sol-gel coatings were developed.
Elektroforetik depozisyon yöntemiyle nano hibrit fotokatalitik filtre üretimi
Air pollution is one of the most serious problems that threatens human life on the globe. Hundreds of cities suffer from the pollution with exceeded air pollution threshold values. Hence, the pollution is counted to be one of the major reasons behind lung cancer, asthma, cardiovascular dieseases and etc. Not only outdoor air pollution but also the condition in indoor environments is critical since indoor air quality additionally affects quality of human's life and comfort. Time in daily lives, which is spent in indoor environment such as houses, offices, shopping malls and vehicles increases day by day. Particulate matter, dusts, viruses, bacteria, carbon oxides, nitrogen oxides and volatile organic compounds are among the contaminants in the indoor environment. Volatile organic compounds (VOCs) such as ethanol, toluene, benzene are major effective chemical contaminants that people breath. They are emitted from different sources, established buildings, new and renovated buildings, school, new car interiors, carpets, floor coverings, wood-based panel and furniture, solid woods, paints, cleaning products, unflued gas heaters and electric ovens, office equipments. VOCs causes health problems in a short period such as headache, fatigue, tiredness and nausea. In a long period the effect might be more serious than these problems. There are several traditional methods to remove VOCs in indoor air, however these methods are based on adsorption process from gaseous phase to solid phase. This requires frequent cleaning or periodical exchange of the filter, otherwise the adsorbed filters are going to get heavy and require replacement frequently. Photocatalytic oxidation (PCO) is comparatively a novel and promising method for the improvement of indoor air quality since the contaminants can be removed from the indoor and oxidize the water vapour and carbon dioxide (CO2) which are not harmful for human health by using a combination of semiconductor catalysts and light energy. In this study widely used titanium dioxide (TiO2) was selected to produce photocatalytic air filters. Electrophoretic deposition was preferred to immobilize TiO2 nanoparticles over polymeric and metallic substrates. TiO2 as a wideband gap semiconductor was also modified to enhance its PC activity. It is still challenge to produce visible light activated catalysts. For that various configurations, such as silver doped TiO2, silver decorated TiO2 and silver coated TiO2 nanoparticles were produced. Obtained particles were immobilized over metallic meshes via electrophoretic deposition. Finally their performance was evaluated in a custom made UV-LED based PCO reactor. High efficiency particulate arresting (HEPA) type filters are already included in recent indoors but these filters only remove particulates and particles. Consequently, PCO reactors must be developed and mounted in indoor gaseous pollutants. In this thesis, photocatalytic oxidation is capable at NF and metallic meshes based filters was designed and fabricated. As a fast and facile method electrophoretic deposition was used to coat TiO2 on these substrates and their optimization, in the filter usage area use with LED for UV light and highly efficient air filtration system with use the PCO process.
Fabrication and characterization of nickel oxide functionalized graphene oxide-polyacrylamide nanocomposites
Graphene oxide (GO) and its functionalized - modified - reduced derivatives take important place in a variety of technological applications because of their unique electrical conductivity properties and excellent mechanical properties which intrinsically come from two dimensional, sp2 bonded carbon honeycomb crystal structure of graphene and its high specific surface area (~2600 m2 g-1). Having this large surface area allow graphene to be homogenously dispersed in polymer matrix, thus it can be used to fabricate advanced nanocomposites which can be integrated in energy storage systems, physical and biological sensors, flexible electronics and many other applications. Generally, graphene oxide is produced using main three methods known as Hummer method, Brodie method or Staudenmaier method. All these three methods contain a familiar, incredibly cost-effective route; an oxidation reaction of graphite and then followed by exfoliation step to form graphene oxide. Widely accepted, oxygen functional groups on surface graphite oxide allow it to be exfoliated to form graphene oxide. However, oxygen based groups distort intrinsic graphene properties, thus reduction step is needed to yield much accurate graphene form. Several reduction routes have been studied and reported, including chemical treatment, thermal treatment, electrochemical treatment. Some of oxygen groups can be removed, but a portion will remain that can be eliminated by several reduction steps. Besides, the certain functional groups can be chemically anchored on graphene oxide surface in reduction steps. This process is described as functionalization of graphene oxide with like inorganic molecules(e.g., metal oxides) or organic molecules (e.g., polymers). Polymers have been used in many application and product because of being relatively cheaper and easily processed. However, their low mechanical and electrical properties limit their applications in some areas. Most of publication in literature has reported remarkable improvements in mechanical and electrical properties, compared to the bare polymers with a small portion of graphene filler, as crosslinker. But, an important point, the improvements intensely depend on distribution of graphene in polymer matrix and forming interfacial bondings between the graphene and host matrices. Hydrophilic polymer lead the graphene sheets to aggregate owing to interactions between the hydrophilic polymer chains and graphene layers. In contrast, graphene oxide, having oxygen based functional groups anchored on the surface, is more suitable with hydrophilic - organic polymers. However, oxygen based groups hinder intrinsic electrical properties of graphene. Hereby, grafting or intercalating of reduced - functionalized graphene oxide into polymer matrix is the most compatible option among all routes to improve its mechanical and electrical properties, simultaneously. This work has focused on fabrication of nickel oxide functionalized graphene oxide - polyacrylamide nanocomposites, (NiO/GO)n/PAAM, and investigation of their structural, mechanical, electrical properties and self-healing ability. The aim of this study is to observe the effect of nickel oxide functionalized graphene oxide (NiO/GO) amount on structural, mechanical, electrical properties and self-healing ability of nanocomposite samples and compare them with that of (BIS) crosslinked (PAAM) samples to determine the difference between (NiO/GO) and (BIS). In the first step, (NiO/GO)n/PAAM and (BIS)n/PAAM samples were fabricated by using in-situ polymerization of polyacrylamide in presence of (NiO/GO) and (BIS), seperately. Secondly, structural characterization of (NiO/GO)n/PAAM nanocomposite samples were investigated by FTIR analysis and XRD to confirm the nanocomposition and crystal structure occured. After structural correction, mechanical properties, electrical properties and self-healing abilities of (NiO/GO)n/PAAM nanocomposite samples were determined and discussed.
Design simualtion and analysis of piezoresistive microcantilever for biosensing applications
In the past decade, several research works demonstrated the ability of Biological Microelectromechanical System (Bio-MEMS) biosensors to detect of biomolecules such as Deoxyribonucleic Acid (DNA), proteins, Bacteria and Antigens. But due to the low concentration of the analytes that need to be detected in the samples,a minuscule signal results in the output of the sensor. In response to this, a need arisen for an optimized biosensor capable of giving high output signal in response the detection of few analytes in the sample; the ultimate goal is being able to convert the attachment of a single biomolecule into a measurable quantity. For this purpose, MEMS microcantilevers based biosensors have emerged as a promising sensing solution because it is simple, cheap, highly sensitive and more importantly does not need analytes optical labeling (Label-free). Among the different microcantilever transducing techniques, piezoresistive based microcantilever biosensors seem to be a more attractive solution being cheap, high sensitive, miniature, works well in liquid environments and having integrated readout system. Even though there are many publications in literature that concentrated on increasing the piezoresistive microcantilevers sensitivity, they only considered in optimizing few design and process parameters thus the resultant sensitivity enhancements are not good enough for practical applications. After the analyzation of the work found in literature, it was found that the parameters/approaches that be can be optimized/used to enhance the sensitivity of Piezoresistive microcantilever-based sensors are: Cantilever dimensions, Cantilever Material, Cantilever Shape, Piezoresistor's material, Piezoresistor's doping level, Piezoresistor's Dimensions, Piezoresistor's position, Stress concentration Region's (SCR) shape and position. In this study, after a systematic analyzation of the effect of each design and process parameters on the sensitivity, a step-wise optimization approach was developed in which almost all these parameters were variated one at each step while fixing the others to get the maximum possible sensitivity at the end. Throughout this work, COMSOL Multiphysics 5.0, a commercial Finite Element Analysis (FEA) tool, was used to simulate the sensor performance. At each optimization step, the goal was to optimize the parameter in such a way that it maximizes and concentrates the stress in piezoresistors region for the same applied force thus get the higher sensitivity. In total, almost 46 different simulations were done to get the final optimized sensor. Starting with a rectangular cantilever, the piezoresistor material and doping level were optimized in two steps. When the piezoresistor material was varied (single crystal silicon and Poly-silicon), it was found that the ΔR⁄R sensitivity is higher in the case of single crystal silicon. xxiv But for this sensor design, polysilicon has been chosen as the piezoresistor material because it's sensitivity does not depend on the crystal orientation, the sensor fabrication is easier, cheaper and can be realized in ITUnano laboratory. Next, by changing the doping level in the range between 1×1015 cm−3 to 1×1020 cm−3 and calculating the ∆R/R sensitivity, the doping level that will be used throughout the following simulations was determined. It was found that, 1×1018 cm−3 doping level is high enough to reduce the thermal noise effect, at the same time it does not be affected the sensitivity that much. Thus this doping level was chosen and used throughout the following simulations. Afterward, the cantilever material is varied to find the material that gives maximum stress and deflection for the same applied force. It was found that SiO2 resulted into almost 2.5x higher deflection and 1.7x higher sensitivity when compared to single crystal silicon (the starting cantilever material) case thus SiO2 has been selected as the cantilever material for this biosensor and it is used in the following optimization steps. Next, various cantilever shapes (Rectangular, Pi-shape, T-shape, Trapezoid, SteppedTrapezoid, and Triangular) were introduced, and for each shape, the dimensions were varied bearing in mind the process and device limits. The results from all these simulations were compared to find the optimized shape which gives the maximum sensitivity. During the rectangular shape microcantilever optimization step, it was found that the cantilever thickness has the highest effect on the sensor sensitivity when compared to the change in cantilever length and width. In addition to that, after the different rectangular microcantilever dimensions were optimized (length, width and thickness), the sensitivity increased 18.3x folds. Also, adding two side holes to the rectangular cantilever structure (T-shape) increased the sensitivity by 1.6 factor. Overall, for the same applied force, the trapezoid-shaped microcantilever design gave higher sensitivity (more than 46x times greater than the starting sensor sensitivity) whereas the stepped-trapezoid shaped gave the highest maximum deflection. Afterward, Stress Concentration Region (SCR) was introduced in the optimized trapezoid structure in different locations and orientations seeking for further sensitivity enhancement. From the simulations, it was found that adding a 30µ×10µm SCR rectangular hole to the optimized trapezoid structure 15µm away from the clamped cantilever edge, resulted in almost 1.6x times sensitivity enhancement which gave the best sensitivity value compared to the other positions. Regarding the normalized change in resistance to the applied force the final sensor's sensitivity equals to -1.5×10-8 Ω/Ω ⁄pN; this means that for each 1pN (10-10 g) biomolecules attach to this biosensor; the piezoresistor resistivity will decrease by 1.5×10-8 Ω. When compared to the starting sensor, the final sensor design gave 73.5x times better ΔR⁄R sensitivity and it is more sensitive than the other sensor designs previously reported in the literature. The fabrication sequence for this sensor was prepared, but due to technical problems in some of the devices found in ITUnano laboratory, the sensor has not been fabricated.
Aerosol filtration performance of nanofibrous webs produced via centrifugal spinning technique
Nanofibers are one of the important nano scale products. Owing to their large specific surface area and high porosity, they are widely investigated for filtration, energy and biomedical applications [1]. So far, electrospinning is by far the most common method for nanofiber production, but this method has some difficulties such as low production rate (~1 ml/h/nozzle) and high voltage necessity (up to 60 kV) [2]. However, the wide-spread commercial use of electrospinning is limited mainly due to its low production rate. Most other nanofiber production methods, such as melt-blowing, bicomponent fiber spinning, phase separation, template synthesis, and self-assembly, are complex and can only be used to make nanofibers from limited types of polymers. Centrifugal spinning is an alternative method for producing nanofibers from various materials at high speed and low cost. In this thesis, the centrifugal spinning method was reviewed thoroughly. An overview on the centrifugal spinning process was given, and it was compared with the conventional nanofiber production methods. In addition, the nanofiber filter media were produced via custom made lab scale centrifugal spinning machine. There are three experimental chapters presented in the thesis. At the beginning a custom made centrifugal spinning device was designed and manufactured. The system were introduced. After the manufacture, several experimental studies were performed using various polymer solutions. Especially, the studies were concentrated on thermoplastic polyurethane (TPU) nanofibers. After the morphology characterization, an optimization study on fiber diameter of TPU nanofibers was performed. The optimal process parameter levels were determined, and also the effects of these parameters on fiber diameter were demonstrated statistically. Then, the filtration performance of the produced webs were analyzed. A correlation between the fiber diameter and filtration quality has been established. It is expected that this study will leave a positive impression onto the forthcoming studies on nanofibers especially for the nanofibrous filter production.
Copper zinc tin sulfite CZT(S,Se) for solar cell applications
Over the last years, the need for renewable energy has grown day by day. Solar energy is one of the most important assets of renewable energy. The earth has proved itself as a non-infinite energy source. Climate change and global warming are warning the humanity for sustainable solutions. Renewable energy is one of those solutions that needs an urgent attention. Solar energy is one of the early corners of this subject. But the technology has to change as soon as possible. Silicon solar cells have been dominating the solar energy market since the day one. Their reliable performance makes silicon solar cells a viable asset but the availability of the raw materials is a matter of concern. They are physically fragile and heavy form makes it ungainly technology. Thin film solar cell technologies are the biggest rival on the subject to silicon, they have important advantages like being lightweight, flexible, cheap and easily manufactured. However, they cannot achieve the same performance as silicon solar cells yet. CZTS is a quaternary absorber layer material for solar cell technologies. It has several advantages like consisting of earth abundant, cheap, and non-toxic materials. Also one of the most important competitive edges for CZTS is that its structure is quite similar with CIGS and CIS. They have high-efficiency numbers to compete with silicon cells. However, they have two disadvantages. One of them is having toxic materials inside and the other one is that they are getting more expensive day by day (their cost is increasing over the last years). The screening technologies are using the same raw materials (elements) with them so the market price for those elements are getting more expensive. That makes element prices higher and higher every second. So, CZTS already has a place on market for itself. The advantages mentioned before makes CZTS attractive for scientists. In this study, CZTS ink was produced by hot injection method. Metal precursors were used in the reaction. Precursors can be listed as; Copper (II) acetylacetonate, Zinc acetylacetonate hydrate and tin (IV) bis(acetylacetonate) dibromide as cation precursors and elemental sulfur as a sulfur source were used. Oleylamine was used to dissolve the precursors and also as a surfactant for the reaction. The reaction occurred in a closed chamber under an inert atmosphere. Reactants were washed from oleylamine after the reaction. The product has been kept dispersed in toluene. Cadmium Sulfide layer was coated on samples by chemical bath deposition technique. Cadmium acetate and thiourea were used as source materials. Zinc oxide powder was produced by using zinc acetate and potassium hydroxide. The final product was kept in methanol solution to be used later as an n-type layer. Spray coating technique was utilized to coat samples with CZTS and ZnO. The molybdenum coated glass was used as the substrate. CZTS layer was coated first, followed by annealing of the film at 330 oC for an hour. After the annealing step, spin coating was utilized to coat CZTS one more time. This step is applied to reduce the roughness of the film. Annealing was then applied one more time on samples after the spin coating. CdS layer was coated onto the CZTS layer via chemical bath deposition as mentioned above. Finally, ZnO layer is deposited via spray coating. Molybdenum is used as an electrode and for the counter electrode aluminum was thermally evaporated onto the samples. Masks were used to protect the samples to be coated fully. Mo / CZTS / CdS / ZnO / Al configuration was obtained. Samples were characterized at each step to see if the films were what they are expected. Diodic plots were identified by current-voltage characterization. The final formation was showing the effects of the solar cell, producing current. To sum up, quaternary CZTS compound was produced and made into a film form successfully. Coating a CdS layer on top of the CZTS layer was achieved. ZnO particles were produced and used as an n-type layer. Solar cell layers were prepared in that order, and then it's tested against light until a working solar cell was achieved. In the study, CZTS solar cell production conditions were optimized.
Investigation of nanostructured vanadium oxides by wet chemical processing: Structural, morphological, optical, and electrochemical analysis
Material science steers the technological advancements. Even prehistoric ages are called as materials' names. Nano- and thin film materials took place of the normal/bulk materials, nowadays. Thus, in order to product nano-sized/ nano-structured materials and manipulate materials at nano scale, a new discipline is developed, which is called nanotechnology. There are many methods to produce thin films, such as chemical vapor deposition, physical vapor deposition, atomic layer deposition, spray pyrolysis, sol-gel method, etc. Among these methods, sol-gel is one of the most used method because it is economical and easy way. A wet solution, called gel, is obtained with sol-gel method, which is then deposited onto a substrate by some techniques, such as dip-coating, electrodeposition, spin-coating etc. Spin-coating technique is superior among other techniques because it leads to atomic packing in one direction. Nanofibers, which are 1D materials, are one of the most interesting materials among nanostructures due to their versatility, high surface area, high aspect ratio, high porosity, high electrical conductivity in one direction, etc. Electrospinning is most used method to produce nanofibers from lab-scale to industrial scale. However, there are many parameters effecting the characteristics of the obtained fibers in electrospinning technique. Vanadium and its oxide form has been studied for a long time due to their interesting characteristics. The reason of such great interest drawn to vanadium and its oxide forms is based on the varied oxidation states from +2 to +5 which let it form many oxide forms, and also the variability of the oxygen coordination geometries, such as octahedral, square pyramids, tetrahedral etc. These characteristics let vanadium oxides yield an impressive variety of structural and crystallographic arrangements. VO2 exhibits a semiconductor to metal transition near to room temperature, at about 70°C. V2O5 has an orthorhombic crystalline structure with a layered structure, which promises high ratio ion intercalation. Thus, it is very interesting material for electrochemical applications such as li-ion batteries, supercapacitors, sensors, etc. In this study, we prepared eight different vanadium-oxide samples (6 samples in thin-film form, and the other 2 samples in nanofiber form) from three different solutions/gels. We characterized the samples by x-ray powder diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectrophotometer (UV-Vis), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). Additionally, thermochromic properties of annealed samples were investigated. We also characterized solutions by analyzing their conductivity, surface tension, viscosity and optical properties.
Synthesize and characterization of ZnSe based type I and type II heterostructure nanostructures
Nanostructured materials are of interest because they can bridge the gap between the bulk and molecular levels and leads to entirely new avenues for applications, especially in electronics, optoelectronics and biology. When a solid exhibits a distinct variation of optical and electronic properties with a variation of particle size <100 nm, it can be called a nanostructure, and is categorized as (1) two dimensional, e.g., thin films or quantum wells, (2) one dimensional, e.g., quantum wires, or(3) zero dimensional e.g., quantum dots. QDs can be sytnhesized in core or core/shell forms due to interest and generally are made from III-V and II-VI family or semiconductors in the periodic table. The small size of quantum dots (QDs) result in an observable quantum confinement effect, defined by an increasing bandgap accompanied by the quantization of the energy levels to discrete values. This effect is accompanied by an exaltation of the coulomb interaction between the charge carriers. Once an electron-hole pair is created by the absorption of a photon, they interact with each other by means of their opposite charges, forming a quasi-particle called "exciton". The total energy of an exciton indicates the color (wavelength) of the light emitted by the quantum systems. If these excitons are confined in the core, they are called Type I and if they seperetly move around core and shell they are called Type II semiconductors. The intermediate case, in which one charge carrier is localized to the core and the other is delocalized over the whole structure, is known as type-I1/2 or quasi type-II. ZnSe based core/shell QDs exhibit novel properties, making them attractive from both experimental and practical point of view. Semiconductor QDs, typically prepared as core/shell NCs, are a class of strained materials with novel properties. In core/shell NCs, lattice mismatch induced stress between core and shell affects the structural, electronic and optical properties such as core diameter, band offsets and exciton energy. In this thesis, the synthesis of ZnSe core and ZnSe/Cd(Zn)S core/shellZnSe/CdxZn1-xS core/ternary shell and ZnSe/Cd(Zn)S/Zn(Cd)S core/multishell NCs was aimed and the NCs characterized by UV-Vis, PL, HRTEM and XRD along with obtaining strain amount in interfacial layer and calculating capped core diameter theoretically after the compressive and tensile shell deposition. The ZnSe core and the other core/shell heterostructurs were synthezed in our nanosemlab with our equipments according to the latest techniques referenced in articles. The XRD analysis used for determining the atomic and molecular structure of the produced QDs and for characterization of optical properties UV-Vis, PL analysis were done. The induced interface strain from lattice mismatch between core and shell was calculated from continuum elastic theory and applied in effective mass approximation method to obtain the corresponding capped core diameter. The calculated results were compared with diameter of bare core TEM images to obtain the amount the core stretched or squeezed after deposition of tensile or compressive shells. The stretched and squeezed amount of the capped core found to be in proportion with lattice mismatch amount in the core/shell structure.
Production and characterization of CdSe based binary/binary and ternary/binary heterostructure multi shell quantum dots
Colloidal semiconductor NCs (also known as quantum dots (QDs)) with their diameters range between 2-10 nm have gained a huge interest for both optical and electronical applications such as solar cells, light emitting diodes, lasers, fluorescence imaging and for fundamental studies over the last few decades due to their sizedependent optical, physical and chemical properties. QDs can be synthesized in core (bare) and core/shell forms in accordance to their application interest and are made from III-V and II-VI group semiconductors family in the periodic Table. Their optical, physical and chemical properties can be altered with deposition of shell on core. The introduced shell material's composition or spacer layer in multishell cause changes in charactristics of semiconductors. CdSe semiconductor is a subject of many studies due to their bright luminescence in the visible range of optical spectrum with different particle size. In this thesis, like most of investigations, the optical, physical and structural properties of CdSe based QDs is evaluated. The synthesis of CdSe bare core, CdSe/Cd(Zn)S core/shell, CdSe/Cd1-xZnxS core/ternary shell and CdSe/Cd(Zn)S/Zn(Cd)S core-multishell NCs are done at relatively low temperature. Then, the produced hetero structures are optically and structural characterized using UV-Vis, PL, HRTEM, XRD analysis. On the other hand, interfacial strain amount was obtained theoretically in order to calculate the capped core diameter changes after shell deposition. Interfacial strain effect cause the Bragg's 2Ɵ diffraction degree to slide in XRD analysis. In this phenomenon, this shift noticed toward higher degrees after capping the core with compressive shell while introducing lower compressive shell led in less shift in Bragg's 2Ɵ degrees. Another effect of capping CdSe core with shell of different composition observed in absorption and photoluminescence spectra. The red shift of absorption and photoluminescence peak is recorded in UV-vis and PL spectrum after shell deposition. Depending on the diameter of CdSe NCs, the red shift amount differs in absorption spectra. Using the exciton energy from absorption spectrum, the capped core size of the core was calculated. The conventional Brus equation used to calculate capped core diameter with the obtained exciton energy. For the first time, we substituted interfacial strain amount in Brus equation to observe capped core size changes after deposition of compressive shell. Interfacial strain amount is calculated from continuum elastic theory and core squeeze or stretch was observed after capping process. Result of the obtained theoretically capped core size were compared with the bare CdSe core size from TEM image to evaluate the accuracy of our proposed theoretic method. Logic and good overlap of the theoretical and experimental results showed the accuracy of the proposed theoric method.
Hot injection synthesis and structural and optical characterization of CdSe/ZnSe and CdSe/ZnS quantum dots
In this thesis, first of all CdSe QDs were synthesis with hot injection chemically methods, after that it coated with ZnSe, ZnS, to create type-I core/shell respectively. Then they characterized by PL, UV-Vis, XRD, and strain amount in interfacial layer was obtained and capped core diameter after tensile shell deposition and the compressive theoretically calculated. The CdSe core and relative core/shell heterostructures synthesized in nanosemlab with our equipments according to the latest techniques referenced in articles. First, the optical properties were analyzed with UV-Vis, PL, then molecular and atomic structur of the synthesized QDs were analyzed by XRD. Molarity of core QDs were challenged us due to the difficulty of counting the number of QDs in our solution. To overcome this issue the molarity of QDs were calculated theoritically from litratures and different shell molarity were tested. The interface strain from lattice mismatch between core and shell was analyzed from applied in effective mass approximation and continuum elastic theory method to obtain the corresponding capped core diameter.
Nano boyutta malzeme katkılarının betonun elektriksel direnç birim şekil değiştirme ilişkisine etkisi
Ülkemizde son yirmi yılda, depremlerin, malzeme bozulmalarının ve çevresel faktörlerin sebep olduğu hasarlar yüzünden yıkılan betonarme yapılar, binlerce insanın yaralanmasına veya hayatını kaybetmesine sebep olmuştur. Yapı sağlığının izlenmesi, can ve mal kaybının oluşmasını önlemek için hayati öneme sahiptir. Yapı sağlığını izlemek için kullanılan gerinim pulları noktasal ölçüm yaparlar, duyarlılıkları düşüktür, ömürleri kısadır, yüksek maliyetlidir. Bu çalışmada, kendi birim şekil değiştirmesini ve hasarını ölçen akıllı beton üretilmiştir. Akıllı betonu belirlemek için, farklı iletken malzemeleri farklı hacimsel oranlarda içeren karışımlar tasarlandı. Her karışımdan üretilen örneklere basınç testi uygulandı. Elektriksel direnç değişimi ile basınç birim şekil değiştirmesi arasındaki ilişki belirlendi. Basınç birim şekil değiştirmesine en duyarlı makro boyutta malzeme katkılı karışımlar ve nano boyutta malzeme katkılı karışımlar belirlendi. Bu karışımlara yarmada çekme testi ve eğilme testi uygulandı. Birim şekil değiştirmeye ve çatlak uzunluğuna en duyarlı karışım akıllı beton olarak seçildi. Akıllı beton farklı yükleme hızlarında test edildi. Sıcaklık ve nemin akıllı betona etkileri araştırıldı. Çevresel elektrot metodu ve alternatif akım etkileri araştırıldı. Elektrik akımının birim şekil değiştirmeye dik olduğu çapraz yüklemenin etkileri araştırıldı. Akıllı beton, elektriksel direnç değişimi ile birim şekil değiştirme arasında güçlü bir doğrusal ilişki verdi. Elektriksel direnç değişimi ile birim şekil değiştirme mekanizması, basınç, yarmada çekme ve çapraz yükleme testleri için tanımlandı. Gömülü elektrot metodunun çevresel elektrot metodundan daha iyi olduğu gözlemlendi. Akıllı beton doğru akım uygulamaları, alternatif akıma daha yüksek duyarlılık verdi. Uzun dönemde, birim şekil değiştirme duyarlılığı azaldı; uzun süre bekleyen ve nemi arttırmak için suya batırılmış akıllı beton, aynı yaş numunelerine göre daha yüksek bir birim şekil değiştirme duyarlılığına sahiptir. Büyük ölçekte akıllı beton numuneleri birim şekil değiştirme ile elektriksel direnç değişimi arasında güçlü doğrusal ilişki gösterdi. Akıllı beton yapı sağlığını izlemek için prefabrik ve önemli yapılarda kullanılabilir.
Development of nano-material based optical chemical sensors indicating oxygen levels in petrochemistry related workplaces
In workplaces, especially in refineries, volatile petroleum solvents are usually in the form of mixtures of alkanes, cyclic alkanes, alkenes and the aromatics. Such atmospheres which are deficient in oxygen may not provide adequate sensory warning of danger. Therefore correct and continuous monitoring of oxygen levels in such environments is quite important. On the other hand, ruthenium (II) derivatives are known as oxygen sensitive dyes and have intensively been used in the design of optical chemical sensors. Most of the ruthenium dyes suffer from leaching from host matrices due to the water solubilities. In order to provide the best host/dye compatibility we used the amphiphilic ruthenium derivatives in silicon based matrices. In this work, emission-based oxygen sensing properties of highly luminescent ruthenium (II) derivatives were tested in the presence and absence of some volatile organics. Newly synthesized two orange-red emitting alkyl branched ruthenium complexes were used along with silver nanoparticles (AgNPs) in two different silicon based matrices for oxygen sensing purposes. The sensing materials were fabricated in form of thin films and electrospun nanofibers. Ionic liquid and perfluorinated compounds were exploited as additives to enhance the response to oxygen. Oxygen induced spectral changes at 630 nm were followed for both gas phase and dissolved oxygen as the analytical signal. The oxygen sensitivities of the probes were also tested by lifetime based and kinetic mode measurements. Utilization of the amphiphilic Ru dyes in silicon along with AgNPs in the form of electrospun fibers resulted in many advantages such as enhanced long term stability, increased surface area, sensitivity and improvement in all sensor dynamics. Sensing characteristics of the offered design were tested and calibrated in the presence of vapors of benzene, toluene, ethylbenzene, hexane and xylene, which simulate refinery related work places.
Production and application of n- and p-type Si wafer using CVD method
Necessity for electricity is one of the most significant issues of present time. Rapid consume of most used underground resources made it necessary for researching the new kind of energy sources. After the increase of daily requirements and quality necessities, innovations in electric production technologies gained importance. Production of electricity from the sun is based on the principal of contacting the two sides of a semiconductor stimulated by sun and the returning of electrons which have been sent to conductivity level to their initiation locations after completing the entire circuit. Materials science which is a multidisciplinary branch could be defined as investigation and development of proper tools for providing sources for humanity. In this respect, in the scale of current thesis, production of solar cells for renewable energy obtainment using modified semiconductor silicon wafers was aimed and studied. Single crystal structured crystal wafers with semi-conductive character were modified and the stimulation of material with sun light was achieved. In order to enlighten the structures of the produced solar cells, SEM, XRD, XPS, UV-vis and profilometer calculations were carried out. In addition of structural analysis, electrical properties of the produced cells were determined. There are many remarkable factors in current study in order to benefit fully from the sunlight. By texturation, refraction of photons interacted with surface was prevented opposite to the angle they interacted. Optimum realization studies of electron-hole separation were achieved with diffusion time determination. With utilization of reflection blocker coating, absorption of rays interacted with the surface of solar cells was provided. In addition to the scientific results, with the support of İZ-KA to the current study, more attention to renewable energy in Dokuz Eylül University was gained. Thanks to the energy stations in university in scope of current project, charging the batteries of electrical devices was realized.
Antifungal hibrit kaplamaların hazırlanması ve karakterizasyonu
Bu çalışmada, polikarbonat (PC) ve polimetil metakrilat (PMMA) yüzeylere kekik yağı, karabiber yağı, kimyon yağı ve çay ağacı yağı katkılı 3-(Trimethoxsilyl)propyl methacrylate (TMSPM) ve tetraethyl orthosilicate (TEOS) bağlayıcı madde bazlı hibrit kaplamalar yapılmıştır. Hibrit kaplama yüzeyleri termal ve UV ile kürlenmiştir. Kaplanan PC ve PMMA polimer yüzeyleri Fourirer Dönüşümlü Kızılötesi (FTIR) Spektroskopisi analizi, dijital mikroskop görüntülemesi, temas açısı analizi ve antifungal duyarlılık ile karakterize edilmiştir. Kaplamasız PC için 87.84°, PMMA için 95.89° temas açısı verilmiştir. FTIR analizlerinde TEOS, kekik yağı, kimyon yağı, çay ağacı yağı ve karabiber yağı için karakteristik pikler elde edilmiştir. Dijital mikroskop görüntüleri için 2.059-49.322 µm aralığında kalınlık elde edilmiştir. Anrifungal duyarlılık testinde Aspergillus flavus küfü için ek etkili olanlar sırasıyla kekik yağı, çay ağacı yağı, kimyon yağı, TEOS ve karabiber yağı sırasını takip etmiştir. Anahtar Kelimeler: Antifungal, Silan, Esansiyel yağlar, Kaplama, Polimer
Investigation of corrosion properties of Ni matrix nanocomposite coatings produced by electrodeposition technique
This research aimed to investigate electrochemical corrosion behavior of Nickel matrix nanocomposite coatings produced by electrodeposition technique in a Watts bath containing titanium dioxide and Zinc doped titanium dioxide nanoparticles. In this study, titanium dioxide and Zinc doped titanium dioxide nanoparticles were prepared using a sol-gel method. Obtained results indicate that all synthesized nanoparticles and particle sizes were below 100 nm. Nickel matrix nanocomposite coatings were produced by using electrochemical deposition tecnique on stainless steel substrates. The Watts bath for production of nanocomposite coatings were prepared using the different amounts of titanium dioxide and Zinc doped titanium dioxide nanoparticles. Besides, applied current density on the coating performance were investigated in order to optimize the coating properties. Pure Nickel coatings were also deposited under the same experimental conditions for comparison. The structural, morphological, mechanical and corrosion properties of the Nickel matrix nanocomposite coatings were investigated. The surface morphology, elemental composition and phase structure of the nanocomposite coatings were examined by Scanning Electron Microscopy, Energy Dispersive Spectrometer and X-ray Diffraction, respectively. Obtained results show that Nickel-Titanium dioxide and Nickel- Zinc/Titanium dioxide nanocomposite coatings improved corrosion properties.
Nano malzeme içeren çimentolu kompozitlerin termal verimliliği
Her yıl buzlanma ve kar nedeniyle birçok trafik kazası olmakta, vatandaşlarımız hayatlarını kaybetmekte, maddi ve manevi büyük kayıplar yaşanmaktadır. Hava alanlarında pist buzlanması ve kar nedeniyle de kazalar olmakta, can ve mal güvenliği tehdit altında kalmaktadır. Buzlanmaya karşı yollara ve pistlere atılan tuz ve diğer kimyasallar, yol malzemesine, taşıtlara zarar vermektedir. Tuz-kimyasal atma veya küreme ile yollar-pistler sürekli ve zamanında açık tutulamamakta, buna karşın personel, araç, yakıt ve sarf maliyetleri oluşmaktadır. Ayrıca, trafiği durdurma veya yavaşlatma nedeniyle oluşan sefer iptalleri ve gecikmeler, maddi ve manevi kayıplar oluşturmaktadır. Elektrikle ısınan harcı belirlemek için, öncelikle iletken olan tüm malzemeler (13 mm çelik lif, 6 mm çelik lif, pirinç toz ve lif, bakır toz ve lif, karbon lif, çok duvarlı karbon nanotüp, nano tufal, nano grafen, nikel) kullanılarak doğru akım ile ısınma testi yapıldı. Bu sonuçlara göre en iyi ısınan iletkenler, harç içerisinde farklı hacimsel oranlarda olmak üzere 18 farklı harç karışımı tasarlandı. Her karışımdan 3 adet 5×5×2,5 cm³ prizma üretildi. Isınma testi uygulamak amacı ile referans karışımı dâhil toplam 18 farklı harç karışımı hazırlandı. 7. günde ve 35. günde elektrik verilerek ısınma testleri yapıldı. Isınma testinde elde edilen; sıcaklık artışı, sıcaklık artış hızı ve tüketilen enerji, performans parametreleri olarak kullanıldı ve puanlama sistemi geliştirildi. Elektriksel direnç değişimi ile sıcaklık artışı arasındaki ilişki belirlendi. En iyi ısınan makro ve nano boyutta malzeme katkılı karışımlar belirlendi. Elektrik ile ısınan harç, hava alanlarında, yollarda ve binaların ısıtılmasında kullanılabilir.
Fotovoltaik-termoelektrik hibrid sistemlerinin termoelektrik modüllerinin verimlerinin arttırılması
The consumption of fossil fuels outcomes to greenhouse gases that brings out global warming of the World's atmosphere and nearby to climate change. Under the surface are hidden costs such as security expenses, clean-up efforts, air pollution, environmental damage, war-related expenses and other additional hidden expenses. Sources of Renewable energy are especially very good energy sources to battle against global warming. Energy from Sun, is a shining renewable energy source, especially for the regions with high solar irradiance. After the Oil Crisis, happened in 1973, the researchers especially focuses on photovoltaics. Till now the scientists are focusing on improving the effieciency of solar cells and photovoltaic modules. PV-TE Hybrid Systems are especially one of the shining systems of new type of systems, to enhance the module efficiency. Combining photovoltaic (PV) and thermoelectric (TE) modules into PV-TE systems has shown great promise for maximizing the use of the sun's spectrum, boosting overall power output, and lowering the amount of area needed for PV power plants. With my thesis I focused on enhancing the efficiency of a practical PV-TE system model. Usually, a significant temperature differential is produced across the thermoelectric generator (TEG) module utilizing a variety of heat removal techniques in order to increase the power output of the TE component. These cooling systems makes increase, in performance of TEG module, however, concurrently, they rise the electrical performance of PV. In this thesis, I assessed the performance of PV-TE systems using seven different TEGs and monocrystalline silicon solar cells in four different scenarios. According to Standard Test Conditions EN/IEC 61215, the PV-TE hybrid systems are first tested at 25 °C without a cooling device. We then assess the systems using a passive cooling strategy, improving heat dissipation with aluminum heat sinks. Additional evaluations use an active cooling (AC) system with coolants of water and nanofluid in succession. The evaluations' findings are intended to set a standard for raising the effectiveness of upcoming PV-TE systems.
Theoretical investigation of CU based intermetallic compounds at nanoscale
Intermetallic compounds (IMCs), including transition metals and p-block metals, exhibit high resistance to oxidation and corrosion, low density, high conductivity, and magnetic polarizability. There is growing interest in intermetallic compounds (IMCs) consisting of transition metals and p-block elements, particularly aluminum (TM-Al IMCs). These alloys exhibit a unique combination of properties that make them well-suited for extreme thermal environments. Notably, they possess a favorable balance of low density and high melting temperatures, which contributes to their structural integrity and thermal stability. This thesis employs the first-principles computational approach grounded in Theory of Density Functional (DFT) to analyze the structural and electronic characteristics, charge density distribution, spin polarizability, and magnetic properties of Cu(3-x)MnxAl (x = 0, 1) intermetallic compounds. The study implemented the Perdew, Burke, Ernzerhof (PBE) exchange-correlation functional as part of the Approximation of Generalized Gradient (GGA) framework. The calculation of metallic and conductive nature and structural properties was performed simultaneously for all crystal lattices of Cu(3-x)MnxAl (L12, D03, and Heusler L21) with 221-Pm3m, 225-Fm3m space groups. Notably, the study clarifies the stoichiometric similarity and difference between L12 and D03 type structures by presenting a detailed discussion of the D03 structure and its targeted properties for the first time. The lattice constant values obtained by performing various optimizations shows remarkable consistency with previously reported theoretical and experimental measurements. Density Functional Theory-DFT calculations were utilized to analyze the electronic structurethe electronic structure, including band structure, total density and partial density of states, Major and minor spin state densities, map of charge density distribution, and Mulliken bond population. Additionally, the study investigated the chemical bonding characteristics and mechanical properties of intermetallic compounds (IMCs), such as elastic constants, elastic moduli, Pugh's ratio, elastic anisotropy, Poisson's ratio, and Cauchy pressure. The directional dependence of each mechanical property (young, bulk, shear modulus) and the corresponding mechanical properties were calculated. The electron density distribution and population analysis are consistent and reveal the dominant bonding type in each IMC. Furthermore, a Spin Polarizability analysis has been carried out to demonstrate the magnetic nature of the Cu2MnAl (L21) Full Heusler alloy upon the addition of the Mn atom.
Synthesis and characterization of carbon nanomaterial(S) by hydrothermal carbonization of various wastes
This research investigates a sustainable and resource-efficient approach to biomass waste management by synthesizing high-value carbon nanomaterials through hydrothermal carbonization (HTC). Three distinct biomass wastes: pomegranate peel waste (PPW), marigold flower waste (MFW), and cotton fabric waste (CFW), were subjected to HTC under varying conditions to explore their conversion into functional carbon-rich products. Among the tested feedstocks, PPW emerged as the most promising precursor for carbon nanomaterial production, yielding well- defined hydrothermal carbonaceous nanospheres (HCNs) with diameters ranging from 50 to 300 nm. In contrast, the carbon materials derived from MFW and CFW exhibited irregular and poorly defined morphologies. Additionally, carbon dots (CDs) displaying strong blue luminescence were successfully recovered from the liquid phase of the PPW-HTC process, demonstrating the feasibility of dual-phase valorization from a single waste stream. To assess the environmental viability of the process, a prospective life cycle assessment (LCA) was conducted. The analysis identified electricity consumption for reactor heating (75–79%) and drying (20–22%) as the dominant contributors to environmental impact. Scenario modeling indicated that replacing the current electricity mix with renewable sources could reduce abiotic depletion and global warming potential by up to 120%. Sensitivity analysis of wastewater disposal routes revealed that while switching to treatment plants offers only minor improvements at laboratory scale (<1%), the benefits become more pronounced at industrial scales. The scenario involving CD recovery (HTCa) exhibited comparatively higher environmental burdens due to full energy allocation but avoided reliance on high-purity chemical precursors commonly used in conventional CD synthesis. This strategy highlights the environmental potential of integrating biomass-based inputs and waste valorization into emerging nanomaterial production pathways, aligning with circular economy principles. HCNs demonstrated significant potential as green antioxidants. Results from DPPH and phosphomolybdenum assays revealed strong radical-scavenging activity, comparable to ascorbic acid, a standard antioxidant. These findings support the use of HCNs as a sustainable alternative to fossil-derived nanomaterials and synthetic antioxidants, offering both environmental and human health benefits. Under the assay conditions employed in this study, HCNs exhibited minimal antibacterial activity. While these results indicate limited antibacterial effectiveness at the tested concentrations, they also suggest that HCNs may be less cytotoxic, potentially supporting their use in biocompatible or non-disruptive applications. Future studies should explore their performance under varying experimental conditions or investigate modifications to enhance antibacterial efficacy. In addition, the study evaluated the application of HCNs in cement composites. Incorporating HCNs resulted in improved workability and enhanced flexural strength in certain samples, along with a reduction in density without significant compromise in compressive strength. The method of HCNs incorporation was found to significantly influence the final properties of the composites. Although the sustainability impact of low-dosage additions is limited, these findings show the potential of HCNs as a useful addition in cement-based systems, suggesting the need for further research and optimization—particularly when combined with other sustainability-enhancing materials.
Development of high temperature tribological features of electroless nib and NiB/Al2O3 nanocomposite coatings
This study examines the microstructural, mechanical, and tribological performance of electroless NiB and NiB-Al2O3 coatings applied to mild steel (St-37) substrates. In this dissertation, the electroless NiB and NiB-Al2O3 coatings were deposited onto the steel substrates to produce homogeneous microstructures using the electroless deposition method. The effects of electroless deposition parameters on the microstructure and the friction behaviours of the coatings were investigated in detail. A temperature-controlled wear testing setup was employed to evaluate their high-temperature tribological behavior. The investigation specifically explored the influence of Al2O3 nanoparticle concentration, the configuration of the wear test, and the testing temperature on the dominant wear mechanisms of the coatings. Tribological testing was carried out to assess the performance of the coatings under varying thermal conditions. The tests were conducted at four distinct temperatures: 25 °C (room temperature), 200 °C, 400 °C, and 600 °C to evaluate the influence of elevated temperatures on the friction and wear characteristics of the coatings. A ball-on-disk configuration was utilized for providing controlled and consistent test conditions. During the experiments, a constant applied load of 3 N was applied to simulate realistic contact pressures typically encountered in practical applications. By systematically increasing the temperature, the study aimed to observe and analyze how thermal effects, and changes in material properties, impacted the tribological behavior of the coatings. The results provided valuable insights into the coatings' ability to maintain wear resistance and frictional performance across a wide range of operating temperatures. The experimental findings revealed that the electroless NiB-Al2O3 nanocomposite coatings consistently demonstrated a lower wear rate across all tested temperatures compared to the electroless NiB coatings without Al2O3 reinforcement. This enhanced wear resistance was attributed to the incorporation of Al2O3 nanoparticles, which significantly improved the coatings' ability to withstand wear under varying tribological conditions. Detailed characterization of the microstructures of the coatings, worn surfaces, and wear mechanisms was carried out using advanced analytical techniques, including Scanning Electron Microscopy (SEM) for observing surface morphology, Energy Dispersive X-ray Spectroscopy (EDS) for elemental analysis, X-ray Diffraction (XRD) and Raman Spectroscopy for chemical and structural identification. These techniques provided a comprehensive understanding of the tribological behavior of the coatings and the role of Al2O3 in improving their performance under high-temperature conditions.
Preparation of polybenzoxazine-EPDM rubber based hydrophobic nanocomposite materials
The aim of this thesis is to prepare a hydrophobic nanocomposite with Polybenzoxazine (PBZ) and ethylene-propylene-diene-monomer rubber (EPDM) filled by nano titanium dioxide (TiO₂) and polytetrafluoroethylene (PTFE/Teflon). In this work, the first step in the process is to synthesize fluorine-containing PBZ. Fluorine is intended to contribute to hydrophobicity of the PBZ. PBZ was synthesized by ring-opening polymerization, catalyzed by dimethyl amino ethanol (DMAE) base catalyst using benzoxazine monomer obtained from 4-hydroxy benzaldehyde, 2-(trifluoromethyl)aniline and paraformaldehyde. In order for the PBZ polymer to be ring-opening polymerization to take place, the reactants were magnetically mixed in an oil bath at 100 °C for 24 hours. As a result of polymerization, a hard brittle, light-yellow color solid polymer was obtained. Since the synthesized PBZ is a hard and brittle polymer on its own, it is necessary to get help from another polymer to improve the elasticity for polymer nanocomposite samples. Thus, it was prepared a blend with PBZ and EPDM rubber. Polymer nanocomposite samples with weigh ratios of 40% EPDM and 40% PBZ blend matrix, 10% nano TiO2 and 10% PTFE additives were prepared. Since at least one of the fillers must be nano-sized in order to meet the condition of being a nanocomposite, 0-20 nanometer TiO2 additive is used. Both nano TiO2 and PTFE additives helped to prepare a hydrophobic polymer nanocomposite. Since one of the matrix components is EPDM rubber, some of the samples were cross-linked with 0.1% sulfur by weight to perform the vulcanization step, which is an important step in the use of rubber material. Polymer nanocomposite samples prepared with and without sulfur were heated and cured with temperatures of 25 °C, 100 °C, 150 °C and 180 °C, respectively. The effect of sulfur and curing temperature on the hydrophobicity of polymer nanocomposite samples was studied. The EPDM-PBZ nanocomposites were also characterized by UV-vis., TGA-DTA, SEM, SEM-EDX, FTIR, contact angle measurement characterizations. The contact angle was noted as 101.1° for PBZE1-EPDM-PTFE-Nano TiO2 nanocomposite sample. According to the UV results, the samples showed wide range abroad absorption peaks. According to all test results, the preparation of a hydrophobic polymer nanocomposite was successful. It was observed that the additives were homogeneously distributed in the matrix, there was no agglomeration. When the prepared polymer nanocomposites were compared to whether they were hydrophobic or not, it was clearly seen that the temperature and the curing process by cross-linking with sulfur increased the hydrophobicity in the samples. In particular, the EPDM-PBZ polymer nanocomposite sample with sulfur, vulcanized at 150 °C presented better hydrophobic features with a contact angle of 110°.
Development of lithium-oxygen battery nanostructured electrodes facilitated by M13 virus and plant extract
Lithium-oxygen (Li-O2) batteries are a promising candidate for next-generation rechargeable battery systems due to their superior theoretical energy densities (11,586 W h Kg-1), which is near to those of gasoline (11,860 W h Kg-1). The principle of Li-O2 cell is relied on the formation of Li2O2 by the interaction between Li cations and oxygen (from the air) during discharge at the cathode surface and decomposition of Li2O2 upon charging. Therefore, the highly stable and reversible electrochemical reactions in Li-O2 cell is dependent on accelerating formation and decomposition of Li2O2. One solution to solve this issue is selecting an appropriate cathode catalyst with high porosity, good electronic conductivity, chemical stability, and high catalytic activity. In this thesis, our purpose is to develop novel efficient cathode materials for Li-O2 batteries using non-aqueous electrolytes by utilizing bio-inspired materials such as plant extract and M13 viruses. The M13 virus is a phage that infects bacteria but is harmless to humans and serves as a bio-template due to its unique morphology. Plant extracts are a rich source of bioactive chemicals. They have been demonstrated to be promising as reducing and capping agents for the biosynthesis of a variety of metal/metal oxide nanoparticles. Therefore, TiO2 nanoparticles with a cauliflower morphology were synthesized by using chamomile extract. Bio-TiO2 electrode containing 5 wt.% carbon black, showed a large overpotential and 30 stable cycles at the limited capacity of 500 mAhg-1. Therefore, to increase the cycle life of the Bio TiO2, a core-shell-like structure was formed with α-MnO2 as a shell, and the content of the carbon black was increased from 5 wt.% to 10 wt.%. The obtained TiO2/α-MnO2 showed 60 stable cycles at the limited capacity of 600 mAh g-1. However, 10 wt% carbon black caused the formation of by-products and limited the cycling behavior of the cathodes. As a result, to increase the electrical conductivity and catalytic activity of metal oxides without using carbon additives, the unique one-dimensional α-manganese oxide nanowires incorporated with ruthenium nanoparticles were constructed with the assistance of M13 bacteriophage. The virus templated Ru/α-MnO2 nanowires offered a high porosity and an extensive surface area as a cathode material. This cathode demonstrated a high capacity of 14,383 mAh g-1 with 48 stable cycles at a limited capacity of 1000 mAh g-1. In conclusion, these biosynthesis methods could provide an eco-friendly and cost-effective approach to develop high-performance battery electrodes. The design strategy manufactured in this thesis could be applied not only to batteries but also to other applications, which require nanoscale materials.
M13 virus template as a new approach to electrochemical energy storage in Li-O2 breathing battery cathodes
Due to high potential energy densities of lithium-oxygen (Li-O2) batteries (11,140 Wh kg-1) have been explored as one of the most promising energy storage systems for the future generation of state-of-the-art batteries. During discharge, oxygen (from the atmosphere) is reduced at the cathode (Oxygen reduction reaction, ORR), where it reacts with lithium ions released from the lithium metal anode to generate Li2O2, and the discharge residue decomposes during charging (Oxygen evolution reaction, OER). Cathode catalysts significantly improve ORR/OER and the electrochemical stability of Li-O2 systems. To accelerate ORR and OER in Li-O2 cells, a suitable air cathode architecture must possess sufficiently porous distribution to allow oxygen diffusion, high conductivity to transfer lithium ions, chemically stable, and highly catalytic activity. Therefore, we first report metal nanoparticles (e.g., Pd and Ru) and α-manganese oxide nanowire supported by reduced graphene oxide. In the Li-O2 cathode, noble metals are used as oxygen evolution reaction (OER) electrocatalysts to minimise charge overpotential and provide stable cycling performance. MnO2 is an appealing, useful transition metal oxide catalyst in Li-O2 batteries due to its cost effective, high catalytic activity, and good oxygen reduction characteristics. In the first experiment, Ruthenium nanoparticles were incorporated on MnO2 surfaces, and then the mixture was applied to 50% graphene via ball milling. This electrode demonstrates the charge overpotential and stability up to 40 cycles at a limited capacity of 800 mAh g-1. The produced rGO@Pd@α-MnO2 hybrid nanocomposite cathode delivered a full discharge capacity of 7500 mAh g-1 and maintain cycle life upto 50 cycles with a low discharge/charge potential gap of 0.4 V. Our result shows higher stability of Pd despite Ru. Furthermore, graphene-based electrodes with different graphene content (e.g. 100%, 75%, 50%) were prepared, and by reducing graphene, the higher performance of Li-O2 cell was obtained due to preventing side reactions. On the other hand, plant extract and M13 virus were utilized for the reduction of graphene oxide and preparation of MnO2 nanowires, respectively. Using these biomaterials assist in designing advanced nanomaterials through a green and biocompatible process. Overall, the synergistically effects of α-MnO2 nanowires and metal nanoparticles are combined in this study by decorating graphene sheets to boost cyclability and capacity, resulting in highly efficient Li-O2 cell performance.
Lityum iyon piller için yüksek kapasiteli LiFePO4/C/rGO nanokompozit pozitif elektrot
The development of new electrode materials with superior electrochemical capabilities, primarily dictated by the cathode materials, is required for widespread and extended applications of Li-ion secondary batteries. Because of its excellent stability, availability, and environmental friendliness, LiFePO4 (LFP) is widely recognized as a viable cathode material. This study used a low-cost iron (III) as the base material to manufacture single-phase LFP material with submicron particles using a simple solution combustion process based on the glycine–nitrate technique. The optimal Glycine to LiFePO4 ratio was found to be as 1:4 to produce high purity LiFePO4 and produced LiFePO4 showed 102 mAh/g discharge capacity at the constant rate of C/20. Sucrose was utilized as a carbon source to obtain carbon-coated LiFePO4 powders. The discharge capacity of the as-prepared LiFePO4/C sample with 12% carbon content is around 157 mAh/g at a 0.1 C rate and 88 mAh/g at a 5 C rate. Furthermore, throughout the 50-cycle at varying current rates, the electrodes showed excellent cycling performance. To enhance the capacity of carbon-coated LiFePO4, different amount of Graphene was reinforced to the cathode material. The carbon-coated lithium iron phosphate with 4 wt.% graphene showed a specific capacity of 197 mAh/g. The highly conductive graphene flakes wrapped around carbon-coated lithium iron phosphate enhance electron migration during charge and discharge operations, decreasing irreversible capacity during the first cycle and resulting in a coulombic efficiency of 99% at varied C-rates.
Development of nanocomposite biodegradable film containing iron nanoparticles biosynthesized by Saccharomyces cerevisiae
The present study has sheds light on the synthesis of iron oxide nanoparticles (IONPs) by Saccharomyces cerevisiae yeast as a green method by using the components of yeast cell walls as reducing agents to promote more beneficial effects in life applications. The main objective of the study is to examine the antimicrobial and mechanical properties of whey protein based edible films contained IONPs. At the present study, IONPs were synthesized by using S. cerevisiae from iron chloride (FeCl3) precursor at three different concentrations (0.5, 1.0, and 1.5 mM). These iron oxide nanoparticles and lysed yeast cells residue (YSR) were used with whey protein concentrate and glycerine to prepare nanocomposite edible films contained 0, 0.25, 0.5 and 0.75 mM IONPs. The results have shown successful synthesis of IONPs as hematite (Fe2O3) according to the XRD analysis with crystal average size (24-35 nm), while FTIR spectrum indicated the presence of IONPs with the protein matrix of the films. The FESEM images have shown the presence of nanomaterials in range between 43 and 127 nm. The films have shown zero inhibitory effects against the growth of tested bacterial strains. Tensile strength (TS) of the films containing 0.5 mM and 0.75 mM IONPs increased significantly (P<0.05) compared to the control films (without IONPs). E% at break and water vapor permeability of the films with IONPs decreased significantly (P<0.05) when compared to WPC films with no IONPs. The colour change (∆) was increased significantly (P<0.05) in IONPs contained films as well as the whiting index and yellowing index. In conclusion, incorporative IONPs into whey protein film showed no influence as antibacterial agent. Yet, IONPs enhanced the mechanical properties of whey protein based edible films.
Nano silicon reinforced carbon anodes for high-capacity lithium ion battery: State of charge (SOC) and battery life time testing
The importance of active materials for anodes has gained significant attention in recent times. Carbonaceous materials are typically used as anode candidates in lithium-ion batteries (LIBs), but their low theoretical capacity of 372mAh/g restricts their applications in advanced LIBs. Therefore, Silicon (Si) is considered a prominent alternative anode material for LIBs to replace graphite. Since the theoretical capacity of Si is ten times higher than graphite; however, it suffers from massive mechanical deformations induced during cycling. For this purpose, composites of Si-graphite are proposed for better cycling performance and increased specific capacity. Herein, nano Si powder (<100nm) containing mesocarbon microbeads (MCMB) composites are prepared, and their rate capabilities as anode material for LIBs have been investigated at different current densities. Diverse compositions of the active anode materials (Si and MCMB), carbon black (CB), a binder sodium carboxymethylcellulose (CMC-Na), and distilled water as a solvent have been utilized for the fabrication of anodes, and the fabricated anodes have been morphologically and electrochemically characterized. Moreover, the state-of-charge (SOC) analysis has been evaluated by setting three different upper and lower cut-off voltages. Our analysis revealed that a composite comprising the lowest Si content (5wt%) exhibited better rate performance and retained a capacity of 455mAh/g after 60 cycles. 15wt% Si showed the worst rate capability performance. Similarly, in theSOCanalysis,a moderate voltage window between 1-0.05V was found optimalon the basis of rate capability results. Voltage window between 1-0.07V lead to quick capacity loss and large surface cracks confirmed in FESEM images. Additionally, in the SOC analysis, 5wt% Si showed the best cycling performance and lost only 10% of its capacity at 1C and 13% at C/2 after 200 cycles between 1-0.05V.
Nanoyapılı Pt ve Pt-Ag alaşımlarının üretimi, karakterizasyonu ve hidrojen gaz algılama özelliklerinin incelenmesi
This thesis presented hydrogen (H2) sensing properties of platinum (Pt) and platinum-silver (Pt-Ag) thin films. Pt and PtAg films were deposited on glass substrate by magnetron sputter technique. The Pt thin films with different thickness (2-50 nm) were prepared using RF sputtering method. The thicknesses of the films were controlled by a piezoelectric sensor placed in sputter system at the same time of coating process. On the other hand in this study, 3 nm PtxAg1-x (x: 0.95, 0.90, 0.80 and 0.50) thin films were coated by co-sputtering technique. The structural properties of Pt and PtAg alloy films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) techniques. Hydrogen sensing properties of the Pt and PtAg films were investigated depending on film thickness, temperature and concentration. Temperature dependent resistances and the gas measurements of the Pt and PtAg thin films were studied under a dry air flow and hydrogen ambient at a temperature range from 30 °C to 200 °C. Thus the best working performances of Pt and PtAg sensors were detected. The results showed that the resistance is directly proportional with temperature, and inversely proportional with the thickness of Pt thin film sensors. The H2 sensing properties of Pt thin film sensors were examined in the concentration range of 0.1 % - 1 % H2. Among the results for Pt thin films, it was revealed that the Pt thin film with 2 nm thickness exhibited the best sensing performance to H2 at 30 °C under dry air flow. The best response time was obtained at high temperatures for Pt thin film sensors. H2 sensitivity of PtAg sensors were also investigated in the concentration of 25 ppm - 1000 ppm H2. The resistances and the sensitivities of PtAg thin film sensors were increased with enhancing the temperature. Among the results for PtAg sensors, 3 nm Pt0.80Ag0.20 sensor showed the best sensitivity properties at 150 oC.
Optoelekrtonik uygulamalara yönelik nano malzeme destekli florofor, fosfor veya fosfor karışımlarının polimerik matriksler içerisinde incelenmesi
In this thesis we investigated the interactions between the commercially available LED phosphorus and nano-scale materials or dyes in terms of their emission abilities in polymers. In the first part of the thesis, photoluminescence of the Eu2+ doped Ca-α-Sialon (Ca-α-SiAlON:Eu2+), Ce3+ doped lutetium aluminum garnet (LuAG:Ce3+) and their binary blends with the quinine sulphate (QS) were investigated by steady-state and decay time measurements. The Ca-α-SiAlON:Eu2+ exhibited 44% increase in the intensity when blended with the QS. Similarly, the binary blend of QS-LuAG:Ce3+ exhibited 98% enhancement in the intensity. Excited state lifetimes of the phosphors were also studied in nanosecond and microsecond time scales, respectively. Spectral data presented some evidence for the donor-acceptor relationship of the QS/ Ca-α-SiAlON:Eu2+ and QS/LuAG:Ce3+ counterparts where the QS was the donor. The offered phosphor blends, exhibited enhancement in the optical brightness without any spectral shift. In the second part of the thesis, CO2 sensitive HPTS dye was used along with the bioactive glasses and ionic liquid. The bioactive glasses equipped with the rare earths of Er3+, Tb3+ and Er3+and Tb3+, were chosen due to their porous structure, optical transparency and intrinsic fluorescence. After spectral characterization steps we exposed the composites towards varying concentrations of the CO2 and recorded the intensity based response both in steady-state and kinetic mode. We also determined the decay times in the absence and presence of the CO2. We obtained promising results from the studies performed by using the bio-compatible bioactive glasses in terms of enhanced optical brightness and CO2 sensitivity.
Biyosensör uygulamaları için karbon nanotüplerin sentezi ve karakterizasyonu üzerine araştırmalar
In this thesis, production optimizations of CNTs were carried out with the CVD method, which is a practical and cost-effective method. In the CVD method, a cause-effect relationship was established between the properties and process parameters that determine the final morphology, such as substrate type, catalyst type, catalyst concentration, growth time, and processing temperature. In the first stage, five different catalysts, four different substrate types, three different growth times, three different catalyst concentrations, and three different growth times were applied. As a result, the most efficient tubular performance was obtained on the Si wafer substrate at one thousand degrees Celsius processing temperature by applying growth times of three, five, and seven minutes with the help of iron-based catalysts. Data from SEM samples showed that the lowest tube diameter was acceptable nanoscale. With EDX analysis, it has been shown that as the catalyst concentration increases, the carbon efficiency decreases, confirming the results of the SEM analysis. The highest carbon percentage was determined in the sample with the lowest catalyst concentration. The specific peak attributed to sp2 hybridization of CNT carbon in FT-IR analysis was observed in all sample. CNTs, which are targeted for use in biosensor applications, are desired in terms of their high defect structure and faster interaction with chemical and bioactive species. The Raman spectra confirmed that this goal was achieved with the I_D/I_G ratio of the obtained CVD-based CNTs. XRD graphs showed that the expected graphitic peak for an ideal CNT was obtained for all samples. In XPS spectra, it was observed that the sp3/sp2 ratio increased with increasing catalyst concentration. The current-voltage characterizations revealed that all measurements were close and consistent, as well as high potential in a biosensor application. As a result, it has been proven that the properties of CNTs, which are the output of this thesis, can be improved for use in biosensors by controlling the production parameters. In this thesis, production optimizations of CNTs were carried out with the CVD method, which is a practical and cost-effective method. In the CVD method, a cause-effect relationship was established between the properties and process parameters that determine the final morphology, such as substrate type, catalyst type, catalyst concentration, growth time, and processing temperature. In the first stage, five different catalysts, four different substrate types, three different growth times, three different catalyst concentrations, and three different growth times were applied. As a result, the most efficient tubular performance was obtained on the Si wafer substrate at one thousand degrees Celsius processing temperature by applying growth times of three, five, and seven minutes with the help of iron-based catalysts. Data from SEM samples showed that the lowest tube diameter was acceptable nanoscale. With EDX analysis, it has been shown that as the catalyst concentration increases, the carbon efficiency decreases, confirming the results of the SEM analysis. The highest carbon percentage was determined in the sample with the lowest catalyst concentration. The specific peak attributed to sp2 hybridization of CNT carbon in FT-IR analysis was observed in all sample. CNTs, which are targeted for use in biosensor applications, are desired in terms of their high defect structure and faster interaction with chemical and bioactive species. The Raman spectra confirmed that this goal was achieved with the I_D/I_G ratio of the obtained CVD-based CNTs. XRD graphs showed that the expected graphitic peak for an ideal CNT was obtained for all samples. In XPS spectra, it was observed that the sp3/sp2 ratio increased with increasing catalyst concentration. The current-voltage characterizations revealed that all measurements were close and consistent, as well as high potential in a biosensor application. As a result, it has been proven that the properties of CNTs, which are the output of this thesis, can be improved for use in biosensors by controlling the production parameters.
Organik-inorganik hibrit nanokompozit malzemenin hazırlanması, karakterizasyonu, optimizasyonu ve uygulaması
Kurkumin, zerdeçal (Curcuma longa) köklerinde bulunan ve antioksidan, antienflamatuar, antimikrobiyal ve antikanserojenik aktiviteler sergileyen doğal bir polifenoldur. Kurkumin sahip olduğu olağanüstü biyolojik özellikleri nedeniyle farmasötik açıdan ilgi çekici bir terapötik ajandır. Bu umut verici biyomedikal özelliklere rağmen, serbest kurkumin moleküllerinin sudaki çözünürlüğünün az olması nedeniyle klinik etki ve biyoyararlanımı düşüktür. Bu nedenle, çözünürlüğünü ve biyouyumluluğunu arttırmak için ilaca uygun bir dağıtım sistemi sağlamak esastır. Bu çalışmada, nanokompozit malzemelerin sahip oldukları üstün özellikler ile moleküler baskılanmış polimerlerin kompozitlere kattığı yüksek seçicilik, mekanik kararlılık, tekrar kullanılabilirlik gibi üstün özelliklerinden yararlanılarak kurkuminin spesifik bağlanması ve kontrollü salımı için karbon bazlı moleküler baskılanmış nanokompozit ilaç dağıtım sistemi geliştirilmesi hedeflenmektedir. Bu amaçla, fonksiyonel monomer olarak kitosan ve derin ötektik çözücü ve fulleren kullanılarak hazırlanan CTS-DES-FUL@MIP nanokompoziti, deneysel tasarım ile dizayn edilmiş ve miniemülsiyon polimerizasyonuna göre sentezlenmiştir. Sentez parametrelerini etkileyen sekiz değişkenin (kitosan miktarı, fulleren miktarı, SDS hacmi, karıştırma hızı, sıcaklık, çapraz bağlayıcı miktarı, hegzadekan miktarı ve DES miktarı) taranması Plackett-Burman tasarımı ile yapılarak kurkuminin adsorpsiyonu için önemli olan parametreler belirlenmiştir. Daha sonra bu parametreler, tepki yüzeyi metodolojisi ile optimize edilmiştir. Ayrıca, optimize koşullar altında sentezlenen CTS-DES-FUL@MIP nanokompozitinin spesifik bağlanmasının belirlenmesi amacıyla adsorpsiyon parametrelerinin optimizasyonu ve adsorpsiyon performansı incelenmiştir. CTS-DES-FUL@MIP nanokompozitinden kurkuminin kontrollü salımı, simüle edilmiş gastrointestinal sıvılarında inkübasyon yöntemiyle araştırılmıştır. CTS-DES-FUL@MIP nanokompozitinden 120 saatlik sürenin sonunda salım %96,90 oranında gerçekleşmiştir. Buna dayanarak, baskılama işlemine bağlı olarak kurkumin ile CTS-DES-FUL@MIP nanokompozitin fonksiyonel monomerleri arasındaki yüksek spesifik etkileşimler nedeniyle uzun sürede salımın gerçekleştiği söylenebilir. Sonuç olarak, sentezlenen kurkumin baskılanmış polimerin kurkumin için etkili bir taşıyıcı olabileceği söylenebilmektedir.
Epoksi termoset polimer sistemlerin mekanik karakteristiklerinin nanoyapılar kullanılarak geliştirilmesi
Epoxy thermoset polymer composites are extensively utilized in a variety of industries, including the automotive, aviation, space, marine and electrical-electronic industries due to their outstanding mechanical, chemical, thermal, and electrical properties. However, since the neat epoxy intrinsically has a brittle structure, it should be incorporated with various particles to improve the fracture resistance and toughness. In this study, silica particles varying with different particle sizes and filler contents were used to prepare diglycidyl ether of bisphenol-A (DGEBPA) epoxy composite cured with methyl tetra hydro phthalic anhydride (MTHPA) to examine the impact of filler content and particle size on the composite's fracture behaviour. In accordance with ASTM-D5045 standard, linear elastic fracture mechanics were used to describe the fracture behaviour of composite materials. It was concluded that the fracture toughness increases with increasing particle size at the micro dimension but decreases inversely when shifted towards the nano dimension. The fracture surfaces were examined by SEM imaging technique, and toughening mechanisms were defined depending on the silica particle size and content. Before the fracture mechanics test studies, a time temperature transformation (TTT) diagram was constructed for the existing epoxy composite system, which can be used as a tool for the optimization of the process parameters.
ZnO nanoyapıların üretilmesi, karakterizasyonu ve uygulama alanlarının araştırılması
It is common knowledge that zinc oxide (ZnO) as a substantial semiconductor material because of its broad band gap (3.37eV) and good seperation energy (60 meV). Anodic oxidation of ZnO molecules have drawn interest because of their cost-effective synthesis, high efficiency and simplicity of the process. Anodization parameters (voltage, time, ph, electrolyte) can influence the morphology of ZnO. Also, ZnO is widely used in several implementations such as photovoltaic cell, chemical sensor, antibacterial agent and photocatalysts. Structures and different morphologies of ZnO can exert influence on its photocatalytic activity. In this thesis, ZnO nanostructures were produced succesfully through anodic oxidation method. Before anodization, a large portion of bulk Zn was cut off into nine pieces with dimensions 3x3 cm2. These samples were sanded up to acquire the appropriate material surface. After that, samples sonicated in ethanol, acetone and deionized water in an ultrasonic bath for ten minutes separately. Produced ZnO samples were heat treated at 300 °C for one hour with the heating rate of 5 °C/minute. The synthesized ZnO nanostructures were characterized to investigate their structure, elemental composition, photocatalytic activity and morphology with aid of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and UV-Vis spectrophotometer. Concludes from this produced ZnO specimens can make use of as photocatalyst.
Termal analizler için mikro ve nano yapılı aygıtlar
The recent advent of micro and nano devices increased the interest in small scale material properties, such as elasticity, conductivity or heat capacity, which are considerably different from their bulk counterparts due to, primarily, increasing surface to volume ratios. These novel properties must be analyzed by using ultra-sensitive devices since characterization of these properties is not possible with conventional probing instrumentation due to their large mass or volume which decreases signal to noise ratio. Microelectromechanical systems (MEMS) with short response time and high sensitivity are suitable for such measurements, such as very small mass detection (zeptograms) and calorimetry of small volume materials (yoctocalories).In this thesis a MEMS cantilever was used for thermomechanical characterization of thin film amorphous semiconductors. 100 nm thick As2S3 and Ge-As-Se-Te glasses were thermally evaporated onto a bilayer microcantilever. The microcantilever was deflected and vibrated by electrothermal actuation. By monitoring deflection, amplitude and phase of the cantilever oscillation, multiple glass transition and melting points were identified; the effects of the variation of thermal expansion coefficients (CTE), reversible and irreversible heat capacities and Young?s modulus of the thin film samples were observed simultaneously. Hence the possibility of the integration of calorimetry, thermomechanical analysis (TMA) and dynamical mechanical thermal analysis (DMTA) in a single MEMS device was demonstrate
Nanomalzemelerin sentezi ve [Ru(bpy)3]2+ kompleksi ile birlikte sensör özelliklerinin araştırılması
In this study, optical properties of tris(2,2-bipyridyl)ruthenium (II) chloride ([Ru(bpy)3]2+), a ruthenium complex, together with various nanoparticles (TiO2 and core-shell TiO2@Ag nanoparticles) were investigated in the oxygen-permeable polymeric material. Plasticizer containing polymethylmethacrylate (PMMA) was shaped in form of thin film by applying the spin coating process and its optical properties and sensitivity towards oxygen were observed. It is known from previous studies that the [Ru(bpy)3]2+ complex exhibits extraordinary optical properties and high oxygen sensitivity when embedded in the above-mentioned matrix and used in combination with silver nanoparticles. In our thesis, the presented design is totally different from the earlier published literature. The porous and straight thin composite films were fabricated via the spin coating technique. Unlike the previous studies, the semiconductor TiO2 and core-shell TiO2@Ag nanoparticles were doped into these composite materials and the spectral properties of the prepared thin films were examined. Luminescence signal variations resulting from the application of oxygen sensor at 626 nm were recorded.
Çeşitli yöntemlerle magnetit nanotaneciklerin hazırlanması ve karakterizasyonu
Magnetite nanoparticles are used in various fields including iron-containing fluid, catalyst, pigments, magnetic recording media, medical diagnosis and treatment. Size of the particles and their morphology, electrical, optical and magnetic properties and limit their use. Synthesis methods determine the morphological homogeneity and size distribution of nanoparticles. Currently there are printing materials called toners that are imported for use in many printers of various brands and models. Iron-based inorganic minerals with different magnetic properties are used in these materials. The aim of this study is to prepare and characterize magnetite nanoparticles for use in printers and photocopiers. In this context, co-precipitation, thermal synthesis, sol-gel synthesis, reverse micelle synthesis, hydro-/solvo-thermal, sonochemical, microwave, and biosynthesis have been proposed. Magnetite nanoparticles were synthesized by co-precipitation and solvothermal/ hydrothermal methods. Stability of the nanoparticles stability is achieved by coating with oleic acid (OA), stearic acid (SA), sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), (3-aminopropyl)triethoxysilane (APTES), oleyl amine (OAm) and hexadecyltrimethoxysilane (HDTMS). Characterization of the prepared samples was performed by techniques such as XRD, FTIR, TGA, SEM, XPS and VSM.
Endüstri 4.0 kestirimci bakım süreçlerinde isteme özgü MEMS (mikro elektro-mekanik sistemler) tabanlı sensörlerin aksiyomatik tasarımla seçim problemi
Bu tez çalışmasının amacı endüstriyel alandaki makine v.b sistemlerin Endüstri 4.0 kestirimci bakım kapsamında ölçülmek istenen farklı parametrelerine özgü (ses, titreşim, akış v.b) olarak nanobilim alanındaki MEMS (Mikro Elektro-Mekanik Sistem) tabanlı sensörlerin aksiyomatik tasarım metodu uygun tasarımın bu metotla seçilmesinin araştırılmasıdır. Tez çalışması kapsamında ve devamında özel bir Ar-Ge merkezinde literatür taramasının ilerletilmesi, üniversite-sanayi işbirliği çalışmalar yapılması, bu çalışmalar ile uygulamalı bir projeye dönüştürülerek firmaların kestirimci bakım proseslerinde uygun MEMS tabanlı sensörün testlerinin yapılması hedeflenmektedir. MEMS tabanlı sensörlerin üretiminde kullanılan ve tasarımını/modellenmesini şekillendiren en uygun yöntemin (litografi v.b ) tespitinin yapılması için kavramsal araştırmalar yapılacaktır. Modelleme / desenleme sürecinden sonra, sensör tabanının/membranının boyutsal ve benzer parametreleri optimize edilecek ve aksiyomatik tasarım yöntemi ile en uygun tasarım seçilecektir. Son olarak MEMS tabanlı sensörler için yapılan seçimlerin nano ölçekteki NEMS (Nano Elektro-Mekanik Sistem) tabanlı sensörler için de uygun olup olmadığı değerlendirilecektir