İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı Tez Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/420

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Design, synthesis, and characterization of n-type and ambipolar small molecules as air-stable and solution-processable semiconductors in ofets
(Abdullah Gül Üniversitesi, 2016) ÖZDEMİR, RESUL; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; ÖZDEMİR, RESUL
The design and development of novel ambipolar and n-channel semiconductors is very crucial to advance various optoelectronic technologies including organic fieldeffect transistors (OFETs) and complementary (CMOS) integrated circuits. Although numerous ambipolar and n-channel polymers have been realized to date, small molecules have been unable to provide high device performance in combination with ambient-stability and solution-processibility. In the first part of this thesis, two novel small molecules, 2OD-TTIFDK and 2ODTTIFDM, were designed, synthesized and characterized in order to achieve ultralow band-gap (1.21-1.65 eV) semiconductors with sufficiently balanced molecular energetics for ambipolarity. Bottom-gate/top-contact OFETs fabricated via solutionshearing of 2OD-TTIFDM yield perfectly ambient stable ambipolar devices with reasonably balanced electron and hole mobilities of 0.13 cm2 /V·s and 0.01 cm2 /V·s, respectively with Ion/Ioff ratios of ~103 -104 , and 2OD-TTIFDK-based OFETs exhibit ambipolarity under vacuum with highly balanced (µe/µh ~ 2) electron and hole mobilities of 0.02 cm2 /V·s and 0.01 cm2 /V·s, respectively with Ion/Ioff ratios of ~105 -106 . Furthermore, complementary-like inverter circuits were demonstrated with the current ambipolar semiconductors resulting in high voltage gains of up to 80. Our findings clearly indicate that ambient-stability of ambipolar semiconductors is a function of molecular orbital energetics without being directly related to bulk ?-backbone structure. To the best of our knowledge, considering the processing, charge-transport and inverter ii characteristics, the current semiconductors stand out among the best performing ambipolar small molecules in the OFET and CMOS-like circuit literature. Our results provide an efficient approach in designing ultralow band-gap ambipolar small molecules with good solution-processibility and ambient-stability for various optoelectronic technologies including CMOS-like integrated circuits. In the second part of this thesis, a new solution-processable and air-stable liquidcrystalline n-channel organic semiconductor (?,?-2OD-TIFDMT) was designed, synthesized, and characterized. The new semiconductor exhibits a low LUMO energy level (-4.19 eV) and a narrow optical band gap (1.35 eV). Typical pseudo focal-conic fan-shaped texture of a hexagonal columnar liquid crystalline (LC) phase was observed over a wide temperature range from melting point at 139 °C to isotropic transition point at 232 °C. The semiconductor thin-films prepared by spin-coating ?,?-2OD-TIFDMT shows the formation of large (~0.5-1 µm sizes) and highly crystalline plate-like grains with good interconnectivity. The molecules were found to adopt edge-on orientation on the dielectric surface resulting in favorable charge-transporting networks of ?-? stacking along the dielectric-semiconductor interface. Top-contact/bottom-gate organic fieldeffect transistors fabricated by using the spin-coated semiconductor films, which were annealed at a low temperature (Tannealing = 50 °C), have yielded good electron mobilities as high as 0.11 cm2 /V·s and high Ion/Ioff ratios of 107 -108 with excellent ambient stability. This indicates two orders of magnitude (100×) enhancement in OFET mobility when compared with a low-temperature annealed well-known semiconductor, ß-DDTIFDMT. Side-chain engineering in the new semiconductor structure offers great advantage for the D-A-D ?-core co-planarity while maintaining a good solubility in organic solvents, and leads to favorable optoelectronic and physicochemical characteristics for better OFET performance. Thermal annealing at LC phase results in significant deterioration in charge-transport with much lower (10,000×) electron mobility. These remarkable findings demonstrate that this new small molecule is a promising semiconductor material for the development of n-channel OFETs on flexible plastic substrates and LC-state annealing in columnar liquid crystals can be deteriorating for transistor-type charge transport.
Development of novel nanomaterials for display and catalysis applications
(Abdullah Gül Üniversitesi, 2016) TAHAOĞLU, DUYGU; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; TAHAOĞLU, DUYGU
Nanomaterials established a research presence due to their large variety and unique properties for many areas such as biotechnology, energy, fabrics, construction, food etc. Transparent conductors and catalysis applications are also two other important areas in which nanomaterial studies are carried out. For display applications, metal nanowires, especially silver and copper, draw too much attention as transparent conductors as an alternative to indium tin oxide (ITO), which is the most used material in this market, due to their high conductivity, low cost and availability for flexible device applications which are limitations for ITO. In catalysis applications, using nanomaterials are also important to provide two essential parameters: increasing the efficiency of reactions and lowering the cost. In this thesis, on the whole, we present the synthesis of silver and copper nanowires by optimizing some parameters for controlling the length and diameter of nanowires. For the surface passivation of nanowires, we offered some coating methods with noble metals such as gold, platinum and palladium. Also we investigated the catalytic activity of copper nanowires on dye wastewater treatment. In the first part of this study, effects of polyvinylpyrrolidone (PVP) polymer length and PVP:AgNO3 molar ratio on the efficiency of silver nanowire synthesis and nanowire size were investigated for polyol synthesis method. The results showed that reaction yield is highly depended on these parameters. Also, by using different coating methods such as direct addition or biphasic titration, and by using different noble metal precursors, galvanic exchange reactions on silver nanowire surfaces were studied. The results for coating showed that it is possible to replace silver and noble metal atoms through these methods. The next part of the thesis reports the copper nanowire synthesis ii by two different methods: hydrothermal and solution based synthesis. The copper nanowires showed different size properties for these two methods. In addition, the same coating processes were also performed for copper nanowires and the results are promising as silver nanowires. In the last part, catalytic performance of copper nanowires was studied on degradation reactions of three different organic dyes. Great differences between catalyzed and uncatalyzed reaction periods were observed for all dyes.
FABRICATION OF NANOCOMPOSITE MEMBRANES AND THEIR APPLICATIONS IN OILY WASTEWATER TREATMENT
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2017) SAKİ, Seda; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Industrial oily wastewaters are generated by various industries such as steel, food, textile, leather, petrochemical and metal milling and should be treated before discharging natural environment due to its serious environmental problems. With this view, membrane separation processes have promote a significant development of novel and green technology for oily wastewater treatment due to its clear advantages, for instance, ease in operation, efficient separation, low energy consumption and cost. Specially microfiltration (MF) and ultrafiltration (UF) membranes are playing a more prominent role in the oily wastewater treatments because of many advantages like as stable effluent quality, small area requirement, no chemicals addition, high chemical oxygen demand (COD) removal and low energy need. But the main drawback of membrane processes is the fouling problem. To overcome this problem, many researchers effort fabrication of high performance of membrane with higher hydrophilicity and antifouling properties. In this study, flat-sheet PSF/PEI nanocomposite membranes using Al2O3 and CaCO3 nanoparticles were prepared by phase inversion method. The effect of Al2O3 and CaCO3 nanoparticles were investigated on the structural properties and filtration performance of the nanocomposite membranes. Prepared membranes were characterized with scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), contact angle, porosity, water flux, thermogravimetric analysis (TGA), atomic force microscope ii (AFM), X-ray diffraction (XRD), BSA rejection, tensile strength, and viscosity measurements. Membrane permeability performance and antifouling properties towards oil water emulsion separation of these new generation nanocomposite membranes were evaluated for synthetic and real industrial oily wastewater. The results showed that there is a great potential to use these nanocomposite membranes for oily water treatment with higher permeability and antifouling capacity. All Al2O3 and CaCO3 nanocomposite membranes reached higher oil rejection ratios over 90%.
Fabrication of new generation membranes and their applications in fruit juice industry
(Abdullah Gül Üniversitesi, 2018) SEVERCAN, SOLMAZ ŞEBNEM; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; SEVERCAN, SOLMAZ ŞEBNEM
When membrane processes are compared to conventional processes, they have significant advantages for instance, providing decrease in operation time and cost with saving nutritious components and sensory parameters in food production plants. Especially, in fruit juice industry, UF membranes are utilized for clarification by eliminating big molecules like suspend proteins, fat and polysaccharides, which leads turbidity. Although, UF membranes have many advantages like its affordable cost, higher film forming ability, excellent mechanical properties, and superior chemical and thermal resistance, it has a major drawback leading the fouling of the membrane. To get rid of this problem, many researchers focused on the modification of membrane surface to both increase hydrophilicity and enhance antifouling characteristics. In this study, PSF/PEI (20wt%, 2wt%) UF membranes and PSF/PEI (17wt%, 2wt%) MF membranes were prepared with the addition of different concentrations of TiO2 and Al2O3 nanoparticles (0.01, 0.03, 0.05 wt %) using phase inversion method to alter the structural and morphological properties of membranes. Turbid apple and pomegranate juice samples supplied from Döhler Inc. (Karaman, Turkey) were clarified by using cross flow membrane filtration system and dead-end filtration system at 5.4 bar transmembrane pressure, respectively. Prepared nanocomposite membranes were characterized by using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), water-contact angle porosity and pure water flux. To investigate fouling resistance of nanocomposite membranes flux recovery ratio (FRR), flux decay ratio (DR), relative flux reduction (RFR) values were also calculated. In addition, ii clarified apple and pomegranate juice samples were characterized in terms of color, turbidity, total soluble solid, total antioxidant capacity (ABTS radical scavenging method and DPPH radical scavenging method) and total phenolic content. Total monomeric anthocyanin pigment content of pomegranate juice was also determined. The clarified juices obtained using new generation nanocomposite membranes were compared with the clarified product juice samples supplied from Döhler Inc. Membrane characterization and fruit juice characterization results demonstrated that fabricated new generation nanocomposite membranes were effective in apple and pomegranate juice clarification. Among these fabricated new generation nanocomposite membranes, the ones prepared with the addition of 0.01% of TiO2 UF membrane and prepared with the addition of 0.05% Al2O3 MF membrane exhibits superior performance in terms of clarification of apple juice and pomegranate juice, respectively.

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Browsing İleri Malzemeler ve Nanoteknoloji Ana Bilim Dalı Tez Koleksiyonu by Author "AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü"