Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Doping Effect on the Anode Material Capability of 2d Bn Nanosheets(01. Izmir Institute of Technology, 2024) Elmacı Irmak, Nuran; Özdemir, Mustafa Coşkun; Irmak, Nuran ElmacıIn this thesis, the potential of BNN surfaces doped with Al, Cl, Co, Fe, Ga, O, P, and S atoms as anode materials in K, Li, Mg, and Na ion batteries was investigated. Semi-empirical tight-binding combined with meta-dynamics methods and density functional theory were utilized to discover these properties. The effects of doping atoms on the electronic structure and geometry of BNN surfaces were also studied. Changes in the electronic structure and conductivity were reported by examining the HOMO-LUMO orbitals and the energy differences between these orbitals. Using previously reported experimental data and examining similar studies from the literature, the atoms to be doped were chosen. While vacancies at the sites of boron atoms in single-layer boron-nitride nanosheets were observed, vacancies formed by nitrogen atoms were not observed, indicating that boron vacancies are much more likely for the doping position. So that doping was performed on the boron atom. The level of quantum calculations used in this work was validated using experimental data. B3LYP/def2-SVP/D4/gCP level of theory is used for all calculations for BNN-nanosheets studied in this thesis. The bond lengths and the HOMO-LUMO energy difference were found to be nearly the same as the experimental data. The conductivity of the BNN surface was increased with the doping process. However, significant improvements are followed by doping of cobalt, iron, and sulfur atoms with 35%, 34%, and 26% alteration, respectively. For a suitable battery manufacture, the potential anode material should offer structures with high theoretical specific capacity, low anode electrode voltage, and minimal volume change between charged/discharged states. It was observed that none of the doped-BNN surfaces involved in this study were suitable for the use of anode material in magnesium ion batteries. On the other hand, they can be used as a negative electrode for potassium, lithium, and sodium batteries. Their capacity in lithium is better than Na and K batteries. Our results suggest that most of the doped BNN surface with ions studied in this thesis could be used as anode materials. However, none of them owns a better battery capacity than classic lithium batteries.Master Thesis Investigations on Nanoscale Wetting, Fluid Transport, and Droplet Evaporation at Nanostructured Surfaces by Molecular Dynamics Simulations(01. Izmir Institute of Technology, 2021) Şatıroğlu, Ezgi; Barışık, Murat; Özkol, ÜnverThere is a significant need to understand solid-liquid interactions at nanoscale to determine the fluid behavior in several revolutionary applications. Specifically, nanoscale surface wetting, nanoscale liquid transport, and nanoscale heat transfer are the most sought-after subjects in recent scientific and industrial applications. This thesis focuses on characterization and possible control of wetting, fluid flow, and heat transfer using nanoscale surface structures. First, wetting behavior on a nanostructured surface was studied to resolve contact angle hysteresis. The droplet was found stabilized at a metastable state with a contact angle significantly different from its equilibrium value due to contact line pinning from the surface asperities. The contact angle was found to increase linearly by increasing droplet size when the droplet is pinned. However, these pinning effects become negligible, and the contact angle reaches the equilibrium value of the corresponding surface when the surface structure size becomes negligible compared to droplet size. Second, fluid flow in nanostructured nanochannels was studied to determine the transport behavior. While the slip boundary condition on a smooth surface correlated with the wetting angle, transport in a nanostructured channel remained mostly independent from wetting condition of the corresponding surface structure. Lastly, droplet evaporation over nanopatterned surfaces was investigated. When the droplet temperature reached the Leidenfrost point, a sudden increase in the interface thermal resistance was observed, which significantly decreased the heat transfer to the droplet. Increasing the size of the surface structure pushed the Leidenfrost point to higher surface temperatures. Current results contribute to various disciplines in engineering and applied sciences.Master Thesis Production and Characterization of Emulsion Derived Porous Sioc+tio2 Submicron/Nanospheres(Izmir Institute of Technology, 2020) İçin, Öykü; Ahmetoğlu, Çekdar VakıfThe water resources are polluted because of the widespread use of dyes in the industry, resulting in a major ecological threat. Among the various water treatment techniques, adsorption and photocatalytic degradation methods are the most preferred owing to their easy applicability, low cost, and high efficiency. Silicon oxycarbide (SiOC), which is a type of polymer-derived ceramic, has the potential to be used in harsh environmental conditions thanks to its strong chemical stability and oxidation resistance, that being said it can also be used as a photocatalyst substrate. Titanium dioxide (TiO2) photocatalysts are extensively used for purification of contaminated waters. And also, TiO2 particles are synthesized with various material groups to investigate the adsorption and photocatalytic effect. In this thesis, initially, submicron/nano SiOC spheres were produced via an oil in water (o/w) emulsion technique by using parameters such as two types of preceramic polymer precursors (silicon oil and resin), mixing types (magnetically and ultrasonically), and different pyrolysis temperature (600-1200 oC). Upon the formation of submicron/nano SiOC spheres, selected samples were impregnated with a different molar of titanium oxide precursor solution (Titanium(IV) n-butoxide (TBT)) and calcined at 450 °C for 4 h. Various amounts of (0-5-10-20 wt.%) TiO2 containing submicron/nano SiOC spheres were produced and then characterized in depth by various techniques. Finally, the effects of pyrolysis temperatures and the amount of TiO2 were investigated in terms of adsorption and photocatalytic performance against aqueous cationic dye (methylene blue) (MB) solution. In the adsorption experiments, pure SiOC submicron/nanospheres (UM1200), pyrolyzed at 1200 oC, showed the best performance at the end of 24 h in the dark with 64% adsorption. In photocatalytic experiments, samples obtained by coating the SiOC substrate produced by pyrolysis at 600 oC with different amounts of TiO2 (UM600T5, UM600T10 and UM600T20) showed 79%, 80%, and 87% photodegradation efficiency.Master Thesis Preparation and Application of Subnano Ceramic Filtration Membranes for Organic Species Removal From Aqueous Streams(Izmir Institute of Technology, 2017) Yaltrık, Kaan; Çiftçioğlu, Muhsin; Çiftçioğlu, MuhsinThe purpose of this MSc work was to investigate the effects of neodymium/zirconium doping on the phase structure evolution of the selective titania nanofiltration (NF) membrane layers for the rejection of subnano sized organic compounds. A dilatometric study was carried out on unsupported membranes prepared from polymeric sols with different neodymium and zirconium levels. The development of functional abilities towards the design of the pore structure in the subnano range by controlling the nanostructural evolution of the selective NF layers was the fundamental purpose of this work. The neodymium doping level was varied in the 0.3-5.0% range and the zirconium mixing level was varied in the 0-100% range based on stable metal oxide molar compositions. Dilatometric characterization results have shown that dopant level effects the nanophase evolution and the densification behavior considerably. The dynamic light scattering results have shown that the polymeric species in the sol were predominantly 2-4 nm in size and had a very narrow size distribution. XRD analysis results indicated titania anatase crystallite sizes were reduced significantly with neodymium doping or zirconia mixing and the phase transformations were retarded by about 200°C. HR-TEM images of selected zirconia mixed or neodymium doped unsupported membrane powders also added new information to the XRD/dilatometry derived nanophase evolution results. The determination of the molecular weight cut-off values and pure water fluxes of the NF membranes which would be prepared by using these polymeric sols in the near future may generate valuable knowledge on the subnano separation abilities of these NF membranes.Master Thesis Quantum transport in nanostructured materials(Izmir Institute of Technology, 2017) Kurt, Gizem; Sevinçli, Haldun; Çakır, ÖzgürDue to the advances in the measurement and fabrication techniques at the nanoscale it is now possible to measure thermal transport across single molecule junctions[1], which makes it possible to consider nano-scale thermal devices. One of the building blocks for such thermal devices should be thermal switches. The aim of this study is to design a thermal switch, which is based on a single molecule junction and photoisomerism. We propose reversible photoisomerism as a key ingredient to build reversible thermal switches based on single molecule junctions. In this thesis, the thermal conductances of molecular junctions built by azobenzene and its derivatives are computed using density functional theory based tight binding method combined with atomistic Green’s functions. These molecules show photoisomeric behaviour by switching their three-dimensional structure when exposed to radiation. We investigate the effects of different linker groups as well as the details of the reservoirs. Carbon nanotubes are used as reservoirs, while generic reservoirs are also investigated to illuminate the effects of the reservoir details. We show that thermal conductance can be altered by switching the molecule from trans to cis configuration. The effect is robust under the change of the linkers that bind the molecules to the reservoirs and under the change of the particular molecular species.Master Thesis Growth and Characterization of Carbon Nanotubes by Thernal Chemical Vapor Deposition Method(Izmir Institute of Technology, 2008) Aksak, Meral; Selamet, YusufThis thesis work is focused on producing carbon nanotubes (CNTs) by methane gas thermal chemical vapor deposition method on very thin Cobalt, Iron, and Nickel catalyst thin films deposited onto SiO2/Si substrates by DC magnetron sputtering. This thesis is also devoted to understanding some parameters affecting the growth of CNTs; such as catalyst material, temperature, and catalyst layer thickness effects In this study, CNT growth was performed on directly Si substrates, which was observed that the growth was too difficult and requiring very high temperatures. Hence, very thin catalyst films were deposited on SiO2/Si substrates, and the CNT growth was observed. The temperature effect was also examined. When the growth temperature was increased, the average diameters of the CNTs were decreased up to a critical temperature, but after this point the average diameter of CNTs were increased. This effect was studied systematically by utilizing Fe and Co catalyst thin films and with the help of Raman spectroscopy and Scanning Electron Microscopy results.Catalyst thickness effect was also examined. For this aim, Ni catalyst thin films with three different thicknesses; 0.7 nm, 1.4 nm, and 6 nm, were utilized. It was observed that CNTs were grown well on 0.7 and 1.4 nm thick Ni films, while there was a little growth on 6 nm thick Ni film. The roughness analysis of 0.7 nm and 1.4 nm thick Ni films were also done. Some of as-grown CNTs were also examined by X-ray diffraction method, and the results were compared one another.Master Thesis Development of Carbon Black-Layered Clay/Epoxy Nanocomposites(Izmir Institute of Technology, 2008) Pekşen Özer, Bahar Başak; Tanoğlu, Metin; Tanoğlu, MetinIn this study, a novel epoxy nanocomposite with electrical conductivity and having improved mechanical and thermal properties was synthesized. Carbon black/ epoxy composites and carbon black-layered clay/epoxy nanocomposites were prepared by mixing via 3-roll mill. The first type of the composite was produced to determine the percolation threshold concentration (Vc). The second type with constant carbon black concentration, slightly over Vc, was synthesized to investigate the influence of clay content on the thermal, mechanical, electrical and structural properties of nanocomposites. Carbon black used in the study was extra conductive filler with 30 nm spherical particles. Layered clay was Na+ Montmorillonite treated with ditallow dimethlyamine to assure better intercalation within the epoxy resin. Vc value was determined to be 0.2 vol% and 0.25 vol% carbon black was added together with varying clay contents to the epoxy system to produce nanocomposites. Only the nanocomposites with 0.5 vol. % clay loading showed electrical conductivity. However, the composites with higher clay loadings showed insulating behaviour due to hindrance of carbon black network by clay layers. According to the XRD results, nanocomposites exhibited some extent of exfoliation. It was found that tensile modulus values of the epoxy increased;however flexural modulus values remained constant, with increasing clay content.Elastic modulus of neat epoxy (3.7 GPa) was increased about 28 % with 0.5 vol% clay addition. Thermomechanical analysis results revealed that the storage modulus, glass transition temperature and initial degradation temperature of epoxy was slightly enhanced due to clay loading.Master Thesis The Preparation Characterization and Sintering of Nanocrystalline Ceramics(01. Izmir Institute of Technology, 1999) Çağlar, Özlem; Çiftçioğlu, MuhsinNanocrystalline Titania was prepared by a chemical synthesis technique commonly known as sol-gel method. In the sol gel method, Titanium (IV) Isopropoxide was mixed with Isopropanol and Nitric Acid solution in predetermined ratios. A rapid hydrolysis reaction occurs between Titanium (IV) Isopropoxide and water in the Nitric Acid solution resulting in the formation of Titan oxide (Titania). The sols were clear sols and then gelled without any change in its clarity.Nanocrystalline Titania were tried to prepare by two different techniques in this work. The first technique involved the drying of the gel and subsequent sintering of the dried gel. A number of organic additives (oxalic acid, acetic acid, polyacrylic acid and stearic acid) were mixed into the sol before gelation in order to control drying (drying control chemical addives-DCCAs). Powders was prepared from sols and gels by several processes and a solid form was obtained by dry pressing and subsequently sintered in second technique. Oxalic acid was the most efficient DCCA among the others.The dried gels and powder compacts were sintered at 650, 700, 750, 800, and 850C. The sintering behaviors of them were examined. Relative densities of the dried gels were between 79-99% depending on the sintering temperature. The green body density of the pellets were varied between 41-52%. Their relative densities after sintering were varied between 55-83% depending on the sintering temperature. The pellets were pressed at different pressures to observe the pressure effect on the densification. Increase in pressure improve the densification behavior. The best route for the nanocrystalline powder preparation was the Route 4. This powder had smaller size of agglomerate most probably the agglomerates were broken during the ultrasonic radiation.The pore size analyses showed the pore structure of the gel. The pore size of the gels are about 35 nm. FTIR Spectra gave the crystal structure of the sols gels and powders. As a result, the sintering behavior of the dried gels is better than the powder compacts. The pellets can be densified to higher densities by appropriate forming technique. Although, the dried gels have significantly high densities, the shape and the weight of the gels can not be controlled.Master Thesis Development of Layered Silicate/Epoxy Nanocomposite(Izmir Institute of Technology, 2006) Kaya, Elçin Dilek; Tanoğlu, MetinLayered silicate/polymer nanocomposites are materials that display rather unique properties, even at low silicate content, by comparison with more conventional particulate-filled polymers. These nanocomposites exhibit improved mechanical, thermal, optical, gas permeability resistance and fire retardancy properties when compared with the pure polymer.In this study, layered silicate/polymer nanocomposites were prepared using Na+ cation containing montmorillonite (MMT) and epoxy resins. Silicate particles were treated with hexadecyltrimethylammonium chloride (HTAC) to obtain the complete homogenous dispersion of the nano plaques within the polymer matrix which forms the exfoliated microstructure. In this way, organophilic silicates (OMMT) were obtained.Modification of the silicate expands the silicate galleries (from 14 to 18 )that promote the formation of exfoliated composite structure. SEM results showed that nanocomposites with organically modified MMT exhibited better dispersion than those with MMT. It was found that the tensile and flexural modulus values are increased, whereas the fracture toughness is decreased with increasing silicate content. Thermal analysis results revealed that the glass transition temperature(Tg) of the neat epoxy resin (63.6oC) increases to 68.9 oC for the nanocomposites with 3 wt. % of OMMT. By incorporation of silicate particles, the dynamic mechanical properties of epoxy; including the storage and loss modulus and Tg are increased. Optical transmission values of the epoxy were affected by MMT and OMMT silicate incorporation. It was found that flame resistance at the polymer improved by the incorporation of MMT particles to the neat epoxy.Master Thesis Preparation and Physical Characterization of Clay/Epdm Nanocomposites(Izmir Institute of Technology, 2008) Karşal, Çiçek; Tanoğlu, MetinPolymer/clay nanocomposites have been extensively studied in recent years because they often exhibit improved properties different from their micro and macrocomposite counterparts. Addition of organophilic layered silicates to the polymer produces effective polymer nanocomposites by intercalation of macromolecules into the interlayer spaces. The performance of polymer/clay composites is not only related to the nature of the clay but also to the reinforcing mechanism of filler and the preparation conditions.In this study, the effects of mixing conditions and effect of aging on mechanical,physical and thermal properties of ethylene-propylene-diene rubber (EPDM)/Organo modified montmorillonite (OMMT) nanocomposites were studied at two different clay loadings 5 wt.% and 10 wt.%. EPDM/OMMT nanocomposites were prepared by melt blending method. The experimental results of X-ray diffraction (XRD) and scanning electron microscopy showed that the organically modified MMT existed in the form of an intercalated structure and that was exfoliated in EPDM matrix depending on the mixing conditions. XRD patterns showed that the interlayer distance of the organically modified clay was 30.9A, which was larger than those of the unmodified clay (14.6A).The mechanical evaluation of the nanocomposites was performed by tensile and tear testing. The mechanical tests showed that the properties of nanocomposites were significantly improved with addition of OMMT. The effects of the processing conditions were manifested in both the morphology and mechanical properties, which showed significant increase when optimized process conditions are applied. In addition, chemical test was performed on the nanocomposites to monitor the degradation of the mechanical properties. It was found that the reduction of the mechanical properties of nanocomposites after aging process is lower as compared to those of neat EPDM.