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Öğe Highly durable spray-coated superhydrophobic surface: Pre-anodizing and fatty acid chain length effect(KOREAN INSTITUTE CHEMICAL ENGINEERS, 2022) Aras, Ömür; Baydır, Enver; Akman, BuğraIn the study, aluminum plates were first anodized and then coated with ZnO by spray-pyrolysis method. By modification with long chain fatty acid, these surfaces demonstrate superior hydrophobicity and durability. After optimizing the anodizing time for each fatty acid, several runs were conducted by varying concentration and spray solution quantity. Comparison was made by optimizing the process parameters in which each acid showed maximum hydrophobicity. Anodized, spray coated and modified surfaces were characterized by FT-IR, XRD, SEM and topography analysis. The chemical and mechanical strength of the surfaces were explored under various extreme conditions. The highest contact angle of 164 degrees was obtained by coating 10 minutes anodized surface with 0.4 M and 15 ml ZnNO3 solution and modifying it with stearic acid. In the performed tests, it has been observed that this surface is much more durable than surfaces modified with other fatty acids.Öğe Increasing biodiesel production yield in narrow channel tubular reactors(Elsevier, 2021) Baydır, Enver; Aras, ÖmürThe purpose of this study is to augment the FAME yield by increasing the contact surface of the reactants that do not mix with each other in continuous biodiesel production. For this aim, many studies have been conducted in the literature and various reactor types have been used (tesla, omega, zigzag, etc.). Especially, the disadvantage of these intensive studies conducted on micro channels is undoubtedly pressure drops. In this study, narrow channel tubular reactors were preferred instead of micro channels, and t-type mixing cells were used to ensure well mixing. Mixing cells of different inner diameters (0.8, 1.2 and 1.5 mm) were adapted to reactors of various diameters (1, 1.5 and 3 mm). Then, the FAME yield was investigated at various catalyst amounts (0.5%, 0.75%, 1%) and residence times (1, 2, 2.5, 3 min). Additionally, it is observed that the percentage of FAME decreased as the residence time increased at smaller reactor diameters and higher catalyst amounts due to basically saponification effect. As a result, it has been shown that the high percentage of FAME, achievable in microchannels in short residence time, can also be achieved in narrow channel reactors with mixing cell assembly.Öğe Investigation of structural, spectral, optical and nonlinear optical properties of nanocrystal CdS: Electrodeposition and quantum mechanical studies(Elsevier GmbH, 2021) Erturk, Kadir; Isik, Seref; Aras, Ömür; Kaya, YunusNanocrystalline CdS semiconductor was synthesized by electrodeposition technique, and characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), and FTIR spectroscopic methods. XRD analysis result showed that it is a hexagonal crystal structure. SEM micrographs showed that the CdS nanocrystal is homogeneously distributed on the surface. The roughness of the CdS thin films was measured by AFM. The presence of band in the FTIR spectrum at 558 cm−1 corresponds to the stretching of CdS. CdS nanocrystals were modeled separately and calculated in the Gaussian program. Structural, spectroscopic, and nonlinear optical (NLO) properties were investigated using the DFT/Lanl2dz and semi-empirical/pm6 level. Besides, by making energy calculations, Homo, Lumo, band gap, and total state density (TDOS) were calculated. The experimental band gap was measured at 2.40 eV, while this calculated for hexagonal and cubic structure as 2.21 and 2.01 eV with semiemprical/pm6 model, 2.44 and 2.25 eV with DFT/lanl2dz level.These results support that CdS nanostructures are crystallized in hexagonal structure. With this study, the obtaining of nano structured CdS films by electrodeposition method, their structural, optical and surface properties were experimentally examined, supported by theoretical calculations, and additionally NLO properties were investigated. It has been determined that the nanocrystals obtained are suitable material for optoelectronic applications.Öğe Methanol steam reforming in a microchannel reactor coated with spray pyrolysis method for durable Cu/ZnO nanocatalyst(Elsevier B.V., 2021) Baydır, Enver; Aras, ÖmürIn this study, hydrogen production was carried out in microreactor by methanol steam reforming process. Electro etching method was used to obtain microchannels with different channel width and depth. Although there are different traditional methods for the catalyst to be used in hydrogen production, the spray pyrolysis method was chosen due to its many advantages. This method is a very effective and innovative when it is considered that microreactors are coated for hydrogen production. The system for spray pyrolysis coating was designed and setup. Thanks to this method, the coating of the reactor with nanocatalyst was carried out in a single step. Synthesis and coating with spray pyrolysis in a single step provided some advantages in terms of coating quality as well as saving time besides the durability tested by ultrasound experiments. In the last stage of the study, a methanol steam reforming system was setup to carry out the experiments in a catalyst-coated microreactor. Hydrogen production was carried out different steams / carbon ratios, different reactor temperatures, different feed rates. As a result, 94 % methanol conversion, 3% CO and 69 % H2 content were obtained for 275 °C reactor temperature, 1.8 steam/carbon (S/C) ratio and 0.02 cm3/min feed rate. In the literature, there are similar results in transformation and H2 selectivity. However, in this study, the synthesis and coating with catalyst spray pyrolysis in one step provided both financial and time advantages.Öğe Optimization of ultrasound-assisted extraction of phenolic compounds from grapefruit (Citrus paradisi Macf.) leaves via D-optimal design and artificial neural network design with categorical and quantitative variables(Wiley, 2018) Cigeroglu, Zeynep; Aras, Ömür; Pinto, Carlos A.; Bayramoglu, Mahmut; Kirbaslar, Sismail; Lorenzo, Jose M.BACKGROUND: The extraction of phenolic compounds from grapefruit leaves assisted by ultrasound-assisted extraction (UAE) was optimized using response surface methodology (RSM) by means of D-optimal experimental design and artificial neural network (ANN). For this purpose, five numerical factors were selected: ethanol concentration (0-50%), extraction time (15-60 min), extraction temperature (25-50 degrees C), solid:liquid ratio (50 - 100 gL(-1)) and calorimetric energy density of ultrasound (0.25-0.50 kW L-1), whereas ultrasound probe horn diameter (13 or 19 mm) was chosen as categorical factor. RESULTS: The optimized experimental conditions yielded by RSM were: 10.80% for ethanol concentration; 58.52 min for extraction time; 30.37 degrees C for extraction temperature; 52.33 g L-1 for solid:liquid ratio; 0.457 kW L-1 for ultrasonic power density, with thick probe type. Under these conditions total phenolics content was found to be 19.04 mg gallic acid equivalents g dried leaf. CONCLUSION: The same dataset was used to train multilayer feed-forward networks using different approaches via MATLAB, with ANN exhibiting superior performance to RSM (differences included categorical factor in one model and higher regression coefficients), while close values were obtained for the extraction variables under study, except for ethanol concentration and extraction time. (C) 2018 Society of Chemical IndustryÖğe Qualitative study on the effects of hydroxyl functionalized multiwall carbon nanotube and silica doped-epoxy composites(John Wiley and Sons Inc, 2022) Yaşaroğlu, İnci; Aras, Ömür; Kaya, YunusEpoxy resins have great potential for industrial applications because of their excellent properties such as good adhesion, durability, higher strength, and so forth. But, their high-viscosity limits industrial usage. Reducing the viscosity with suitable diluents provides an advantage on industrial scale processing, but this also causes a decrease in their chemical and mechanical properties. The production of epoxy-based composite materials provides good mechanical, heat, and solvent resistance properties. Therefore, determination of additives amount and dilution ratio for specific working area are important for these materials. In this context, this study first includes synthesis of bisphenol A-based epoxy resin and characterization with fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. Second, chemical, mechanical, thermal, and surface properties of the resin were investigated by varying the reactive/nonreactive diluents and additives. Multiwall carbon nanotube (MWCNT-modified with triton X-405 nonionic surfactant) and fumed silica as additives were used in this study. Mechanical and chemical tests were applied to 49 types of materials. In order to see the significance levels and synergistic effects of diluents on tensile strength, 3D graphs were obtained with the experimental and modeled data. ANOVA was also performed for significance levels of the diluents. After that, the effects of silica and carbon nanotube additive on tensile strength were investigated. As a result of the tensile test and TGA analysis of the pure epoxy, the ultimate tensile strength was measured as 59.07 MPa, Tg (°C), and Tm (°C) values were found as 175.5 and 304.0°C. These results increased for the nanocomposite material prepared with 2% fumed silica and 0.1% MWCNT (modified YAM) as 81.64 MPa, 192.2 and 333.3°C. It was also shown that the ultimate tensile strength, which decreased with dilution of pure epoxy, could be increased significantly with the additivesÖğe Usability, durability and regeneration of Ag/ZnO coated microreactor for photocatalytic degradation of methylene blue(Elsevier, 2021) Akman, Buğra; Aras, ÖmürThe microreactor, which was manufactured for the treatment of aqueous methylene blue (MB) solution, was coated with ZnO photocatalyst with different silver content using the spray pyrolysis method. Dye removal from water as a result of photocatalytic reaction at various residence times under UV-A irradiation was investigated. Here, the effect of morphological structures of ZnO-coated surfaces with and without silver on water treatment was observed. In addition, the effects of hydrogen peroxide at different rates on degradation and catalyst strength were investigated. As a result of experiments, 91% methylene blue degradation was obtained with 1% Ag doped ZnO coated microreactor for a residence time of 2.5 minutes. With the addition of 10% hydrogen peroxide, 96% of methylene blue removal was achieved. It was observed that if the photocatalyst coated reactors were operated for more than 40 hours, the removal efficiency decreased to approximately 62% and remained almost constant and again, returned to their previous performance when regenerated by hydrogen peroxide. In this study, for the first time, Ag/ZnO catalyst was coated on aluminum microreactor by spray pyrolysis method and the usability, durability and regeneration of this reactors were evaluated for the photocatalytic degradation of methylene blue under UV-A irradiation. The individual effects of UV radiation, H2O2 content and the catalyst on degradation were also investigated.
