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  • Öğe
    A DFT Study of Si Doped Graphene: Adsorption of Formaldehyde and Acetaldehyde
    (DergiPark, 2020) Akyavaşoğlu, Özge; Fellah, Mehmet Ferdi
    In this study, Si doped graphene sensor property for indoor volatile contaminants formaldehyde and acetaldehyde has been examined. The B3LYP hybrid method with 6-31G(d,p) basis set has been used for this purpose. The adsorption energy of formaldehyde and acetaldehyde have been found to be -24.5 and -33.3 kcal/mol, respectively. The characteristic C=O bond frequency has been decreased after adsorption of the molecules and the bond peaks frequencies have been decreased in both aldehydes. There was a charge transfer from adsorbent to formaldehyde oppositely from acetaldehyde to adsorbent.
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    A Density Functional Theory Study on Graphene Triple Doped with Ga, Ge, P, Si, and Al
    (MAIK NAUKA, 2022) Serinçay, Nazmiye; Fellah, Mehmet Ferdi
    The basic properties of graphene surfaces doped with Ga, Ge, P, Si, and Al were investigated using DFT (density functional theory). The structural, electrical, chemical and optical properties obtained by doping three elements onto the graphene structures modeled as a single layer were obtained in quantum chemical calculations with the WB97XD/6-31G(d,p) method. The HOMO-LUMO gap value, which expresses its chemical hardness, has decreased in the graphene structures doped with Ga-Ga-Ga, Ge-Ge-Ge, P-P-P, Si-Si-Si, and Al-Al-Al. Increased rigidity in doped graphene structures, increased movement of the system towards a more stable configuration, higher stability of the electronic structure, high chemical reactivity, high chemical potential, low electronegativity value, and high electrical conductivity. Increasing properties of element-doped graphene structures have predicted the structure's use in electronic devices such as transistors, energy storage devices, conductors, and sensors.
  • Öğe
    Hydrogen adsorption on Ni doped carbon nanocone
    (ELSEVIER SCIENCE SA, 2022) Köse, Ahmet; Yüksel, Numan; Fellah, Mehmet Ferdi
    Hydrogen adsorption was investigated on Ni doped carbon nanocone (Ni-CNC) 180 degrees C by Density Functional Theory (DFT). The WB97XD method was used with the 6-31G(d,p) and LanL2DZ basis sets. The electronegativity, HOMO and LUMO energies, chemical hardness, chemical potential, adsorption enthalpy and adsorption energy values have been calculated for hydrogen adsorption on Ni-CNC structure. The adsorption enthalpy value of hydrogen molecule was calculated as-27.8 kJ/mol. According to the storage capacity study for the Ni-CNC structure, it was found that this structure adsorbed eight hydrogen molecules and the hydrogen storage capacity was calculated to be similar to 4.3 wt%. After hydrogen adsorption, there was no significant decrease in HOMO-LUMO gap value. In addition, this situation indicates that the electrical conductivity of the Ni-CNC structure does not increase. These results show that the Ni-CNC structure cannot be used as a sensor for the hydrogen molecule, but it is a promising candidate material for hydrogen storage at room temperature.
  • Öğe
    Strategies to obtain tocopherols, phytosterols and squalene from deodorizer distillates and acid oils using supercritical fluids
    (Transworld Research Network, 2013) Adaşoğlu, Nalan; Gece, Ender Gökhan
    Recent Research Developments in Lipids, Strategies to obtain tocopherols, phytosterols and squalene from deodorizer distillates and acid oils using supercritical fluids
  • 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, Buğra
    In 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
    REMOVAL OF COPPER FROM INDUSTRIAL WASTEWATER USING SPENT COFFEE GROUNDS
    (Yıldız Teknik Üniversitesi, 2013) Adaşoğlu, Nalan; Bozkurt, Belgin; Salt, Inci
    In the literature, several studies have been reported on the sorption of metal ions from contaminated water using natural materials including bamboo dust, coconut shell, etc. which is modified with the chemicals or pyrolyzed, in batch mode studies or column systems. Indeed, in these possible scenarios containing waters formulated, sometimes, pre-treatments increase the cost. Therefore, in this study, adsorption studies have been performed by different kinds of spent coffee grounds with moist (60-65%) to determine the efficacy of Cu(II) removal from original industrial wastewater whose initial metal ions 2.11 g/L at pH 11.04 in bench-scale packed column. Results depending on experimental design have shown that spent coffee grounds rapidly remove copper from waste water to below detection levels. Consequently, heavy metal removal using original spent coffee grounds would be an effective method for the economic treatment of wastewater.
  • Öğe
    A Density Functional Theory study for adsorption and sensing of 5-Fluo-rouracil on Ni-doped boron nitride nanotube
    (Elsevier, 2021) Yüksel, Numan; Köse, Ahmet; Fellah, Mehmet Ferdi
    In this research, the use of Ni-doped (8,0) boron nitride nanotube (Ni-BNNT) as both a sensor and an adsorbent for 5-Fluorouracil (5-FU) molecule was investigated by Density Functional Theory (DFT) method. The B3LYP method with 6-31G(d,p) basis set have been utilized. Six different adsorption configurations have been studied theoretically. After 5-FU adsorption on Ni-BNNT, the adsorption energy values were calculated as negative values in all configurations. Adsorption energy (Delta E) value and adsorption enthalpy (Delta H) value reached 0.75 eV and -0.78 eV values, respectively. Moreover, Gibbs free energy changes were computed to be negative values in all configurations and thus it was determined that the process could occur spontaneously. Charge transfer occurred between all configurations of Ni-BNNT and the 5-FU molecule. The HOMO-LUMO gap decreased in the NiN-BNNT (Ni-doped instead of N) structure, while it increased in the Ni-B-BNNT (Ni-doped instead of B) structure. The Ni-BNNT structure assistances from a recovery time as a sensor for 5-FU drug molecule. Moreover, the workfunction change occurred somewhat in all configurations, but it was calculated that there was more change (16.22%) in the NiN-O1-BNNT configuration. In addition, solvent (water) effect was also examined. Consequently, Ni-doped (8,0) BNNT structure can be used as both a sensor and an adsorbent for 5-FU molecule at room temperature.
  • Öğe
    Usability, durability and regeneration of Ag/ZnO coated microreactor for photocatalytic degradation of methylene blue
    (Elsevier, 2021) Akman, Buğra; Aras, Ömür
    The 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.
  • Öğe
    Increasing biodiesel production yield in narrow channel tubular reactors
    (Elsevier, 2021) Baydır, Enver; Aras, Ömür
    The 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
    Processing and applications of ceramic microspheres
    (Elsevier, 2021) Geçim, Gözde; Kalemtaş, Ayşe
    This chapter is focused on processing techniques for dense, porous, and hollow ceramic microspheres and their applications. A large number of studies focused on modeling and observations from nature revealed that complex pore networks have many advantages. However, fabrication of the designed pore architecture remains a challenge, notably for the porous microspheres. Newly developed hierarchically porous microstructure design possibilities by optimizing the ceramic spheres’ processing conditions via numerous processing techniques, such as templating, solvothermal, sol-gel, spray-drying, and emulsion processes, are discussed in this chapter. The important characteristics, such as type, diameter, thickness, and surface area, of the microspheres developed by various processes are also given.
  • Öğe
    Retraction: Bimetallic platinum-rhodium nanocomposites for dimethylamine borane dehydrogenation: An experimental and density functional theory study (Catal. Sci. Technol. (2020) 10 (4624-4634) DOI: 10.1039/D0CY00641F)
    (Royal Society of Chemistry, 2021) Acidereli, Hilal; Fellah, Mehmet Ferdi
    Hilal Acidereli and Mehmet Ferdi Fellah hereby wholly retract this Catalysis Science & Technology article due to concerns with the reliability of the data in the published article. The high-resolution transmission electron micrograph inset in Fig. 1a, which represents PtRh@GO nanocomposites, is a duplicated, rotated and scaled version of high resolution transmission lectron micrograph insets in 41 other papers by the same author group all representing different nanoparticles or synthetic methods. The authors claim that this was a mistake and provided replacement data for consideration. However, an expert reviewed the authors’ response and concluded that it did not satisfactorily address the concerns, and that the replacement figure did not fully support the conclusions. The portions of the two XRD spectra in Fig. 2a between 30 and 55°, representing two different materials: Pt@GO and PtRh@GO, are the same. The authors provided replacement data for consideration. However, an expert reviewed the authors’ response and concluded that it did not satisfactorily address the concerns, and that the replacement figure did not fully support the conclusions. Given the significance of the concerns about the validity of the data, the findings presented in this paper are no longer reliable. Fatih Sen opposes this retraction. Oznur Alptekin, Betul Sen and Umran Ercetin were contacted but did not respond. Signed: Maria Southall, Executive Editor, Catalysis Science & Technology.
  • Öğe
    Removal of boron from industrial wastewater using PVP/PVDF blend membrane and GO/PVP/PVDF hybrid membrane by pervaporation
    (Springer, 2021) Özekmekçi, Mehtap; Ünlü, Derya; Çopur, Mehmet
    Removal of boron from water is a significant issue worldwide. Boron levels in waters containing high concentrations should be kept under control. Boron removal from the industrial wastewater released from Eti Mine Boron plants was investigated by using blend and hybrid membranes in a laboratory-scale pervaporation system. Polyvinylpyrrolidone/Polyvinylidene fluoride blend membrane and Graphene oxide/Polyvinylpyrrolidone/Polyvinylidene fluoride hybrid membranes were synthesized for this process. The membranes were characterized by using scanning electron microscopy, Fourier transform infrared, X-ray diffraction and contact angle measurements. Separation performance was evaluated in terms of flux, removal ratio of boron, and boron concentration in permeate within the membrane. Membranes showed higher separation performance in industrial wastewater. The highest boron removal was obtained as 99.86% with a flux of 0.755 kg/m2h when the 8 wt% graphene oxide loaded hybrid membrane was used. This study indicates that the Polyvinylpyrrolidone and Graphene oxide addition improved the membrane features and separation performances of the pervaporation process with improved hydrophilic membrane features can be preferred as an innovative water treatment method for the removal of boron from industrial wastewater. The obtained results show that pervaporation can be readily adapted to the removal of boron species by appropriate membrane selection.
  • Öğe
    Methyl-mercaptane adsorption and sensing on Fe-/Co-graphene structures: A DFT study
    (DergiPark, 2021) Yüksel, Numan; Köse, Ahmet; Fellah, Mehmet Ferdi
    In this research, the adsorption and detection abilities of Fe and Co doped graphene structures for methyl-mercaptan molecule were investigated by Density Functional Theory (DFT) method. B3LYP hybrid functional and LANL2DZ/6-31G(d, p) basis sets were used in the calculations. At the end of the adsorption processes, Fe and Co doped graphene structures were determined to be suitable adsorbents for the methyl-mercaptan molecule. In addition, charge transfer happened from the methyl-mercaptan molecule to the Fe and Co-doped graphene structures. The electronic sensor and the Φ-type sensor properties were also investigated and it was determined that Fe-graphene structure could be only used as an electronic sensor for methyl-mercaptan molecule at room temperature.
  • 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, Ömür
    In 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
    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, Yunus
    Nanocrystalline 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
    Gas Flow Hydrodynamics in Vortex Mixers: Flow Visualization and PIV Flow Field Characterization
    (American Chemical Society, 2021) Geçim, Gözde; Erkoç, Ertuğrul
    The gas flow hydrodynamics in a vortex mixer was investigated using flow visualization and particle image velocimetry (PIV) techniques for several Reynolds numbers ranging from Re = 20 to 280 and equal momentum of the jets. The flow regime transition of two methane gas streams coming from two tangential jets was analyzed by the detection of the critical Reynolds number of the flow. This critical point was determined from time-averaged and instantaneous flow images, velocity fluctuations, and hence turbulence intensity values of the vortex mixer. Results show that the flow gained the swirl motion at Re = 70 and the instabilities in the flow started at around Re = 230, where the gas flow hydrodynamics was diffusion controlled. Beyond Re = 230, the flow was unsteady and chaotic flow overruled the molecular diffusion and the ensemble mixing of the gases dependent on the convection was achieved starting from this point. This study sheds light on the gas flow hydrodynamics of a vortex mixer and points out the flow regime transitions.
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    An investigation of natural and modified diatomite performance for adsorption of basic Blue 41: Isotherm, kinetic, and thermodynamic studies
    (Desalination Publications, 2021) Kul A.R.; Aldemir A.; Koyuncu, Hülya
    In the present study, natural diatomite (ND) and Mn-modified diatomite (MD) were utilized for adsorption of Basic Blue 41 (BB 41) from aqueous solution at temperatures of 298, 308, and 318 K. Based on the results of isotherm studies, the Freundlich isotherm model is better than the Langmuir and Temkin models. Isotherm constants increase as the temperature increases, indicating that the removal process is favorable at higher temperatures. Adsorption kinetics for BB 41 on diatomite best fit the pseudo-second-order model which had kinetic constants that were higher than pseudo- first-order and intra-particle diffusion models. When the initial dye concentration rises from 10 to 80 mg L−1, adsorption capacity on ND and MD increase from 6.15 to 62.43 mg g−1 and 9.06 to 75.95 mg g−1 at 318 K, respectively. Gibbs free energy (ΔG°) values for BB 41 adsorption on ND and MD were determined as −11.224 and –15.586 kJ mol−1 at 318 K, respectively. Enthalpy (ΔH°) values for this removal process were calculated as 31.746 and 48.706 kJ mol−1, with entropy (ΔS°) values determined as 133.319 and 170.728 J mol−1 K−1 for ND and MD, respectively. Activation energy (EA) values were determined as 42.7 and 58.83 kJ mol−1 for BB 41 removal onto ND and MD adsorbents, respectively. Economic analysis of the preparation of Mn-modified diatomite was carried out. The results indicate that diatomite could be a good material compared to more costly adsorbents used for dye removal.
  • Öğe
    The reduced graphene oxide/WO3: Sensing properties for NO2 gas detection at room temperature
    (Elsevier Ltd, 2021) Fellah, Mehmet Ferdi
    The use of reduced graphene oxide/(WO3)3 as a sensor for NO2 gas was investigated by Density Functional Theory method and the results were compared with the experimental data. The charge transfer has happened between the adsorbed NO2 molecule and the reduced graphene oxide/(WO3)3 structure. The HOMO-LUMO gap of the rGO/(WO3)3 structure decreased after NO2 molecule adsorption. Based on this result, it has been revealed that the reduced graphene oxide/(WO3)3 structure can be both an electronic sensor and work function sensor. The reduced graphene oxide/(WO3)3 structure assistances from a recovery time as an sensor of NO2 molecule. Subsequently, the reduced graphene oxide/(WO3)3 structure have high potential to adsorb and detect the NO2 molecule at room-temperature. These findings have been supported by an experimental study where the reduced graphene oxide-WO3 film was used for NO2 gas sensing in literature and it has been reported that at room temperature it was a good sensing material for NO2 gas.
  • Öğe
    Biyoyakıt Bütanolün Metal Organik Kafes (MOF) İçeren Karışık Matrisli UiO-66/PVA Membranlar Kullanılarak Pervaporasyon Prosesi ile Dehidrasyonu
    (2020) Ünlü, Derya
    Bu çalışmada geleceğin önemli bir biyoyakıt maddesi olarak görülen bütanolün pervaporasyon ile dehidrasyonu hedeflenmiştir. Bu amaçla UiO-66 yüklü karma matris PVA membranlar sentezlenmiştir. Membranlar çözeltiden döküm ve solvent buharlaştırma tekniği kullanılarak hazırlanmıştır. Saf PVA membrana UiO-66 ilavesinin membranın kimyasal bağ yapısında meydana getirdiği değişim FTIR ile analiz edilmiştir. Membranların morfolojik yapıları ise SEM analizleri ile belirlenmiştir. Membranların besleme karışımındaki bileşenlere ilgisini belirlemek için solvent tutma deneyleri yapılarak su ve bütanol tutma kapasiteleri belirlenmiştir. UiO-66 miktarının, besleme su konsantrasyonunun ve operasyon sıcaklığının membranın ayırma performansına etkisi incelenmiştir. En iyi ayırma performansı ağırlıkça %0.5 UiO-66 yükleme oranı, ağırlıkça %5 besleme su konsantrasyonu ve 40oC operasyon sıcaklığında elde edilmiştir.
  • Öğe
    KINETICS OF THE ESTERIFICATION OF PROPIONIC ACID WITH ISOBUTYL ALCOHOL OVER AMBERLYST 36 AND AMBERLYST 70
    (2018) Çıtak, Alime; Hoşgün, Halit Levent
    The esterification of propionic acid with isobutyl alcohol has been studied in a batch reactor in the presence of Amberlyst 36 and Amberlyst 70 catalysts. Reaction parameters applied in this study are speed of agitation (500-1000 rpm), particle size of catalyst (400-600 µm, 600+ µm), temperature (318-348 K) and catalyst loading (4-12 g-dry resin/L). A pseudo-homogeneous kinetic model was derived and all thermodynamic and kinetic parameters were calculated. Forward reaction rate constant for Amberlyst 36 and Amberlyst 70 determined as follows: $ k1 = 160171 exp(-56689/RT) (L mol-1 min-1)$ $ k1 = 293314 exp(-57292/RT) (L mol-1 min-1)$ In a comparison of the two catalysts used in this study, experimental results showed that Amberlyst 70 is more effective than Amberlyst 36.