Person: YUMUŞAK, GÖRKEM
Loading...
Email Address
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
YUMUŞAK
First Name
GÖRKEM
Name
9 results
Search Results
Now showing 1 - 9 of 9
Publication Open Access Production of reduced graphene oxide by using three different microorganisms and investigation of their cell interactions(2023-01-01) YUMUŞAK, GÖRKEM; Utkan G., YUMUŞAK G., Tunali B. C., Ozturk T., Turk M.Despite the huge and efficient functionalities of reduced graphene oxide (RGO) for bioengineering applications, the use of harsh chemicals and unfavorable techniques in their production remains a major challenge. Microbial production of reduced graphene oxide (RGO) using specific bacterial strains has gained interest as a sustainable and efficient method. The reduction of GO to RGO by selected bacterial strains was achieved through their enzymatic activities and resulted in the removal of oxygen functional groups from GO, leading to the formation of RGO with enhanced structural integrity. The use of microorganisms offers a sustainable approach, utilizing renewable carbon sources and mild reaction conditions. This study investigates the production of RGO using three different bacterial strains: Lactococcus lactis (L. Lactis), Lactobacillus plantarum (L. plantarum), and Escherichia coli (E. coli) and evaluates its toxicity for safe utilization. The aim is to assess the quality of the produced RGO and evaluate its toxicity for potential applications. Thus, this study focused on the microbial production of reduced graphene oxides well as the investigation of their cellular interactions. Graphite-derived graphene oxide was used as a starting material and microbially reduced GO products were characterized using the FTIR, Raman, XRD, TGA, and XPS methods to determine their physical and chemical properties. FTIR shows that the epoxy and some of the alkoxy and carboxyl functional groups were reduced by E. coli and L. lactis, whereas the alkoxy groups were mostly reduced by L. plantarum. The ID/IG ratio from Raman spectra was found as 2.41 for GO. A substantial decrease in the ratio as well as defects was observed as 1.26, 1.35, and 1.46 for ERGO, LLRGO, and LPRGO after microbial reduction. The XRD analysis also showed a significant reduction in the interlayer spacing of the GO from 0.89 to 0.34 nm for all the reduced graphene oxides. TGA results showed that reduction of GO with L. lactis provided more reduction than other bacteria and formed a structure closer to graphene. Similarly, analysis with XPS showed that L lactis provides the most effective reduction with a C/O ratio of 3.70. In the XPS results obtained with all bacteria, it was observed that the C/O ratio increased because of the microbial reduction. Toxicity evaluations were performed to assess the biocompatibility and safety of the produced RGO. Cell viability assays were conducted using DLD-1 and CHO cell lines to determine the potential cytotoxic effects of RGO produced by each bacterial strain. Additionally, apoptotic, and necrotic responses were examined to understand the cellular mechanisms affected by RGO exposure. The results indicated that all the RGOs have concentration-dependent cytotoxicity. A significant amount of cell viability of DLD-1 cells was observed for L. lactis reduced graphene oxide. However, the highest cell viability of CHO cells was observed for L. plantarum reduced graphene oxide. All reduced graphene oxides have low apoptotic and necrotic responses in both cell lines. These findings highlight the importance of considering the specific bacterial strain used in RGO production as it can influence the toxicity and cellular response of the resulting RGO. The toxicity and cellular response to the final RGO can be affected by the particular bacterial strain that is employed to produce it. This information will help to ensure that RGO is used safely in a variety of applications, including tissue engineering, drug delivery systems, and biosensors, where comprehension of its toxicity profile is essential.Publication Open Access Samarium and yttrium doping induced phase transitions and their effects on the structural, optical and electrical properties of Nd2Sn2O7 ceramics(IOP PUBLISHING LTD, 2020-01-15) YUMUŞAK, GÖRKEM; Saleh, Adli A.; Qasrawi, A. F.; Hamamera, Hanan Z.; Khanfar, Hazem K.; Yumusak, G.In this work, the effects of Sm+3 and Y+3 doping onto the structural, optical and electrical properties of Nd2Sn2O7 are investigated. An atomic content of 3.49% and 4.29% of Sm and Y, respectively, were sufficient to alter the physical properties of the Nd2Sn2O7. Particularly, the Y+3 ionic substitution decreased the lattice constant, narrows the energy band gap, changed the conductivity type from n- to p- type and increased the electrical conductivity by 73 times without changing the cubic nature of structure of the pyrochlore ceramics. On the other hand, Sm+3 ionic substitutions changed the cubic structure to hexagonal or trigonal and forced optical transitions in the infrared range of light. The energy band gap shrunk from 3.40 to 1.40 eV, the defect density is reduced and the electrical conductivity increased by 47 times via Sm doping. These doping agents' makes the neodymium stannate pyrochlore ceramics more appropriates for optoelectronic applications.Publication Metadata only Optimization of Sintering Parameters and Post Sintering Characterisation in Mullite-Zircon Ceramics(2023-05-25) YUMUŞAK, GÖRKEM; ARTIR, RECEP; Bal E., Yumuşak G., Artır R.In this study, with the help of the known effect of Fe2O3, which is a sintering aid additive for sintering, it is possible to synthesize products at temperatures much lower than 1500°C, which is the known sintering temperature in the phase diagram of the mullite-zircon system. In addition to the phase and microstructure analysis of the produced products as a result of the addition of sintering aid additive (Fe2O3) and reaction sintering process, mechanical characterizations were performed. The sintering aid additive (Fe2O3) was mixed into the Mullite-Zircon structure by adding 1 wt.%, 2 wt.% and 3 wt.%. 1% by weight of PAN was used as the binder. This mixture was formed into pellets before sintering under the selected pressing force of 2500 psi. These pellets were sintered at 1500°C, 1450°C, and 1400°C sintering temperatures, respectively, with a sintering time of 5 hours for each temperature. As a result of these processes, the effect of sintering temperature and the effect of the amount of sintering aid additives were examined by using characterization methods. It was aimed to determine the optimum parameters for this material, considering the important properties of ceramics such as porosity, hardness, density, and microstructure of the product to be produced with these additives and parameters. X-Ray Diffraction analyses were performed, and the phases formed as a result of the reaction were determined. Microstructure analyses were made for sintering temperatures of 1500°C, 1450°C, and 1400°C using an optical microscope. The optimum sintering temperature for the parameters used in this study and the amount by weight of the sintering aid additive to be used were selected considering variable factors in this study, and it was aimed to find the product with the best properties and the lowest cost.Publication Metadata only Gd and Tb doping effects on the physical properties of Nd2Sn2O7(ELSEVIER SCI LTD, 2018) YUMUŞAK, GÖRKEM; Saleh, Adli A.; Hamamera, Hanan Z.; Khanfar, Hazem K.; Qasrawi, A. F.; Yumusak, G.In the current study, we report the light doping effects of the gadolinium and the terbium on the structural, morphological, optical and electrical properties of Nd2Sn2O7 pyrochlore ceramics. The pyrochlore which is prepared by the conventional solid state reaction technique is analyzed by means of scanning electron microscopy, energy dispersive X-ray analyzer, X-ray diffraction, ultraviolet- visible light spectrophotometry and temperature dependent current -voltage characteristics techniques. It is found that even though the doping content of both metals is low (2%), they significantly alter the physical properties of the pyrochlore. Particularly, it is observed that, these two doping agents increases the lattice parameter and strain and reduces the crystallite size and dislocation density. Optically, the effect of Gd doping on shrinking the energy band gap value of the Nd(2)Sn(2)O(7 )pyrochlore ceramic is more pronounced than that of Tb. On the other hand, the electrical investigations have shown that while the Gd make the pyrochlore exhibit p-type conductivity through forming shallow acceptor levels, the Tb forces n-type conductivity by forming deep donor levels below the conduction band edge. Such acceptor and donor impurity levels increases the electrical conductivity of the Nd(2)Sn(2)O(7 )pyrochlore ceramics by 390 and 58 times, respectively.Publication Open Access Shielding effectiveness performance of polyaniline-NiFe2O4: Cu composites for sub-8 GHz applications(2023-06-01) YUMUŞAK, GÖRKEM; Şahin E. İ., Emek M., Ibrahim J. E. F. M., Yumuşak G., Kartal M.Herein, NiFe2O4 doped Cu was synthesized using a mixed-oxide method to investigate its potential for creating composites with high microwave shielding effectiveness. The compound NiFe2−xCuxO4 was synthesized with x values of 0.1, 0.3 and 0.5, respectively. After sintering at 1250°C for 4h, single-phase Ni ferrite was formed. To analyze the phase composition and the structure of the synthesized compound, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were employed. The study\"s findings showed that NiFe2−xCuxO4 did not exhibit a second phase. To create composites with high microwave shielding effectiveness, polyaniline-NiFe2O4:Cu composites were fabricated using a hot-pressing technique, with compositions of NiFe1.9Cu0.1O3.95, NiFe1.7Cu0.3O3.85 and NiFe1.5Cu0.5O3.75 with the aniline, The weight ratios of Cu-added nickel ferrite and aniline were changed from 1:1 to 1:3, and epoxy resin was used. Using a two-port vector network analyzer, the polyaniline-NiFe2O4:Cu composites’ microwave shielding effectiveness performance was examined in the range between 0 and 8GHz. The study found that the shielding effect of the composites could be easily modified by changing the amount of polyaniline present in the specimens for the appropriate frequency bands. At 6.82GHz, using a sample with a thickness of 2.0mm, a minimum shielding effect performance of − 29.74dB was achieved. Overall, the results of this study demonstrate the potential of polyaniline-NiFe2O4:Cu composites as effective microwave shielding materials.Publication Metadata only Fabrication and characterization of anodic films on 304 stainless steel(2022-11-19) SARIOĞLU, CEVAT; YUMUŞAK, GÖRKEM; Ağırlar N., Bağcı N. C., Arkalı E., SARIOĞLU C., YUMUŞAK G.Publication Open Access The effect of pre-deposited titanium-based PVD metallic thin films on the nitrogen diffusion efficiency and wear behaviour of nitrided Ti alloys(ELSEVIER SCIENCE SA, 2020-07) YUMUŞAK, GÖRKEM; Yumusak, G.; Leyland, A.; Matthews, A.Low-temperature Triode Plasma Nitriding (TPN) has been reported to increase the load-bearing capacity of titanium alloys without compromising either core strength or fatigue resistance. It is known also that the effective adhesion between PVD hard coatings and titanium alloy substrates can be improved significantly following substrate diffusion pre-treatment. In TPN treatment the diffusion of the nitrogen can be achieved more efficiently (than conventional nitriding techniques) at a comparatively low substrate temperature and after relatively short treatment times. Moreover, there is evidence to suggest that the effectiveness of the triode-plasma diffusion treatment can be further increased by depositing a suitable thin PVD metallic layer on to the titanium alloy substrate before plasma nitriding treatment, to beneficially modify the diffusion kinetics. In this paper, both hcp-alpha and bcc-beta titanium coatings (the latter stabilised by the addition of Nb) are applied to (alpha + beta) Ti-6Al-4V and (beta) Ti-4Al-10V-22Mo substrate materials; the effects of a Ti and beta Ti-Nb PVD pre-coating on the diffusion treatment efficiency (and nitride phase development) and the wear behaviour of each of the Ti alloy substrates after TPN treatment at 700 degrees C is evaluated.Publication Open Access Physical properties of neodymium tin oxide pyrochlore ceramics(DE GRUYTER POLAND SP ZOO, 2017-10-20) YUMUŞAK, GÖRKEM; Saleh, Adli A.; Qasrawi, A. F.; Yumusak, G.; Mergen, A.In this work, physical properties of neodymium tin oxide pyrochlore ceramics prepared by solid state reaction technique are investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet-visible light (UV-Vis) spectrophotometry and temperature dependent electrical resistivity measurements. The pyrochlore is observed to have a cubic FCC crystal lattice with lattice parameter of 10.578 angstrom. The planes of the cubic cell are best oriented in the [2 2 2] direction. From the X-ray, the UV-Vis spectrophotometry and the electrical resistivity data analysis, the grain size, strain, dislocation density, optical and thermal energy band gaps, localized energy band tail states and resistivity activation energies are determined and discussed. The pyrochlore is observed to have an optical energy band gap of similar to 3.40 eV. This value corresponds to 365 nm UV light spectra which nominates the neodymium tin oxide pyrochlore ceramics for the use as UV sensors.Publication Open Access A microabrasion wear study of nitrided α-Ti and β-TiNb PVD metallic thin films, pre-deposited onto titanium alloy substrates(2022-07-01) YUMUŞAK, GÖRKEM; YUMUŞAK G., Leyland A., Matthews A.© 2022 Elsevier B.V.In this paper, we study the structure, mechanical properties and abrasion resistance of two triode-plasma nitrided (TPN) titanium alloys, pre-coated with metallic α-Ti or β-TiNb layers deposited by physical vapour deposition (PVD). The chosen alloys were Ti-6Al-4V and Ti-4Al-10V-22Mo, which are predominantly alpha- and beta-phased, respectively – each presenting different challenges, in terms of their nitriding response. Although duplex nitriding + PVD coating is now quite widely employed on steels (and increasingly on titanium alloys) to improve load-bearing capacity and wear resistance, the use of PVD coatings prior to diffusion treatment to control surface roughness – and, in the case of Ti-alloys particularly, to optimise their ‘challenging’ diffusion kinetics has received little or no attention so far. The TPN process enables diffusion treatments to be carried out at 700 °C – which is lower than the beta-transus temperature of Ti (and of most Ti alloys). Optical microscopy, scanning electron microscopy, atomic force microscopy, X-ray diffraction, nanoindentation, and surface profilometry were used to characterize the nitrided and coated/nitrided samples. It was found that the nitrogen concentration and surface hardness for all samples was significantly increased, and that the surface roughness values significantly increased for uncoated Ti alloy substrates after TPN treatment – due to intense, grain orientation-dependent plasma etching effects. However, our novel approach of PVD pre-deposition of a nanostructured metallic coating prior to nitriding reduces surface roughening effects quite dramatically. The micro-abrasion resistance of Ti- and TiNb-coated Ti-6Al-4V substrates was significantly enhanced after nitriding treatment; on the other hand, similar improvements were not found for the metastable-beta Ti-4Al-10V-22Mo substrates – due to the different nitriding behaviour of the pre-deposited PVD surface layers. The \"sputter removal\" rates for the metallic coatings were high, but all coatings survived in part until the end of the nitriding process.