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Öğe Degenerate magnetic structures and antiferromagnetic phase transitions in \gamma-Mn alloys(Turkish Journal of Physics, 1996) Bayrı, Ali; Atalay, Funda Ersoy; Gencer, HüseyinAbstract: Manganese alloy systems, which have been studied experimentally, show a host of antiferromagnetic phase transitions. Developing a linearized theory for the clas¬sical Heisenberg model, we can solve the local distortion of model of spins around an impurity in non-collinear antiferromagnet. Since the alloying removes the degeneracy in non-collinear magnets, this theory is useful. Looking at the case of ?-Mn alloys, especially Mn3Pt, we can predict the experimentally observed phase transitions caused by alloying.Öğe Different Plant Sporopollenin Exine Capsules and Their Multifunctional Usage(Amer Chemical Soc, 2022) Atalay, Funda Ersoy; Culum, Ayse Asiye; Kaya, Harun; Gokturk, Gunay; Yigit, EmelSporopollenin exine capsules (SECs) are highly resistant to heat and various acids and bases. They are also cheap, highly porous, eco-friendly polymer biomaterials with stable microencapsulation capacity. Due to their strong and uniquely shaped exine layers, they can allow growth on metal oxide materials, as a biotemplate for use in different applications. In this study, first, a single SEC extraction method was applied to three different pollens from Pinus, Fraxinus excelsior, and Tilia. Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, and thermogravimetric/differential thermal analysis (TGA/DTA) measurements both before and after the extraction process were performed to observe changes in surface area, morphology, porous structure, and degradation properties. The protein content and removal were analyzed by elemental and spectrophotometric analyses. Then, SECs were loaded by passive and centrifuge loading for drug delivery, and the loading capacities were analyzed by Fourier transform infrared spectroscopy and spectrophotometry. The method was successful in opening the pores and maintaining the structural integrity of SECs. It was determined that the morphology and porosity affected the encapsulation efficiency. According to the loading capacities, Tilia SECs were the most efficient SECs for both loading methods. In addition, three different SECs were hydrothermally coated with cobalt and then heat-treated to obtain a metal oxide structure. A CO3O4 supercapacitor electrode constructed using CO3O4-F. excelsior SEC powder had the best surface area parameters. The electrode showed a maximum specific capacity of 473 F/g for over 3000 continuous cycles of galvanostatic charge-discharge (GCD).Öğe Helical microtubules of nanostructured cobalt oxide for electrochemical energy storage applications(Biointerface Research Applied Chemistry, 2016) Atalay, Funda Ersoy; Kaya, Harun; Asma, Dilek; Bingol, AlperIn this study, Co3O4 nanostructured porous microtubes were prepared via chemical precipitation onto Aquaspirillum bengal bacteria in an aqueous solution. The morphological properties of the synthesized material were studied using a scanning electron microscopy (SEM). The diameter of the Co3O4 micro tubes is approximately 0.8 mu m, and the length is 4 mu m. The Brunauer-Emmett-Teller (BET) surface area was determined to be 87.07 m2/g. The nitrogen adsorption and desorption isotherm displayed properties associated with a typical type IV isotherm. The electrochemical properties of the produced material were studied using cyclic voltammetry (CV), long-term charge/discharge analysis and impedance spectroscopy (EIS).Öğe High-Performance Supercapacitor Electrode Based on NiFe Nanowire Networks/PEDOT:PSS(Elsevier, 2020) Atalay, Funda Ersoy; Sener, Melike; Kaya, HarunIn this work, the usage of electrochemically produced NiFe nanowires (NW) as an electrode active material for supercapacitors has been investigated. Different concentrations of NiFe NWs were dispersed on thin conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films by spin coating system. NiFe NW networks/PEDOT:PSS electrode was used as a positive electrode in the three-electrode cell. Electrochemical capacitive performance tests such as; electrochemical impedance spectroscopy, galvanostatic charge-discharge tests (GCD) and cyclic voltammetry (CV) were performed in 1 M Na2SO4 electrolyte. The CV curves of the designed electrodes have been found to be similar to the CV curves of the ideal supercapacitor and they have almost rectangular in shape. The specific capacitance of 2 mg NW mass loading was evaluated 332 F/g at a current density of 2 A/g from GCD measurements with excellent cyclability up to 5000 times. These good electrochemical performances arise from network structure of NiFe NW based electrode. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Influences of deposition time and pH on magnetic NiFe nanowires fabrication(Elsevier Science Sa, 2009) Atalay, Funda Ersoy; Kaya, Harun; Atalay, Selcuk; Tari, SueleymanIn this work, NiFe nanowires were grown into highly ordered porous anodic alumina oxide (AAO) templates by dc electrodeposition at various deposition times and pH values. During the deposition process some electrochemical bath parameters such as ion content, deposition voltage, and temperature of solution were kept constant. The morphological properties of the nanowire arrays were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the chemical composition was determined by examination of the energy dispersive X-ray (EDX) spectra, and the magnetic behavior of the arrays was determined by vibrating sample magnetometer (VSM). (C) 2008 Elsevier B.V. All rights reserved.Öğe Juglans Sporopollenin for High-Performance Supercapacitor Electrode Design(Amer Chemical Soc, 2020) Atalay, Funda Ersoy; Bingol, Alper; Kaya, Harun; Emre, Yildiz; Bas, Hatice Hande; Culum, Ayse AsiyeRecently, plant pollen has been used as a source of activated carbon to produce carbon-containing supercapacitor electrodes. However, in this study, pollen was used as a biotemplate with a completely different approach. As a biotemplate, pollen offers a wide range of varieties in terms of exterior, porosity, shape, and size. An electrode formed by the use of metal oxide grown on the pollen exine layer (sporopollenin microcapsules) as the active substance will inevitably exhibit good electrochemical capacitive properties. Juglans male flowers have been distinguished by dissection from anthers. Isolation of pollen grains from anthers was carried out using sieving from suitable sieves (45-200 mu m). Juglans sporopollenin exine microcapsules (SECs) were separated from the intine and protoplasm by acetolysis in combination with reflux. The solution containing SECs, metal ions, and Ni foam was put into a Teflon-lined hydrothermal container, and then, it was reacted at 120 degrees C for 15 h. The resulting precipitate, as well as the Ni foam, was heat-treated at 300 and 360 degrees C for 3 h in air. The raw pollen, chemically treated pollen, and cobalt-coated SEC (CoSEC) and CoSEC/Ni foam were characterized using scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, thermogravimetric analysis, and X-ray diffraction techniques. Two different types of supercapacitor electrode designs, with the use of exine microcapsules of Juglans sporopollenin, were performed for the first time. The maximum specific capacitance was up to 1691 F g(-1) at 5 A g(-1).Öğe Magnetic diffuse scattering in the frustrated square lattice(Turkish Journal of Physics, 1998) Bayrı, Ali; Atalay, Funda Ersoy; Gencer, HüseyinÖz: Başlık (İngilizce): Öz (İngilizce): Some of the first transition metal alloys show first order antiferromagnetic phase transition as a function of alloy concentration [1-5]. The antiferromagnetism of materials can be classified into three different class: type I, type II and type III. Although the neutron diffraction studies give information about the type of magnetism, they do not show the fluctuations of magnetic moment from the original direction. So in order to have some information about this fluctuations one must perform the magnetic diffuse scattering. Recently, we proposed that the square lattice may have a double-Q structure as well as single-Q [6]. We showed that the alloying may cause a first order antiferromagnetic phase transition. In order to show that this is the case we perform the magnetic diffuse scattering and give more evidences that the alloying play the dominant role in this phase transition.Öğe The role of clustering for antiferromagnetic phase transitions in \gamma-Mn alloys(Turkish Journal of Physics, 1996) Gencer, Hüseyin; Bayrı, Ali; Atalay, Funda ErsoyThe role of clustering for antiferromagnetic phase transitions in ?-Mn alloysÖğe Sol-gel synthesis of TiO2 on Co3O4-coated sporopollenin exine microcapsules (SECs) and photocatalytic performance of new semiconductor heterojunction material(Springer Heidelberg, 2022) Yilmaz, Hatice Caglar; Atalay, Funda Ersoy; Kaya, Harun; Erdemoglu, SemaIn this study, a new approach was developed to prepare mesoporous hybrid TiO2/Co3O4 coated on Juglans sporopollenin exine microcapsules (SECs). TiO2 was synthesized on Co3O4-coated SECs used as substrate, by sol-gel method. The obtained semiconductor/semiconductor hetero-junction hybrid materials were characterized with X-ray diffractometry (XRD), UV-Vis absorption spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), particle size distribution, specific surface area, and zeta potential measurements. Photocatalytic performances of hybrid materials were tested for Reactive Black 5 dye under both UV and visible light. Equilibrium pH of the solution containing 10 mg/L Reactive Black 5 dye and 0.1% wt/v TiO2/Co3O4 was around 4.7. After irradiation in the solar box, more than 98% of the Reactive Black 5 was photocatalytically degraded within 60 min.Öğe Synthesis of NiO Nanostructures Using Cladosporium cladosporioides Fungi for Energy Storage Applications(Sage Publications Ltd, 2016) Atalay, Funda Ersoy; Asma, Dilek; Kaya, Harun; Bingol, Alper; Yaya, PinarIn this work, we produced nickel oxide nanostructures that show high electrochemical capacitive behaviour, using fungus - one of the most common life forms in nature. Cladosporium cladosporioides fungi are particularly attractive biotemplates due to their tubular structures. The nanostructured porous microtubes were prepared by chemical precipitation onto fungi. The morphological properties of the biosynthesized NiO microtubes were studied by transmission electron microscope (TEM). The Brunauer-Emmett-Teller (BET) surface area was found to be 119.72 m(2) g(-1) with an average pore size distribution of 7.5 nm. A maximum capacitance value of 334 F g(-1) was observed at 0.8 A g(-1), and a capacitance retention of approximately 95% was obtained after 1000 cycles.
