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Öğe A comparative study for lipase immobilization onto alginate based composite electrospun nanofibers with effective and enhanced stability(Elsevier, 2017) Dogac, Yasemin Ispirli; Deveci, Ilyas; Mercimek, Bedrettin; Teke, MustafaIn this study, lipase was successfully immobilized on polyvinyl alcohol/alginate and polyethylene oxide/alginate nanofibers that were prepared by electrospinning. Results showed that nanofibers (especially polyvinyl alcohol/alginate) enhanced the stability properties of lipase. When the free lipase lost its all activity after 40-60 min at high temperatures, both lipase immobilized nanofibers kept almost 65-70% activity at the same time. The lipase immobilized poly vinyl alcohol/alginate and polyethylene oxide/alginate nanofibers protected approximately all of their activities until pH 9. Lipase immobilized polyvinyl alcohol/alginate and polyethylene oxide/alginate nanofibers maintained 60% of their activities after 14 and 7 reuses, respectively. The morphology of nanofibers was characterized by Scanning Electron Microscope, Fourier Transform Infrared Spectroscopy and Thermal Gravimetric Analyzer. As a result, this nanofiber production method, electrospinning, is simple, versatile and economical for preparing appropriate carrier to immobilize the enzymes. (C) 2016 Elsevier B.V. All rights reserved.Öğe A Comparative Study of Electrochemical Behaviors of 1-nitroso-2-naphthol on Glassy Carbon and Platinum Electrode Surfaces by Cyclic Voltammetry(Univ Tehran, Fac Chemistry, Center Excellence Electrochemistry, 2012) Mulazimoglu, Aysen Demir; Yilmaz, Ecir; Mercimek, Bedrettin; Mulazimoglu, Ibrahim EnderIn the present work, electrochemical and spectroelectrochemical behaviors of 1-nitroso-2-naphthol has been studied by cyclic voltammetry and electrochemical impedance spectroscopy techniques in non-aqueous media. Cyclic voltammetric studies of 1-nitroso-2-naphthol in acetonitrile containing 100 mM tetrabutylammonium tetrafluoroborate on glassy carbon and platinum electrodes were performed between 0.0 mV and +2600 mV potential range at 100 mV s(-1) scan rate with 10 cycles. Anodic peaks were observed at 475.3 mV, 958.9 mV, 1395 mV and 2103 mV for 1-nitroso-2-naphthol on the glassy carbon electrode surface vs. Ag/Ag+ reference electrode. The surface characterizations were carried out by using cyclic voltammetry and electrochemical impedance spectroscopy techniques in both aqueous and non-aqueous media. Electrochemical behaviors of 1-nitroso-2-naphthol on glassy carbon and platinum electrode surfaces were compared.Öğe Determination of photovoltaic parameters of CIGS hetero junction solar cells produced by PLD technique, using SCAPS simulation program(Pergamon-Elsevier Science Ltd, 2021) Gezgin, Serap Yigit; Houimi, Amina; Gundogdu, Yasemin; Mercimek, Bedrettin; Kilic, Hamdi SukurIn this study, CIGS ultrathin films of 52 nm, 89 nm, 183 nm and 244 nm thicknesses were grown on a n-Si substrate using PLD technique, then Ag/CIGS/Si/Al hetero-junction solar cells were formed by producing front finger and back contact. While the thickness of CIGS ultrathin film is increased, their grain sizes are also increased, crystal structures are developed and more light is absorbed within the thin film. The straight characteristics of hetero-junctions have been improved while the thicknesses of CIGS ultrathin film is decreased according to J-V characteristics of the hetero-junctions in the darkness. In addition, depending on CIGS ultrathin film thickness, the photovoltaic behavior of CIGS/Si hetero junction solar cells has been studied and interpreted in detail in this article. It can be concluded that CIGS/Si hetero-junction solar cell device produced based on CIGS ultrathin film of 183 nm thickness shows the highest short circuit current density and power conversion efficiency values among other thicknesses, with respect to J-V curve under the illumination (AM 1.5 solar radiation in 80 mW/cm2). Using SCAPS 1-D program, we have been able to successfully simulate CIGS/Si hetero-junction of 183 nm thickness.Öğe The Effect of CZTS Ultrathin Film Thickness on the Electrical Characteristic of CZTS/Si Heterojunction Solar Cells in the Darkness and under the Illumination Conditions(Springer, 2021) Gezgin, Serap Yigit; Houimi, Amina; Mercimek, Bedrettin; Kilic, Hamdi SukurIn this study, Ag/CZTS/Si/Al heterojunction solar cells were produced depending on some parameters of CZTS ultrathin active film layers grown on a n-Si wafer by PLD technique. CZTS ultrathin films have been produced as a function of the number of laser pulses and then annealed in a tube oven as a function of sulfurization temperature. The crystal structure, the optical and morphological properties of grown&annealed CZTS ultrathin films were examined by XRD, UV-vis spectra, AFM, respectively. The electrical characteristics of CZTS heterojunction solar cell in the darkness, which were investigated by the conventional J-V Method, Cheung Cheung Method and Norde Method. As the thickness of CZTS ultrathin films increased, the forward current of CZTS heterojunctions increased and their ideality factor, serial resistance and barrier height decreased. Also, the efficiency of Ag/CZTS/Si/Al heterojunction solar cells have been examined and characterised as a function of CZTS ultrathin film thickness under the illumination conditions. J-V curves of CZTS heterojunction solar cells were determined under AM 1.5 solar radiation in 80 MW/cm(2), all CZTS heterojunction solar cells have exhibited the photovoltaic behaviour. J(sc), V-oc, FF, eta parameters of Ag/CZTS/Si/Al heterojunction solar cells were measured, interpreted and compared with each other.Öğe Effect of Li Doping on Cu2SnS3/n-Si Heterojunction Solar Cells: Experiments and Simulation(Wiley-V C H Verlag Gmbh, 2023) Houimi, Amina; Gezgin, Serap Yigit; Mercimek, Bedrettin; Kilic, Hamdi SukurCu2SnS3 (CTS) semiconductor material owns very interesting absorbing properties that allow it to be effectively utilized in many thin-film-based heterojunction solar cells. In this work, using the ball milling method, a mixture of pure elemental powders is used to synthesize CTS material. Homemade undoped and Li-doped target pellets are used to form CTS-doped and CTS-undoped thin films. The crystallinity investigation of synthesized targets and thin films confirms the formation of CTS tetragonal phase. Compositional, morphologic, and optic studies are also made to examine the effect of Li atom incorporation on different properties of CTS thin films. These CTS thin films are also incorporated into heterojunction solar cells (Al/n-Si/CTS/Ag and Al/n-Si/Li0.03CTS/Ag). In addition, J-V characteristics of both CTS and Li0.03CTS solar cells are demonstrated and discussed in details. The effect of CTS thin films' thickness on the performance is studied using Solar Cell Capacitance Simulator (SCAPS-1D) program. The results of the calculation are discussed in details and compared with the experimental results. An increase in efficiency is achieved in solar cells based on Li-doped CTS thin films, and it is discussed in detail along with SCAPS-1D simulation that is carried out depending on the thickness of CTS thin films.Öğe The electrical properties of ZnO/Si heterojunction diode depending on thin film thickness(Korean Physical Soc, 2022) Akin, Ummuhan; Houimi, Amina; Gezgin, Bahri; Gundogdu, Yasemin; Kilic, Sumeyye; Mercimek, Bedrettin; Berber, AdnanIn this work, ZnO thin films have been produced on p-Si wafer depending on number of laser pulses applied using pulse laser deposition (PLD) technique at room temperature conditions. Three different thicknesses of ZnO thin films (ZnO1, ZnO2 and ZnO3) have been produced by applying 18,000, 36,000 and 54,000 laser pulses and thicknesses of these produced three thin films have been measured to be 41 nm, 70 nm, 197 nm, respectively. It is observed in this work that while thicknesses of ZnO thin films increases, crystal structure of thin films develops, their grain size increase while their band gaps decrease. Ag/ZnO/Si/Au heterojunction diodes have been produced based on ZnO1, ZnO2 and ZnO3 thin films. After that, effect of thickness of thin film on electrical properties of diodes produced depending on number of laser pulses has been analyzed in detail. I-V characteristics of ZnO/Si heterojunction diodes produced have also been measured in darkness environment and under illumination conditions (AM 1.5 solar radiation of 80 mW/cm(2)) and results obtained have been interpreted and a conclusion has been made in this work. Furthermore, ideality factors, barrier heights and serial resistivities of these diodes have been calculated using conventional thermionic emission theory, Norde and Cheung-Cheung methods and then results obtained from analytical methods have been interpreted in detail in the present article. ZnO heterojunction diodes have exhibited photovoltaic properties under illumination conditions. It has been observed that as thickness of ZnO thin film is increased, J(sc) and eta values of the hetero junction diodes are increased. ZnO-3A hetero junction diode has exhibited the most improved photovoltaic performance. We have also theoretically investigated photo-electric properties of ZnO-3A heterojunction diode using SCAPS-1D packed software. The resulted J-V characteristics have been found very similar to measured counterparts.Öğe Electrochemical Grafting by Reduction of 4-Methylaminobenzenediazonium Salt at GC, Au and Pt Electrode: Investigation of Sensitivity Against Phenol by Cyclic Voltammetry(Univ Tehran, Fac Chemistry, Center Excellence Electrochemistry, 2012) Mulazimoglu, Aysen Demir; Mulazimoglu, Ibrahim Ender; Mercimek, BedrettinThe aim of this study is to modify a glassy cabon, gold and platinum electrode with 4-methylaminobenzenediazonium salt (MABDAS) to evaluate the possible application on the detection of phenol by cyclic voltammetry (CV). Diazonium salt was reduced electrochemically and covalently electro-grafted onto GC, Au and Pt electrodes surface to form modified electrodes in non-aqueous media. The electrode surfaces were modified with MABDAS in acetonitrile (CH3CN). MAB modified GC (MAB/GC) electrode was used for the phenol determination in aqueous media. The effect of pH on the electrochemical behavior of the modified GC electrode was investigated for the phenol detection.Öğe A novel highly sensitive carbon-based HMPD/GC sensor electrode: copper ions analysis in flour and water samples(Desalination Publ, 2018) Durmus, Nagihan; Yilmaz, Ecir; Mulazimoglu, Aysen Demir; Mercimek, Bedrettin; Cukurovali, Alaaddin; Yilmaz, Ibrahim; Solak, Ali OsmanIn this research, (Z)-2-(2-(hydroxyimino)-2-(3-methyl-3-phenylcyclobutyl) ethyl)-3a,7a-dihy-dro-1H-isoindole-1,3(2H)-dione, HMPD molecule has been grafted to the glassy carbon (GC) electrode surface. The HMPD-modified GC electrode has been originally developed and it used for the quantitative determination of Cu(II) in flour and water samples. The modification steps have been performed using cyclic voltammetry (CV). CV, electrochemical impedance spectroscopy and scanning electron microscopy have been employed for the characterization processes. Cu(II) standard solutions changing from 1.0 x 10(-9) to 1.0 x 10(-3) M have been prepared and the corresponding peak currents have been measured. From the obtained data calibration equation has been calculated I-p = -1.555C(cu) + 15.86 which is having a 0.9974 correlation coefficient. 10.0 mL of flour and water samples have been mixed with 10.0 mL Britton-Robinson (BR) buffer solution (pH = 5.00) and HMPD/GC sensor electrode has been kept in these mixed solutions for 90 min. Differential pulse voltammetric (DPV) technique has been applied for the measurement of the peak currents. After the application of the developed sensor electrode for Cu(II) detection in flour and water samples, Cu(II) ion concentrations have been calculated from the obtained peak current values, 1.97 and 2.46 mu A. The Cu(II) ion concentrations have been calculated as 1.17 x 10(-9) and 2.41 x 10(-9) M, respectively.Öğe Numerical analysis of CZTS/n-Si solar cells using SCAPS-1D. A comparative study between experimental and calculated outputs(Elsevier, 2021) Houimi, Amina; Gezgin, Serap Yigit; Mercimek, Bedrettin; Kilic, Hamdi SukurCZTS (Cu2ZnSnS4) is a p-type semiconductor material which has been intensively used as an absorbing layer for thin film solar cells. Using pulsed laser ablation + deposition technique, we have been able to successfully form a CZTS/n-Si heterojunction solar cells with an optimum thickness of 210 nm of CZTS thin film. Different characteristics (optic, crystal and morphologic) of CZTS thin films have been investigated according to the thickness of CZTS thin film. We have accomplished a simulation work based on CZTS/c-Si hetero junction solar cells using SCAPS-1D. Into this model, experimental data including band gap, thickness and absorption coefficient have been introduced. The change of hole carrier's density in CZTS thin film, interface defect density in CZTS/n-Si hetero junction and device temperature have been found to be very influential on J-V characteristics of a CZTS (210 nm)/c-Si solar cell. SCAPS-1D model has also been introduced for the other three different CZTS thin films thicknesses and the results obtained from both SCAPS-1D program and experimental measurements have been found to be very close to each other.Öğe Performance of SiO2/Ag Core/Shell particles in sonocatalalytic degradation of Rhodamine B(Elsevier Science Bv, 2019) Deveci, Ilyas; Mercimek, BedrettinIn this study, SiO2/Ag Core/Shell nanoparticles was prepared and sonocatalytic activity of prepared catalyst was investigated by using Rhodamine B as model contaminant, at 35 kHz using ultrasonic power of 160 W within 90 min. The change in efficiency in the sonocatalytic degradation of Rhodamine B catalyzed by SiO2/Ag Core/Shell nanoparticles with respect to the initial concentration of dye, catalyst amount and temperature were firstly investigated. Optimal conditions were found as follows: catalyst amount = 15 mg/L, Temperature = 25 degrees C and initial concentration of dye = 10 ppm. Influence factors such as pH of solution, O-2 saturation of solution and the concentration of H2O2 added to the solution, on degradation efficiency in presence of catalyst, were investigated. SiO2/Ag Core/Shell nanoparticles showed higher sonocatalytic activity at pH = 7 with respect to acidic and alkaline conditions. Degradation efficiency was reached up to 67% in experiments which air pumped (0.6 L/min) through the solution with in 90 min. It was observed that the dye removal increased via increase while H2O2 concentration lower than 10 mM. Higher concentration of H2O2 than the optimal concentration had adverse effect on degradation efficiency. Our results showed that the SiO2/Ag Core/Shell nanoparticles were active catalyst for sonocatalytic degradation of dyes. Reusability of the catalyst was investigated.Öğe Synthesis and Characterization of Chitosan/TiO2 Composite Beads for Improving Stability of Porcine Pancreatic Lipase(Humana Press Inc, 2015) Deveci, Ilyas; Dogac, Yasemin Ispirli; Teke, Mustafa; Mercimek, BedrettinThe purpose of the present work is improving stability properties of porcine pancreatic lipase (triacylglycerol lipase, E.C.3.1.1.3) by immobilization on chitosan/TiO2 composite beads. The immobilization parameters were initial enzyme concentration (0.5-2 mg/ml), adsorption time (5-25 min), and glutaraldehyde concentration (1-4 % v/v). The optimum temperature (20-60 A degrees C), optimum pH (3.0-10.0), kinetic parameters, thermal stability (4-70 A degrees C), pH stability (4.0-9.0), and reusability (9 times) were investigated for characterization of immobilized lipase system. The optimum temperatures of free and immobilized lipase were 30 A degrees C. The temperature profile of the immobilized lipase was spread over a large area. The optimum pH values for the free lipase and immobilized lipase were found to be 6.5 and 7.5, respectively. The thermal stability of immobilized lipase was evaluated, and it maintained 45 % activity at 70 A degrees C. But, at this temperature, soluble lipase protected only 15 % activity. Also, the structural characterization of chitosan/TiO2 composite beads was analyzed with scanning electron microscope (SEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and attenuated total reflection Fourier transform infrared spectroscopy analysis (ATR-FTIR). The significance of this study is improving of stability properties of lipase for the industrial usage especially production of biodiesel and dairy products.Öğe The synthesis of a novel DDPHC diazonium salt: Investigation of its usability in the determination of phenol and chlorophenols using CV, SWV and DPV techniques(Elsevier, 2020) Celik, Haci Hasan; Ozcan, Saniye; Mulazimoglu, Aysen Demir; Yilmaz, Ecir; Mercimek, Bedrettin; Cukurovali, Alaaddin; Yilmaz, IbrahimElectrochemical and spectroelectrochemical properties of newly synthesized diazonium salt of 2-(2-(1,3-dioxo- 3,3a-dihydro-1H-isoindol-2(7aH)-yl)-1-(3 methyl-3-phenylcyclobutyl)ethylidene) hydrazinecarboxamide (DDPHC-DAS) were studied using glassy carbon (GC) electrode. In the current study, surface characterization was performed by cyclic voltammetry (CV). Besides electrochemical impedance spectroscopy (EIS) was used for the electrochemical and spectroelectrochemical characterization. Surface images were obtained using scanning electron microscopy (SEM). After completion of modification and characterization process, DDPHC-DAS surface was examined for the usability for the quantitative determination of phenol and chlorophenol derivatives by using CV, square wave voltammetry (SWV) and differential pulse voltammetry (DPV). Phenol and chlorophenol solutions that were prepared in Britton-Robinson (BR) buffer solution (pH 8-12) were employed in this research. The presented study proves that all of compounds can be quantitatively determined not only simultaneously but also independently.
