Browsing by Author "Kivrak, Hilal Demir"

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Electrochemical Production of Graphene Oxide and Its Application as a Novel Hydrogen Peroxide Sensor
(Islamic Azad Univ Tonekabon, 2019) Kivrak, Hilal Demir; Aktas, Nahit; Caglar, Aykut
Herein, graphene oxide is produced by electrochemical oxidation method from graphite rod to examine its hydrogen peroxide sensing ability. The electrochemically produced graphene oxide is characterized by SEM. A few layers of Graphene Oxide (GO) sheets and corrugations in graphene sheets appeared intensely crumpled and folded into a typical wrinkled structure after electrochemical oxidation. Electrochemical measurements are carried out cyclic voltammetry (CV) and chronoamperometry (CA) on graphene oxide and graphite. As a result, graphene oxide exhibits the highest performance toward electrochemical oxidation of H2O2 in 0.1 M phosphate buffered solution (PBS). In addition, CA is employed for the determination of H2O2 at the applied potential of 0.0 V (vs. Ag/AgCl). The electrochemical sensor exhibits fast and selective responses to H2O2 concentration.
Few-Layer Graphene Coated on Indium Tin Oxide Electrodes Prepared by Chemical Vapor Deposition and Their Enhanced Glucose Electrooxidation Activity
(Wiley, 2019) Caglar, Aykut; Ulas, Berdan; Sahin, Ozlem; Kivrak, Hilal Demir
At present, few-layer graphene is deposited on copper (Cu) foil by chemical vapor deposition (CVD) method. Then, the few-layer graphenes produced on the Cu foil are coated onto the indium tin oxide (ITO) electrode to investigate their glucose electrooxidation activities. Hexane and hydrogen flow rate and deposition time parameters with CVD method are examined on different Cu foils. These electrodes are characterized by scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Furthermore, glucose electrooxidation is examined with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. One could note that the graphene network is clearly visible from SEM images. The deconvoluted XPS spectrum indicates that carbon appeared in the form of non-oxygenated ring C atoms for few-layer graphene. The few-layer graphene structure is confirmed by Raman analysis. Few-layer graphene/ITO produced at 5 sccm Hexane and 50 sccm hydrogen flow rate and 20minutes deposition time (G7/ITO) reveals the best electrode activity. The specific activity of G7/ITO electrode is obtained as 6.58mAcm(-2). According to CV, CA, and EIS results, G7/ITO electrode has high electrocatalytic activity, stability, and resistance in comparison with other electrodes.
Investigation of Hydrazine Electrooxidation Performance of Carbon Nanotube Supported Pd Monometallic Direct Hydrazine Fuel Cell Anode Catalysts
(2020) Kivrak, Hilal Demir; Aldemir, Adnan; Cavak, Ali; Er, Ömer Faruk
In this study, carbon nanotube (CNT) supported Pd/CNT catalysts at varying Pd molar ratios (Pd involving among 0.1-20 wt %) are prepared via NaBH4 reduction method. The surface of catalysts prepared for hydrazine electrooxidation are successfully characterized via N2 adsorption-desorption measurements, X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM). Electrochemical measurements are performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. According to the characterization results, for 5% Pd/CNT catalyst, the average particle size and the surface area are determined as 5.17 nm and 773.10 m2 g-1, respectively. Among Pd containing (0.1-20 wt %) CNT supported catalysts, 5%Pd/CNT catalyst exhibits the best current density as 6.81 mA cm-2 (1122.63 mA mg-1 Pd). Furthermore, 5% Pd/CNT catalyst shows the best charge transfer resistance (Rct) compared to Pd/CNT catalysts. Pd/CNT catalysts are promising anode catalysts for direct hydrazine fuel cells.
Novel Ca-125 Antigen Determination in Serum by Electrochemical Methods With Onion Oil-Containing Organo-Hydrogels
(2023) Alpaslan, Duygu; Kivrak, Hilal Demir; Dudu, Tuba Ersen; Er, Ömer Faruk
CA-125 antigen is a glycoprotein that can be found at distinct levels in blood samples according to the phases of ovarian cancer. Herein, we designed novel onion oil-organo-hydrogels (OOHGs) to detect CA-125 antigen at high sensitivity and selectively via electrochemical methods. OOHGs produced are characterized by swelling analysis and Fourier Transform Infrared Spectroscopy (FT-IR). Cyclic voltammetry (CV), Electro impedance spectroscopy (EIS), and Differential pulse voltammetry (DPV) techniques in the potentiostat triple electron system are used for performing the electrochemical measurements. Performances and electron transfer resistances of OOHGs and OOHG+CA-125s are researched via CV and EIS, and the sensitivity properties such as LOD and LOQ of the sensor are determined via DPV. OOHG-2 among OOHGs produced exhibited the highest performance with 0.8151 mA/cm2 (815.1 A/cm2) value at determining CA-125 in serum medium. Moreover, this electrode is found that exhibit a wide linear range like a 1-500 ng/mL concentration range. The limit of quantification (LOQ) and the lowest of detection (LOD) for the OOHG-2 electrode are calculated as 0.531 U/mL and 0.265 U/mL (S/N=3), respectively. Further, the CA-125 antigen of the OOHG-2 electrode in interference results is observed that can be detected with high selectivity. With these results, it can be noted that the OOHG-2 electrode holds great hope for detection ovarian cancer by electrochemical methods.
Ruthenium Modified Defatted Spent Coffee Catalysts for Supercapacitor and Methanolysis Application
(Wiley, 2021) Akdemir, Murat; Hansu, Tulin Avci; Caglar, Aykut; Kaya, Mustafa; Kivrak, Hilal Demir
Currently, a novel green material, defatted spent coffee ground (DSCG), is employed as a support to prepare DSCG supported Ru (DSCG-Ru) material. DSCG and DSCG-Ru materials are characterized by advanced surface analytical techniques such as N-2 adsorption-desorption, X-ray diffraction, X-ray photoelectron spectroscopy, and H-2-temperature-programmed reduction. Characterization results revealed that DSCG-Ru was prepared successfully. First, DSCG-Ru is prepared at varying Ru contents on deoiled coffee waste and hydrogen production experiments are performed by the methanolysis of sodium borohydride on the DSCG-Ru catalysts. It is observed that optimum conditions for the catalyst preparation are examined on the 10% Ru containing DSCG-Ru catalysts and found as 10% Ru, 300 degrees C, and 60 minutes. DSCG catalyst containing 10% Ru completed the methanolysis reaction in 1.5 minutes. Capacitive measurements to investigate the supercapacitor property of DSCG-Ru catalysts prepared at optimum conditions 10% Ru, 300 degrees C, and 60 minutes is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge measurements. Results revealed that gravimetric capacitance of the electrode at a current density is found as of 0.5 A/g and 43 F/g, greater than the literature values. DSCG-Ru, green novel supported Ru catalyst, has a dual promising performance in hydrogen production and supercapacitor measurements.
Synthesis of Pd-ni/C Bimetallic Materials and Their Application in Non-Enzymatic Hydrogen Peroxide Detection
(de Gruyter Open Ltd, 2017) Kazici, Hilal Celik; Salman, Firat; Kivrak, Hilal Demir
In this study, carbon based bimetallic materials (Pd-Ni/C) were synthesized by polyol method in order to increase the hydrogen peroxide reduction catalytic activity of Pd using Ni metal. Hydrogen peroxide reduction and sensing properties of the prepared catalysts were measured by electrochemical methods. As a result, we have established that the addition of Ni at different ratios to Pd has a considerable electrocatalytic effect on H2O2 reduction. This work provides a simple route for preparation of Pd-Ni catalysts to create a very active and sensible electrochemical sensor for H2O2 sensing.