Browsing by Author "Ertaş F.N."
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Item Electrocatalytic oxidation of methanol at Pd and Pt ad-layer modified Au(111) electrodes in alkaline solution(2011) Koçak S.; Dursun Z.; Ertaş F.N.The electrochemical oxidation of methanol was investigated by using various ad-layer modified Au(111) electrodes in alkaline media in comparison to Au(111), polycrystalline Pd, and polycrystalline Pt electrodes. Catalytic activity of gold toward methanol oxidation has tended to increase in more alkaline media, as reflected in the oxidation peak in the concentration range of NaOH (0.1-3.0 M) studied here. The oxidation peak potential of methanol shifted to more negative potentials, indicating a pH-dependent surface reaction. Among the electrodes studied, single-crystal gold electrode surfaces modified with Pd and Pt ad-layers displayed the highest catalytic activity for methanol oxidation. Additional shifts of about 350 mV in the oxidation peak potential of methanol was observed for both ad-layer modified electrodes to more negative potentials compared to that of bare electrodes. The Pd and Pt ad-layer modified Au(111) electrode surfaces did not only supply a superior electrical contact, but also accelerated electron transfer, as shown by the increase in peak current and the positive shift in peak potential. This effect was supported by the doublelayer capacitance measurements of bare Au(111) and Pd ad-layer modified singlecrystal electrodes where the potential of zero charge changed from 15 to 5 mV.Item A spectrophotometric method for determination of molybdenum in water samples by using pyrogallol red and a water soluble ionic liquid(2013) Pelit L.; Koçak S.; Pelit F.O.; Türkmen H.; Ertaş F.N.The present study describes a simple and sensitive spectrophotometric method for the determination of molybdenum in real water samples. The method is based on the hyperchromic and bathochromic effect of an ionic liquid namely, 1-methyl-3-octadecyl-imidazolium bromide (C18mimBr), on molybdenum ion (Mo(vi)) and pyrogallol red (PGR) complex. The ternary complex of Mo-PGR-C18mimBr displays a distinct absorption peak with excellent analytical characteristics and offers the advantages of simplicity for the determination of Mo(vi) ions, without any need for a solvent extraction step. The limit of detection (LOD) and limit of quantification (LOQ) of the method were calculated as 0.74 ng mL-1 and 2.47 ng mL-1 respectively. The method was validated and applied successfully to the determination of Mo(vi) ions in real water samples. The interference of ferric ions was shown to be removed from samples with less ionic content by using an ion exchange resin prior to the analysis, and the performance of the method was compared with that of ICP-MS. © 2013 The Royal Society of Chemistry.Item Electrochemical deposition and behavior of mixed-valent molybdenum oxide film at glassy carbon and ITO electrodes(Elsevier B.V., 2013) Koçak S.; Ertaş F.N.; Dursun Z.The effect of solution composition and the type of the anionic species on the electrochemical formation of mixed-valent molybdenum oxide on a glassy carbon and ITO electrode surfaces was elucidated. Susccessive recording of the voltammograms has shown that anionic species display different stabilizing effect on the reductive formation of hydrogen molybdenum bronzes [MoO 3-x (OH) x ] and chloroacetic acid buffer has given the best results. The deposit was built upon cycling the potential between 0 and -0.9 V (vs. Ag/AgCl) via reduction of Mo(VI) to Mo(V) on the electrode surface in pH 3.0 chloroacetic acid solution. Electrochemical impedance measurements carried out in this medium revealed a shift in potential zero charge values from -0.2 V to -0.55 V after the potential of the GCE had been cycled for 30 min. An establishment of mixed-valent molybdenum oxide deposit by time on the gold electrode surface was proved by quartz crystal microbalance measurements. Atomic force and scanning electron microscopy techniques were made use of so as to characterize the surface structures of the electrodes. X-ray photoelectron spectroscopy studies confirmed that the deposit contains both Mo(V) and Mo(VI). The deposited films exhibited unique catalytic activity towards nitrite oxidation consistent with the change in peak characteristics. © 2012 Elsevier B.V. All rights reserved.Item Molybdenum oxide/platinum modified glassy carbon electrode: A novel electrocatalytic platform for the monitoring of electrochemical reduction of oxygen and its biosensing applications(2013) Çakar I.; Özdokur K.V.; Demir B.; Yavuz E.; Demirkol D.O.; Koçak S.; Timur S.; Ertaş F.N.The reduction of oxygen to water is one of the most important reactions in electrochemistry with regards to the wide range of applications in electrocatalysis, metal corrosion, and fuel cell and mostly in biosensor studies. Present study describes the use of a glassy carbon electrode modified with platinum and molybdenum oxide (Pt-MoOx) in strongly acidic solutions for electrocatalytic reduction of oxygen dissolved in buffer solution for the first time. The dispersion of Pt nanoparticles on MoOx provides larger surface area and better electrocatalytic activity for oxygen reduction and the best response toward dissolved oxygen was obtained with a mole ratio of 1:90 Pt:Mo in deposition solution. The modified surface was then used as a biosensing platform for the monitoring of oxygen consumption due to the bio-catalytic action of glucose oxidase (GOx) as the model enzyme. After optimization of the operational conditions, analytical characterization and application of the glucose oxidase GOx biosensor to flow injection analysis mode have been successfully performed. © 2013 Published by Elsevier B.V. All rights reserved.Item Centri-voltammetric determination of molybdenum(Royal Society of Chemistry, 2013) Koçak S.; Ertaş F.N.Centri-voltammetry is a method developed in the last decade which combines the advantages of centrifugation and voltammetry and hence provides a practical way for application of co-precipitation in trace analysis allowing direct voltammetric scan. The present study describes another application of the centri-voltammetric method for the determination of biologically essential trace elements, in particular, molybdenum ion. For this purpose, a dual-functional voltammetric cell adjustable to the centrifuge was designed and utilized in the determination of molybdenum ions with various carrier reagents, i.e. oxine, pyrogallol red, and cupferron. Optimization studies include solution properties as well as voltammetric measurement and centrifugal parameters. Among the reagents studied, the best results were obtained with pyrogallol red and the reduction peak current of the complex was utilized for analytical purposes. The limit of detection from calibration curves was calculated to be 9.4 × 10-9 M and a better sensitivity was obtained in the presence of chlorate ions that are known to have a catalytic effect on the reaction. The method was employed in the determination of molybdenum in milk samples and the results were compared with those obtained by the ICP-MS method. © The Royal Society of Chemistry 2013.Item Electrochemical preparation, characterization of molybdenum-oxide/platinum binary catalysts and its application to oxygen reduction reaction in weakly acidic medium(Elsevier Ltd, 2015) Yavuz E.; Özdokur K.V.; Çakar I.; Koҫak S.; Ertaş F.N.This study reports a detailed analysis of an electrode material containing molybdenum oxide and platinum nanoparticles which shows superior catalytic effect towards to oxygen reduction in weakly acid medium. The material is sequentially electrodeposited on a glassy carbon electrode from aqueous solutions of MoO 4 2- and PtCl 4 2- either by cycling the potential or by applying pulsed potential technique. Chemical and morphological characterization of the electrode surface was made by X-ray photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The electrode performance towards oxygen reduction reaction was investigated in pH 5.0 acetate buffer solution saturated with oxygen and parameters such as the cell content and electrodeposition conditions were optimized. The performance of the electrode was compared with Pt disk, bare glassy carbon, platinum modified glassy carbon electrodes along with the electrode modified in a single step and named as Pt-MoO x /GCE. Overall results indicated that sequentially deposited molybdenum oxide and platinum modified glassy carbon electrode designated as Pt/MoO x /GCE has shown higher catalytic activity considering the peak location and current intensities. This was consisted with the pulsed electrodeposition process and even higher catalytic activity was obtained than the electrode modified by cycling voltammetry. © 2014 Elsevier Ltd. All rights reserved.Item Development of pulsed deposited manganese and molybdenum oxide surfaces decorated with platinum nanoparticles and their catalytic application for formaldehyde oxidation(Elsevier Ltd, 2016) Özdokur K.V.; Tatli A.Y.; Yilmaz B.; Koçak S.; Ertaş F.N.Manganese and molybdenum mixed oxides were co-deposited in a thin film form by pulsed deposition technique on a glassy carbon substrate, and this mixed oxide film was further decorated with platinum nanoparticles. Formaldehyde, being a candidate for proton exchange membrane fuel cell applications, was chosen as the test material for the catalytic activities of the developed surface in alkaline media. The synergetic effect of the mixed metal oxide deposit incorporating Pt nanoparticles was verified by using different mol ratios of the corresponding metal ions and applying pulsed deposition conditions and under optimized conditions and, resultant oxidation peak has shown a significant increase in the peak current accompanied by the small shift in the peak potential. The modified composite electrodes were characterized by SEM, EDX, XPS and EIS. © 2016 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Item Nanostructured Metal–Metal Oxides and Their Electrocatalytic Applications(wiley, 2018) Özdokur K.V.; Koçak S.; Ertaş F.N.Electrochemical nanotechnologies have witnessed great fundamental advances in the last two decades. The strong interaction between the nanoscience and electrochemistry has led intensified studies on nanostructured materials for electronic, electrochromic, catalytic, and analytical applications. Many researchers have focused on metallic and carbon-based nanomaterials for electrocatalysis, energy conversion systems, and sensor development. The requirement of improvement of the performance of conventional Pt-based catalysts along with the search for low cost alternatives has led to the development of multicomponent catalysis systems. Due to their abundant sources and low cost, transition metal oxides offer a wide range of applications in various fields. However, their performance was found to be dependent on the synthesis procedure. Electrochemical deposition is usually the method of choice not only because this technique is a more practical and economical way for readily producing large uniform oxide thin films but also because the technique provides the controlling of the nature of the deposit by changing the deposition parameters. By this means, a mixed-valent metal oxide (MeOx) film can be produced on a carbon or other substrates, which is believed to be responsible for their catalytic activities. Further improvement in the catalytic performance can be maintained by the combination of hyper-d electronic noble metals, platinum in particular, with hypo-d electronic transition metal oxides. This chapter also covers the recently developed deposition techiques such as electrochemical pulsed deposition (PD). This technique favors the formation of nucleation sites and hence contributes to a high dispersion of the deposits compared to other methods. The performance of the electrode on both anodic and cathodic directions can be further enhanced by decorating with metallic nanoparticles and carbon nanotubes. © 2019 Scrivener Publishing LLC.Item Pulsed Deposited Manganese and Vanadium Oxide Film Modified with Carbon Nanotube and Gold Nanoparticle: Chitosan and Ionic Liquid-based Biosensor(Wiley-VCH Verlag, 2020) Akoğulları S.; Çιnar S.; Özdokur K.V.; Aydemir T.; Ertaş F.N.; Koçak S.Present study describes the synthesis of mixed oxide films of manganese and vanadium by electrochemical pulsed deposition technique on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNT). The film was further decorated with gold nanoparticles to enhance the reduction signal of dissolved oxygen in pH 5.17 acetate buffer solution. All of the electrochemical synthesized modified electrodes have been characterized with Scanning electron microscopy(SEM), High-resolution transmission electron microscopy (HRTEM), X-Ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD) techniques. The electrode obtained (AuNPs/MnOx−VOx/CNT/GCE) was utilized as a platform for glucose biosensor where the glucose oxidase enzyme was immobilized on the composite film with the aid of chitosan and an ionic liquid. The electrochemical performance of the biosensor was investigated by cyclic voltammetry and the relative parameters have been optimized by amperometric measurements in pH 5.17 acetate buffer solution. The developed biosensor exhibited a linear range for glucose between 0.1–1.0 mM and the limit of detection was calculated as 0.02 mM. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, WeinheimItem Development of cobalt oxide film modified electrode decorated with platinum nanoparticles as a biosensing platform for phenol(Taylor and Francis Ltd., 2020) Kuşcu C.; Özdokur K.V.; Koçak S.; Ertaş F.N.Recently, cobalt oxides attract a special attention mainly due to their excellent electrocatalytic activity towards various compounds. This study concerns with electrochemical preparation of cobalt oxide modified glassy carbon electrodes decorated with platinum nanoparticle in the pursuit of its catalytic applications. The parameters affecting the deposition conditions have been evaluated by monitoring oxygen reduction reaction (ORR) in pH 5.0 acetate buffer. Under optimal conditions, the composite film electrode surface was utilised as a platform forbiosensor development. Polyphenol oxidase enzyme was immobilised onto the electrode surface for phenol detection, and the influence of solution and operational parameters have been investigated. The medium pH and the enzyme amount have been optimised as pH 7.0 and 0.3 mg, respectively. Chronoamperograms were recorded for phenol detection in micromolar levels. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.