Browsing by Author "Koçak, S"

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    Simultaneous electrochemical determination of hydrazine and nitrite based on Au nanoparticles decorated on the poly(Nile Blue) modified carbon nanotube
    Hatip, M; Koçak, S; Dursun, Z
    In this study, simultaneous determination of toxic hydrazine and nitrite was performed on composite electrodes of poly(Nile blue)(NB), carbon nanotube(CNT) and gold nanoparticles(AuNPs). The prepared AuNPs/CNT/poly(NB)/GCE was used for as a sensor platform for individual and simultaneous determination of hydrazine and nitrite. Electrodes were characterized by HRTEM, SEM, XPS, EIS. The LOD for nitrite and hydrazine was 5.0 mu M and 3.1 mu M at AuNP/CNT/poly(NB)/GCE, respectively. Also, sensitive amperometric determinations of hydrazine and nitrite were performed and LOD were calculated as 0.33 mu M and 0.68 mu M, respectively. The method was applied to sausage and river water samples and recovery results were obtained in the range 85-115 %.
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    Electrocatalytic oxidation of methanol at Pd and Pt ad-layer modified Au(111) electrodes in alkaline solution
    Koçak, S; Dursun, Z; Ertas, FN
    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.
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    Electrochemical Determination of Hydrazine at Gold and Platinum Nanoparticles Modified Poly(L-Serine) Glassy Carbon Electrodes
    Koçak, S; Altin, A; Koçak, ÇC
    L-serine monomer was polymerized electrochemically on a glassy carbon electrode by cyclic voltammetry. After L-serine polymerization, gold and platinum metal nanoparticles were doped by electrochemical reduction on the surface. The modified electrodes were characterized by using scanning electron microscopy and electrochemical impedance spectroscopy. The electrochemical behavior of hydrazine oxidation at the electrodes was investigated in 0.1M pH 7.0 phosphate buffer. Hydrazine oxidation peaks were observed at 650, 399, 280, and -395mV at the bare glassy carbon, poly(L-serine) modified glassy carbon, gold nanoparticle modified poly(L-serine) film glassy carbon electrode, and platinum nanoparticles modified poly(L-serine) film glassy carbon electrode, respectively. The most active surface towards hydrazine oxidation was the platinum nanoparticle modified poly(L-serine) film glassy carbon electrode with a 1045mV negative potential shift and approximately three-fold higher peak current. The hydrazine oxidation peak was shifted to a 370mV negative potential with a 2.5 times higher current at the gold nanoparticle modified poly(L-serine) film glassy carbon electrode compared to the bare electrode. The linear concentration ranges were from 1.0 to 1000 mu M and 0.5 to 1000 mu M for the gold nanoparticle modified poly(L-serine) film glassy carbon and the platinum nanoparticles modified poly(L-serine) film glassy carbon electrodes with limits of detections of 0.5 and 0.2 mu M, respectively.
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    Electrochemical Determination of Sesamol in Foods by Square Wave Voltammetry at a Boron-Doped Diamond Electrode
    Aslisen, B; Koçak, ÇC; Koçak, S
    Sesamol is a phenolic compound naturally found in sesame seeds. It has beneficial health effects in humans, as it features significant antioxidant activity and has anticancer and anti-aging properties. Therefore, finding a suitable electrode surface for sesamol determination is important. The prominent advantage of boron-doped diamond electrodes is their use in many sensing platforms without the need for the surface modification. This study represents the first time that sesamol has been determined using boron-doped diamond electrodes in acidic media by square wave voltammetry. Linear responses of sesamol were obtained in the concentration range from 0.2 mu M to 1000 mu M, and the detection limit was determined to be 85 nM based on a signal-to-noise ratio of 3. The relative standard deviations were 2.1% for a 1 mu M standard with three measurements.
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    Electrochemical Preparation and Characterization of Gold and Platinum Nanoparticles Modified Poly(taurine) Film Electrode and Its Application to Hydrazine Determination
    Koçak, ÇC; Altin, A; Aslisen, B; Koçak, S
    A highly sensitive hydrazine sensor has been developed by using gold and platinum nanoparticles (NPs) decorated poly(taurine) on modified glassy carbon electrode (GCE). First, poly(taurine) modified glassy carbon electrode was prepared by electropolymerization method using cyclic voltammetry. Then, a thin layer of poly(taurine) is coated electrochemically on a GCE and the effective parameters have been optimized. After taurine polymerization, metal nanoparticles (Au and Pt) were doped by electrochemical reduction from metal ions solution on poly(taurine)/GCE surface. Modified electrodes were characterized by using different surface techniques. The obtaining results were compared with bare GCE, poly(taurine) modified glassy carbon electrode, AuNPs/poly(taurine)/GCE, and PtNPs/poly(taurine)/GCE. The peak potential of hydrazine oxidation on bare GCE, poly(taurine)/GCE, AuNPs/poly(taurine)/GCE, and PtNPs/poly(taurine)/GCE were observed at 690 mV, 401 mV, 341 mV, and -370 mV, respectively. Finally, these modified electrodes were successfully used for the oxidation of hydrazine and exhibited excellent electrocatalytic activity with respect to hydrazine oxidation. The better sensitivity and selectivity exhibited the amperometric techniques to compare other techniques. The linear concentration ranges were found between 0.1 to 1000 mu M (R-2 = 0.9981) for AuNPs/poly(taurine)/GCE. The limit of detection (LOD) and limit of quantitation (LOQ) values were calculated to be 0.05 mu M and 0.15 mu M, respectively. The practical application of the sensor was evaluated in river water samples with good recoveries.
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    Lead and copper removal using Kula volcanics from environmental waters
    Yayayürük, O; Yayayürük, AE; Koçak, Ç; Koçak, S
    The ability of Kula volcanics (the youngest volcanic rocks of western Anatolia) to remove Pb(II) and Cu(II) from aqueous solutions has been demonstrated, for the first time, in this study. The optimum parameters viz., pH, contact time and sorbent amount/solution volume ratio were evaluated using batch experiments. Langmuir isotherm model excellently described the sorption process and both of the ions followed pseudo-second-order kinetics. The method was applied to the natural river water samples and it was observed that the sorbent can successfully be used for the removal Pb(II) and Cu(II) ions with acceptable accuracy and precision.
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    Highly improved electrocatalytic oxidation of dimethylamine borane on silver nanoparticles modified polymer composite electrode
    Koçak, CC; Koçak, S; Karabiberoglu, S; Dursun, Z
    Dimethylamine borane (DMAB) is a promising fuel alternative for fuel cell applications. In this work cyclic voltammetric behavior of DMAB was investigated on the polymerized aminophenol film decorated with Ag nanoparticles in alkaline media. The polymer film was formed on the glassy carbon electrode by electrochemical technique and then, the surface was modified with Ag nanoparticles. The surface of the modified electrode was identified by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy techniques. The developed electrode has displayed high electrocatalytic activity for DMAB oxidation in alkaline media depending on the supporting electrolyte concentration. Experimental parameters such as cycle number used in electropolymerization of p-aminophenol, deposition of Ag nanoparticles and supporting electrolyte were optimized.
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    Pulsed Deposited Manganese and Vanadium Oxide Film Modified with Carbon Nanotube and Gold Nanoparticle: Chitosan and Ionic Liquid-based Biosensor
    Akogullari, S; Çinar, S; Özdokur, KV; Aydemir, T; Ertas, FN; 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.
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    Polymer Film Supported Bimetallic Au-Ag Catalysts for Electrocatalytic Oxidation of Ammonia Borane in Alkaline Media
    Karabiberoglu, SU; Koçak, CC; Koçak, S; Dursun, Z
    Ammonia borane is widely used in most areas including fuel cell applications. The present paper describes electrochemical behavior of ammonia borane in alkaline media on the poly(p-aminophenol) film modified with Au and Ag bimetallic nanoparticles. The glassy carbon electrode was firstly covered with polymeric film electrochemically and then, Au, Ag, and Au-Ag nanoparticles were deposited on the polymeric film, respectively. The surface morphology and chemical composition of these electrodes were examined by scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that alloyed Au-Ag bimetallic nanoparticles are formed. Electrochemical measurements indicate that the developed electrode modified by Au-Ag bimetallic nanoparticles exhibit the highest electrocatalytic activity for ammonia borane oxidation in alkaline media. The rotating disk electrode voltammetry demonstrates that the developed electrode can catalyze almost six-electron oxidation pathway of ammonia borane. Our results may be attractive for anode materials of ammonia borane fuel cells under alkaline conditions.
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    Development of a novel hydrothermal process for surface modification of galvanized steel, characterization, and photocatalytic application
    Zorlu, R; Ozdokur, KV; Acimert, ÖB; Demir, Z; Çaglar, B; Çirak,Ç; Koçak, S
    In this study, the hydrothermal surface modification of galvanized steel was performed on the substrate without any precursor ion for the first time to achieve a photocatalytic activity under UV light irradiation. The structural, morphological and optical properties of the modified and bare samples were examined by XRD, SEM-EDX, XPS, FTIR, UV-DRS and PL analyses. Electrochemical and wettability properties were determined with potentiostat and contact angle goniometry, respectively. The photocatalytic performances of surface modified galvanized steel samples were also investigated and comparatively evaluated by photo-degradation of quinoline yellow dye under UV light irradiation. Upon the doping silver ions into the structure, the photocatalytic degradation efficiency of fabricated composite material was determined as 100 % after the periods of 65 min. To the best of our knowledge this study is the first study dealing with photodegradation of quinolone yellow by using modified galvanized samples. The modified galvanized steel samples exhibited 96.1 % of its initial activity after 5 cycles. The surface modification by hydrothermal treatment improved the electrochemical properties of galvanized steel.
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    Molybdenum oxide/platinum modified glassy carbon electrode: A novel electrocatalytic platform for the monitoring of electrochemical reduction of oxygen and its biosensing applications
    Çakar, I; Özdokur, KV; Demir, B; Yavuz, E; Demirkol, DO; Koçak, S; Timur, S; Ertas, FN
    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 (GO(x)) as the model enzyme. After optimization of the operational conditions, analytical characterization and application of the glucose oxidase GO(x) biosensor to flow injection analysis mode have been successfully performed. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.
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    Simultaneous differential pulse polarographic determination of cadmium, lead, and copper in milk and dairy products
    Tokusoglu, Ö; Aycan, S; Akalin, S; Koçak, S; Ersoy, N
    The contents of potentially toxic elements lead and cadmium and the essential element copper in various milk and dairy products consumed in Turkey were determined by differential pulse polarography (DPP), primarily to assess whether the intakes comply with recommended desired concentrations for essential and permissible levels for toxic elements. A simple and rapid DPP method has been developed for the simultaneous determination of cadmium, lead, and copper in samples. Using the differential pulse mode, half-wave peak potentials as E-1/2 were -0.58, -0.40, and -0.07 V for cadmium (Cd), lead (Pb), and copper (Cu), respectively. Marketed formulations of dairy products have been analyzed by calibration and standard addition methods. Recovery experiments were found to be quantitative. The linear domain ranges were 0.00-674.28 mug/L for Cd (R-2 = 0.9999), 0.19-2.94 mg/L (p < 0.01) for Pb (R-2 = 0.9997), and 0.41 -133.46 mug/L for Cu (p < 0.01) (R-2 = 0.9999). The studies have shown that the method is a rapid, reproducible, and accurate determination of these elements in milk and dairy products and can be used in the analysis of marketed formulations in the milk and dairy industry.
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    Electrochemical Preparation, Characterization of Molybdenum-Oxide/Platinum Binary Catalysts and Its Application to Oxygen Reduction Reaction in Weakly Acidic Medium
    Yavuz, E; Özdokur, KV; Çakar, I; Koçak, S; Ertas, FN
    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 MoO42 and PtCl42 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-MoOx/GCE. Overall results indicated that sequentially deposited molybdenum oxide and platinum modified glassy carbon electrode designated as Pt/MoOx/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. (C) 2014 Elsevier Ltd. All rights reserved.
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    Development of pulsed deposited manganese and molybdenum oxide surfaces decorated with platinum nanoparticles and their catalytic application for formaldehyde oxidation
    Özdokur, KV; Tatli, AY; Yilmaz, B; Koçak, S; Ertas, FN
    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. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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    Sensitive determination of hydrazine using poly(phenolphthalein), Au nanoparticles and multiwalled carbon nanotubes modified glassy carbon electrode
    Hatip, M; Koçak, S; Dursun, Z
    This study reports a detailed analysis of an electrode material containing poly(phenolphthalein), carbon nanotubes and gold nanoparticles which shows superior catalytic effect towards to hydrazine oxidation in Britton-Robinson buffer (pH 10.0). Glassy carbon electrode was modified by electropolymerization of phenolphthalein (PP) monomer (poly(PP)/GCE) and the multiwalled carbon nanotubes (MWCNTs) was dropped on the surface. This modified surface was electrodeposited with gold nanoparticles (AuNPs/CNT/poly(PP)/GCE). The fabricated electrode was analysed the determination of hydrazine using cyclic voltammetry, linear sweep voltammetry and amperometry. The peak potential of hydrazine oxidation on bare GCE, poly(PP)/GCE, CNT/GCE, CNT/poly(PP)/GCE, and AuNPs/CNT/poly(PP)/GCE were observed at 596 mV, 342 mV, 320 mV, 313 mV, and 27 mV, respectively. A shift in the overpotential to more negative direction and an enhancement in the peak current indicated that the AuNPs/CNT/poly(PP)/GC electrode presented an efficient electrocatalytic activity toward oxidation of hydrazine. Modified electrodes were characterized with High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Amperometric current responses in the low hydrazine concentration range of 0.25-13 mu M at the AuNPs/CNT/poly(PP)/GCE. The limit of detection (LOD) value was obtained to be 0.083 mu M. A modified electrode was applied to naturel samples for hydrazine determination.
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    Development of cobalt oxide film modified electrode decorated with platinum nanoparticles as a biosensing platform for phenol
    Kuscu, C; Özdokur, KV; Koçak, S; Ertas, FN
    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.
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    A spectrophotometric method for determination of molybdenum in water samples by using pyrogallol red and a water soluble ionic liquid
    Pelit, L; Koçak, S; Pelit, FO; Türkmen, H; Ertas, FN
    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 (C(18)mimBr), on molybdenum ion (Mo(VI)) and pyrogallol red (PGR) complex. The ternary complex of Mo-PGR-C(18)mimBr 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.
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    Enhanced Electrochemical Determination of Catechol and Hydroquinone Based on Pd Nanoparticles/Poly(Taurine) Modified Glassy Carbon Electrode
    Koçak, ÇC; Koçak, S
    Here, Pd nanoparticles and poly(taurine) film was prepared on the glassy carbon electrode surface (Pd/Poly(TAU)/GCE) by the rapid electrochemical technique. The proposed composite surface was characterized by scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS) and electrochemical impedance spectroscopy(EIS). Enhanced electron transfer ability and higher electroactive surface area were achieved at Pd/Poly (TAU)/GCE as compared to the bare GCE and polymer film electrode. The new and highly stable Pd/Poly(TAU)/GCE was employed for the individual and simultaneous determination of hydroquinone and catechol which were environmentally toxic. Under the optimized conditions, HQ and CC were individually determined by using the differantial pulse voltammetry in the linear ranges of 0.008-100 mu M and 0.001-100 mu M with the detection limits of (LOD) 2.1 nM and 0.68 nM, respectively. In case of simultaneous determination, LODs were found as 10 nM and 0.88 nM for HQ and CC, respectively. The content of both analytes in the real sample analysis was evaluated in the river water and tap water successfully.
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    Determination of Hydrazine at a Platinum Nanoparticle and Poly(Bromocresol Purple) Modified Carbon Nanotube Electrode
    Koçak, S; Aslisen, B; Koçak, ÇC
    Bromocresol purple was polymerized electrochemically at a carbon nanotube modified glassy carbon electrode and platinum nanoparticles were doped on the polymer film by electrochemical reduction. The modified electrodes were characterized by electrochemical impedance spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The oxidation of hydrazine was investigated at the platinum nanoparticle modified electrode in phosphate buffer. The results were compared with those obtained using other modified and bare electrodes. The best catalytic activity was obtained at the platinum nanoparticle modified electrode due to shift of the oxidation peak to more negative values and highest current. The peak potential and current for hydrazine were -445mV and 175.5 mu A, respectively. Linear calibration curves for hydrazine were obtained from 10 to 1000mM. The limits of detection and quantitation for hydrazine were 1.0 and 3.0mM, respectively.
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    Hydrazine oxidation at gold nanoparticles and poly(bromocresol purple) carbon nanotube modified glassy carbon electrode
    Koçak, S; Aslisen, B
    Bromocresol purple monomers were polymerized electrochemically at carbon nanotube modified glassy carbon electrode surface and obtained electrodes were donated as poly(BCP)/CNT/GCE. After electrochemical polymerization, Au nanoparticles were doped on the polymer film carbon nanotube modified glassy carbon electrode surface by electrochemical reduction from their acidic solutions. Modified electrodes are characterized with electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) techniques. The electrochemical behavior of hydrazine oxidation was investigated at gold nanoparticles modified poly(BCP)/CNT electrodes in pH 10.0 phosphate buffer solution. The obtained results were compared with other modified electrodes. The best catalytic activity was obtained at AuNPs/poly(BCP)/CNT/GCE due to the shift of oxidation peak to more negative values than other electrodes with a higher current value. The peak potential and current oxidation of hydrazine were obtained at AuNPs/poly(BCP)/CNT/GCE (-28 mV, 205 mu A) and poly(BCP)/CNT/GCE (427 mV, 80 mu A). Under optimal conditions, the calibration curves for hydrazine were obtained over the range of 5.0 x 10(-7)-1.0 x 10(-3) M. The limit of detection for hydrazine was calculated as 1.0 x 10(-7) M for AuNPs/poly(BCP)/CNT/GCE. (C) 2014 Elsevier B.V. All rights reserved.