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Öğe A new adsorptive square-wave stripping voltammetric method for the trace analysis of germanium(Hacettepe University, 2008) Gökmeşe, Faruk; Gökmeşe, Ebru; Solak, Ali OsmanThe adsorptive stripping voltammetric determination of trace amounts of germanium(IV) based on the adsorptive accumulation of the germanium(IV)-N-(2-hydroxyphenyl)-3-hydroxysalicylaldimine complex on the hanging mercury drop electrode is reported. The cathodic current of the adsorbed complex was measured by square wave adsorptive stripping voltammetry. The peak potential is at -0.44 V vs. Ag|AgCl|KCl(sat). The effects of various parameters such as ligand and supporting electrolyte (H3PO4) concentrations, accumulation potential and deposition time were investigated. After all optimization processes, the reduction peak was exploited for analytical purposes. The detection limit is 4.7×10-9 M and coefficient of variation is 7.5%. The possible interferences in soil and biological samples by some ions were evaluated in detailÖğe A simple and rapid method for preparing carbon nanopore electrode ensemble by coating a glassy carbon electrode with chromate(Hitit University, 2016) Gökmeşe, Faruk; Gökmeşe, Ebru; Emire, ZuhalA simple preparation method for carbon nanopore electrode ensemble (CNEE) was reported. The CNEE consists of a number of pinholes which remain after coating a carbon surface with chromate. The transformation from transient to steady-state voltammetric behavior of carbon surface was presented. The effect of electrochemical technique to structure of chromate film was investigated. The optimum deposition time and optimum concentration of chromate solution for coating carbon surface substantially were determined for bulk electrolysis (BE) technique. On the other hand for cyclic voltammetry (CV), the effects of scan rate, number of cycle and coating solution concentration on forming uniform partly-insulating layer have been examined. The CNEE prepared by BE technique showed larger hysteresis which means more resistivity than the one prepared by CV. Under the optimum coating conditions the thinner and more useful CNEE with lower resistivity can be prepared by CVÖğe Electrochemical Glucose Detection Using PdAg Nanoparticles Anchored on rGO/MWCNT Nanohybrids(Springer/Plenum Publishers, 2020) Uzunoğlu, Aytekin; Köse, Dursun Ali; Gökmeşe, Ebru; Gökmeşe, FarukThe combination of multi-walled carbon nanotube (MWCNT) and graphene (Gr) to extend their unique physicochemical properties to 3-dimensions (3D) is known to be an effective way to achieve high catalytic properties in electrochemistry. In this context, PdAg metal nanoparticles (MNPs) were anchored on 3-D MWCNT-rGO nanohybrids to construct high-performance enzyme-free electrochemical glucose sensors. The PdAg/MWCNT-rGO nanohybrids were prepared via a one-pot synthesis route and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) methods. The XRD and TEM results confirmed the successful immobilization of PdAg nanoparticles on the support surface and the EDS results revealed a homogeneous MNP distribution. The PdAg content anchored on the hybrids was found to be 39 wt% by TGA analysis, which is compatible with the starting stoichiometric ratio. The constructed sensors showed the sensitivities of 13.16 +/- 0.4 and 5.22 +/- 0.07 mu A mM(-1) cm(-2) in the concentration windows of 0.05 to 4 and 4 to 42 mM, respectively. A wide linear range of 0.05 to 42 mM with a low limit of detection (51 mu M) was obtained from the sensors.Öğe Electrochemical investigation of Zinc(II)-furdap amide complex in DMSO medium(2009) Gökmeşe, Faruk; Gökmeşe, Ebru; Hamurcu, Fatma; Çelikkan, Hüseyin; Aksu, Mehmet LeventThe electrochemical behavior of Zinc(II)-furdap amide complex has been investigated by the use of several electrochemical methods in DMSO on platinum electrode. Both the ligand and the complex gave one electron transfer reduction. Although there was no oxidation peak observed corresponding to the reduction of ligand, there was a corresponding oxidation peak appeared for the complex. The number of electrons transferred was calculated as 1 by the use of bulk electrolysis, rotating disc electrodes employing KouteckTimesNewRomanPSMT.0.5 -Levich equation. The reversibility tests revealed that the reaction followed a quasi reversible mechanism. The mechanism was also confirmed by simulation studies. ks and ? values were found to be 1.0×10-7 cm s-1 and 0.4, respectively. The diffusion coefficient (D) was found as 6.93 ×10-5 cm2 s-1 by the use of Cottrell slope obtained from chronoamperometry experiments and ultra micro disc steady state current (iss). © 2009 Bentham Science Publishers Ltd.Öğe Electrochemical properties of copper complex of Furdap amide in non-aqueous medium(2011) Gökmeşe, EbruThe electrochemical behavior of Cu (II)-Furdap amide complex has been investigated by the use of several electrochemical methods in DMSO on platinum electrode. The number of electrons transferred was calculated by bulk electrolysis and rotating disc electrodes. The reversibility tests were applied to elucidate the reaction mechanism. It was found that the Cu (II)- Furdap complex is reduced with quasi-reversible reaction. The mechanism of the electrode reaction was confirmed by simulation experiments. The standard heterogeneous rate constant (7×10-4 cm s-1), the charge transfer coefficient (0.5), and the diffusion coefficient (1.7×10-6 cm2 s-1) were found by simulation study. © 2011 by ESG.Öğe Fabrication, characterization, and chemical etching of Ag nanoelectrodes(2013) Noel, Jean-Marc; Velmurugan, Jeyavel; Gökmeşe, Ebru; Mirkin, Michael V.The previously developed methodologies for fabricating flat, polished nanoelectrodes were extended to produce silver electrodes with the radii from 50 nm to micrometers. The prepared electrodes were characterized by steady-state voltammetry, scanning electrochemical microscopy (SECM), and atomic force microscopy. The protocol was developed for controlled chemical etching of silver in ammonia solutions to produce recessed nanoelectrodes. Voltammograms and SECM approach curves were obtained to evaluate the recess depth and other geometric parameters of the etched electrodes. © 2012 Springer-Verlag.Öğe Optimization of separation of several sulfonamides in acetonitrile-water binary mixtures by using symmetry shield RP-8 column(Hacettepe University, 2009) Şanlı, Senem; Şanlı, Nurullah; Gökmeşe, Faruk; Gökmeşe, Ebru; Çubuk Demiralay, EbruIn this work, the proportion of organic modifier of the hydro-organic mobile phase was optimized in order to separate twelve compounds namely sulfaguanidine, sulfanilamide, sulfadiazine, sulfathiazole, sulfamethazine, sulfamerazine, sulfamethoxypyridazine, sulfamonomethoxyne, sulfachloropyridazine, sulfadoxine, sulfafurazole and dapson using Symmetry Shield RP-8 Column. Mobile phase was optimized by establishing relationships between retention parameters and Reichardt’s RTN scale of solvent polarity. In addition, selectivity (α) and resolution (RS) values were used in order to establish a general model relating elution behavior of substances with the composition of mobile phase. Logarithm of retention factor corresponding to pure water, log kw, which is the most commonly employed chromatographic hydrophobicity parameter determined by using chromatographic data.Öğe PdAg-decorated three-dimensional reduced graphene oxide-multi-walled carbon nanotube hierarchical nanostructures for high-performance hydrogen peroxide sensing(Cambridge University Press, 2018) Uzunoğlu, Aytekin; Köse, Dursun Ali; Köse, Kazım; Gökmeşe, Ebru; Gökmeşe, FarukHigh-performance electrochemical hydrogen peroxide (H2O2) sensors based on PdAg nanoparticle-decorated reduced graphene oxide (rGO) and multi-walled carbon nanotube (MWCNT) hybrids were developed. The nanostructures were characterized using transmission electron microscopy, scanning electron microscopy, energy-dispersive spectroscopy, thermogravimetric analysis, Fourier transform spectroscopy, and x-ray diffraction techniques. It was found that introduction of MWCNT in the catalyst layer improved the sensitivity and widened the linear range. Sensitivities of 393.2, 437.1, and 576.6 A/mM/cm2 were obtained for PdAg/rGO-MWCNT (2:1), PdAg/rGO-MWCNT (1:1), and PdAg/rGO-MWCNT (1:2), respectively. Furthermore, hierarchical structure of rGO-MWCNT nanohybrids enabled the detection of H2O2 up to 80 mM. Copyright © Materials Research Society 2018.Öğe Platinized carbon nanoelectrodes as potentiometric and amperometric SECM probes(2013) Hu, Keke; Gao, Yang; Wang, Yixian; Yu, Yun; Zhao, Xin; Rotenberg, Susan A.; Gökmeşe, Ebru; Mirkin, Michael V.; Friedman, Gary; Gogotsi, YuryMicrometer-sized platinized carbon electrodes have previously been used for the detection of reactive oxygen and nitrogen species (ROS and RNS) in biological systems. Here, we report the preparation and characterization of quartz-sealed platinized carbon nanoelectrodes. Such electrodes can be employed as tips in the scanning electrochemical microscope (SECM). The prepared electrodes were characterized by steady-state voltammetry, scanning electron microscopy, and SECM. In addition to ROS/RNS detection, the high surface area of a platinized nanoelectrode makes it a useful potentiometric probe. Unlike previously fabricated platinized electrodes, carbon electrodes possess a very thin insulating sheath, which is essential for experiments inside biological cells and high-resolution SECM imaging. © Springer-Verlag Berlin Heidelberg 2013.
