K. Özdokur | Ege University (original) (raw)

Papers by K. Özdokur

Sensors and Actuators B: Chemical, 2014

Present study reports the use of a glassy carbon electrode modified with manganese oxide decorate... more Present study reports the use of a glassy carbon electrode modified with manganese oxide decorated with platinum nanoparticles (Pt-MnO x /GCE) for electrocatalytic reduction of oxygen dissolved in buffer solution. The electrode exhibits better electrocatalytic activity toward oxygen reduction than bulk platinum due to larger surface area of manganese oxide which also prevents agglomeration of platinum nanoparticles. Best results were obtained with the electrode modified by cycling the potential in a range of −0.25-1.05 V for five times in a cell containing 1.0 mM K 2 PtCl 6 and 0.1 M MnSO 4 in 0.01 M H 2 SO 4 solution. Then, the electrode developed was utilized as a biosensing platform for the monitoring of oxygen consumption due to the bio-catalytic activity of pyranose oxidase. In the pursuit of a stable and rapid response the biocomponent was bridged with an ionic liquid namely 1-butyl-3-methyl imidazolium hexaflourophosphate. Chronoamperometric measurement of oxygen at 0.2 V gave 0.010-0.100 mM linear range with a detection limit of 2.0 M and sensitivity of 6.1 nA M −1 under optimized conditions. In addition, ionic liquid provides a conductive environment which shortens the response time to 3 s for low concentrations. Overall results indicated that fabricated biosensor is a good candidate for automated systems.

Analytical Letters, 2015

ABSTRACT A novel polymer-clay composite solid phase microextraction fiber is reported for the ads... more ABSTRACT A novel polymer-clay composite solid phase microextraction fiber is reported for the adsorption of methanol in biodiesel with subsequent determination by gas chromatography coupled with a flame ionization detector. The fiber was fabricated using a stainless steel wire that was subjected to electropolymerization in 0.1 molar NaClO4 containing thiophene and montmorillonite clay dispersed in acetonitrile. Electrochemical deposition was maintained by cycling the potential from −0.2 to + 2.2 volts at a scan rate of 50 millivolts per second. Examination of the surface by scanning electron microscopy revealed that the fiber had a porous surface suitable for the adsorption of volatile analytes. The properties of the fiber were investigated by thermogravimetric analysis and infrared spectroscopy that showed that the clay was inserted in the structure. The fiber was exposed to methanol in biodiesel. The adsorption time, adsorption temperature, and desorption temperature were optimized. Under the optimized conditions, the linear dynamic range for methanol extended from 0.029 to 0.24 percent (m/m) with a limit of detection of 0.009 percent (m/m). The method was employed for the analysis of biodiesel and the results were validated with a standard EN 14110 method.

Sensors and Actuators B: Chemical, 2013

Talanta, 2012

Present paper describes the results of a novel method which combines the Head space (HS) preconce... more Present paper describes the results of a novel method which combines the Head space (HS) preconcentration of the analyte on the electrode prior to the voltammetric analysis. Thereafter, the method was called HS-Voltammetry. The performance of the method was tested upon using an electroactive and volatile molecule, phenol molecule, which gives an oxidation peak at conventional electrodes. In this study, a glassy carbon electrode was modified with polypyrrole by electropolymerization and then, the electrode was placed over the solution in a sealed vial heated gently on a hotplate with a stirrer for phenol determination. By controlling the thickness of the polymeric coating and optimizing preconcentration parameters such as vial pH and temperature, stirring rate and exposure time, a very consistent (5.2% at 5.0 Â 10 À 7 M) fraction of the analyte can be extracted during a predetermined time. The oxidation peak current at 0.8 V depended linearly on the phenol concentration over a wide range (3 orders of magnitude). The detection limit was estimated as 7.0 Â 10 À 8 M at 60 1C (S/N¼ 3) which is well below the limit set by the European Community for phenols in wastewaters (ca. 5 Â 10 À 6 M). The effect of other phenolic compounds was also examined and it was shown that head space preconcentration eliminated the interference of non-volatile phenolic acids studied. For volatile phenolic compounds, the selectivity can be maintained in cases when isolated peaks are obtained for each component. The proposed method has been applied successfully for the determination of phenol in artificial wastewater and recovery percentage was calculated as 93%.

Journal of Chromatography B, 2013

Keywords: Polypyrrole fiber Head space solid phase micro extraction Endocrine disruptor pesticide... more Keywords: Polypyrrole fiber Head space solid phase micro extraction Endocrine disruptor pesticide Gas chromatography Red wine a b s t r a c t A robust in house solid-phase micro extraction (SPME) surface has been developed for the headspace (HS)-SPME determination of endocrine disruptor pesticides, namely, Chlorpyrifos, Penconazole, Procymidone, Bromopropylate and Lambda-Cyhalothrin in wine sample by using sodium dodecylsulfate doped polypyrrole SPME fiber. Pyrrole monomer was electrochemically polymerized on a stainless steel wire in laboratory conditions in virtue of diminishing the cost and enhancing the analyte retention on its surface to exert better selectivity and hence the developed polymerized surface could offer to analyst to exploit it as a fiber in headspace SPME analysis. The parameters, mainly, adsorption temperature and time, desorption temperature, stirring rate and salt amount were optimized to be as 70 • C and 45 min, 200 • C, 600 rpm and 10 g L −1 , respectively. Limit of detection was estimated in the range of 0.073-1.659 ng mL −1 for the pesticides studied. The developed method was applied in to red wine sample with acceptable recovery values (92-107%) which were obtained for these selected pesticides.

Electrochimica Acta, 2015

Highlights  The electrode is deposited cycling the potential or pulsed potential technique  PtN... more Highlights  The electrode is deposited cycling the potential or pulsed potential technique  PtNPs/MoOx/GCE shows superior catalytic effect towards to ORR  The surface is characterized with XPS, SEM, EIS and cyclic voltammetry.  The higher catalytic activity was obtained in the pulsed electrodeposition process Abstract 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 2and PtCl 4 2either 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 A C C E P T E D M A N U S C R I P T 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

Sensors and Actuators B: Chemical, 2014

Present study reports the use of a glassy carbon electrode modified with manganese oxide decorate... more Present study reports the use of a glassy carbon electrode modified with manganese oxide decorated with platinum nanoparticles (Pt-MnO x /GCE) for electrocatalytic reduction of oxygen dissolved in buffer solution. The electrode exhibits better electrocatalytic activity toward oxygen reduction than bulk platinum due to larger surface area of manganese oxide which also prevents agglomeration of platinum nanoparticles. Best results were obtained with the electrode modified by cycling the potential in a range of −0.25-1.05 V for five times in a cell containing 1.0 mM K 2 PtCl 6 and 0.1 M MnSO 4 in 0.01 M H 2 SO 4 solution. Then, the electrode developed was utilized as a biosensing platform for the monitoring of oxygen consumption due to the bio-catalytic activity of pyranose oxidase. In the pursuit of a stable and rapid response the biocomponent was bridged with an ionic liquid namely 1-butyl-3-methyl imidazolium hexaflourophosphate. Chronoamperometric measurement of oxygen at 0.2 V gave 0.010-0.100 mM linear range with a detection limit of 2.0 M and sensitivity of 6.1 nA M −1 under optimized conditions. In addition, ionic liquid provides a conductive environment which shortens the response time to 3 s for low concentrations. Overall results indicated that fabricated biosensor is a good candidate for automated systems.

Analytical Letters, 2015

ABSTRACT A novel polymer-clay composite solid phase microextraction fiber is reported for the ads... more ABSTRACT A novel polymer-clay composite solid phase microextraction fiber is reported for the adsorption of methanol in biodiesel with subsequent determination by gas chromatography coupled with a flame ionization detector. The fiber was fabricated using a stainless steel wire that was subjected to electropolymerization in 0.1 molar NaClO4 containing thiophene and montmorillonite clay dispersed in acetonitrile. Electrochemical deposition was maintained by cycling the potential from −0.2 to + 2.2 volts at a scan rate of 50 millivolts per second. Examination of the surface by scanning electron microscopy revealed that the fiber had a porous surface suitable for the adsorption of volatile analytes. The properties of the fiber were investigated by thermogravimetric analysis and infrared spectroscopy that showed that the clay was inserted in the structure. The fiber was exposed to methanol in biodiesel. The adsorption time, adsorption temperature, and desorption temperature were optimized. Under the optimized conditions, the linear dynamic range for methanol extended from 0.029 to 0.24 percent (m/m) with a limit of detection of 0.009 percent (m/m). The method was employed for the analysis of biodiesel and the results were validated with a standard EN 14110 method.

Sensors and Actuators B: Chemical, 2013

Talanta, 2012

Present paper describes the results of a novel method which combines the Head space (HS) preconce... more Present paper describes the results of a novel method which combines the Head space (HS) preconcentration of the analyte on the electrode prior to the voltammetric analysis. Thereafter, the method was called HS-Voltammetry. The performance of the method was tested upon using an electroactive and volatile molecule, phenol molecule, which gives an oxidation peak at conventional electrodes. In this study, a glassy carbon electrode was modified with polypyrrole by electropolymerization and then, the electrode was placed over the solution in a sealed vial heated gently on a hotplate with a stirrer for phenol determination. By controlling the thickness of the polymeric coating and optimizing preconcentration parameters such as vial pH and temperature, stirring rate and exposure time, a very consistent (5.2% at 5.0 Â 10 À 7 M) fraction of the analyte can be extracted during a predetermined time. The oxidation peak current at 0.8 V depended linearly on the phenol concentration over a wide range (3 orders of magnitude). The detection limit was estimated as 7.0 Â 10 À 8 M at 60 1C (S/N¼ 3) which is well below the limit set by the European Community for phenols in wastewaters (ca. 5 Â 10 À 6 M). The effect of other phenolic compounds was also examined and it was shown that head space preconcentration eliminated the interference of non-volatile phenolic acids studied. For volatile phenolic compounds, the selectivity can be maintained in cases when isolated peaks are obtained for each component. The proposed method has been applied successfully for the determination of phenol in artificial wastewater and recovery percentage was calculated as 93%.

Journal of Chromatography B, 2013

Keywords: Polypyrrole fiber Head space solid phase micro extraction Endocrine disruptor pesticide... more Keywords: Polypyrrole fiber Head space solid phase micro extraction Endocrine disruptor pesticide Gas chromatography Red wine a b s t r a c t A robust in house solid-phase micro extraction (SPME) surface has been developed for the headspace (HS)-SPME determination of endocrine disruptor pesticides, namely, Chlorpyrifos, Penconazole, Procymidone, Bromopropylate and Lambda-Cyhalothrin in wine sample by using sodium dodecylsulfate doped polypyrrole SPME fiber. Pyrrole monomer was electrochemically polymerized on a stainless steel wire in laboratory conditions in virtue of diminishing the cost and enhancing the analyte retention on its surface to exert better selectivity and hence the developed polymerized surface could offer to analyst to exploit it as a fiber in headspace SPME analysis. The parameters, mainly, adsorption temperature and time, desorption temperature, stirring rate and salt amount were optimized to be as 70 • C and 45 min, 200 • C, 600 rpm and 10 g L −1 , respectively. Limit of detection was estimated in the range of 0.073-1.659 ng mL −1 for the pesticides studied. The developed method was applied in to red wine sample with acceptable recovery values (92-107%) which were obtained for these selected pesticides.

Electrochimica Acta, 2015

Highlights  The electrode is deposited cycling the potential or pulsed potential technique  PtN... more Highlights  The electrode is deposited cycling the potential or pulsed potential technique  PtNPs/MoOx/GCE shows superior catalytic effect towards to ORR  The surface is characterized with XPS, SEM, EIS and cyclic voltammetry.  The higher catalytic activity was obtained in the pulsed electrodeposition process Abstract 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 2and PtCl 4 2either 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 A C C E P T E D M A N U S C R I P T 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