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    A comparative study of electrochemical methods on Pt-Ru DMFC anode catalysts: The effect of Ru addition
    (PERGAMON-ELSEVIER SCIENCE LTD, 2013) Sahin, Ozlem; Kivrak, Hilal
    In the present study comparative electrochemical study of methanol electro-oxidation reaction, the effect of ruthenium addition and experimental parameters on methanol electro-oxidation reaction at high performance carbon supported Pt and Pt-Ru catalysts have been studied by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in H2SO4 (0.05-2.00 M) + CH3OH (0.01-4.00 M) at 20-70 degrees C. Tafel plots for the methanol oxidation reaction on Pt and Pt-Ru catalysts show reasonably well-defined linear region with the slopes of 128-174 mV dec(-1)(alpha = 0.34-0.46). The activation energies from Arrhenius plots have been found as 39.06-50.65 kJ mol(-1). As a result, methanol oxidation is enhanced by the addition of ruthenium. Furthermore, Pt-Ru (25:1) catalyst shows best electro-catalytic activity, higher resistance to CO, and better long term stability compared to Pt-Ru (3:1), Pt-Ru (1:1), and Pt. Finally, the EIS measurements on Pt-Ru (25:1) catalyst reveals that methanol electro-oxidation reaction consists of two process: methanol dehydrogenation step at low potentials (<700 mV) and the oxidation removal of COads by OHads at higher potentials (>700 mV). Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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    A complementary study on novel PdAuCo catalysts: Synthesis, characterization, direct formic acid fuel cell application, and exergy analysis
    (PERGAMON-ELSEVIER SCIENCE LTD, 2018) Kivrak, Hilal; Atbas, Dilan; Alal, Orhan; Cogenli, M. Selim; Bayrakceken, Ayse; Mert, Suha Orcun; Sahin, Ozlem
    At present, Pd containing (10-40 wt%) multiwall carbon nanotube (MWCNT) supported Pd monometallic, Pd:Au bimetallic, and PdAuCo trimetallic catalysts are prepared via NaBH4 reduction method to examine their formic acid electrooxidation activities and direct formic acid fuel cell performances (DFAFCs) when used as anode catalysts. These catalysts are characterized by advanced analytical techniques as N-2 adsorption and desorption, XRD, SAXS, SEM-EDX, and TEM. Electronic state of Pd changes by the addition of Au and Co. Moreover, formic acid electrooxidation activities of these catalysts measured by CV indicates that particle size changes in wide range play a major role in the formic acid electrochemical oxidation activity, ascribed the strong structure sensitivity of formic acid electrooxidation reaction. PdAuCo (80:10:10)/MWCNT catalyst displays the most significant current density increase. On the other hand, lower CO stripping peak potential obtained for PdAuCo (80:10:10)/MWCNT catalyst, attributed to the awakening of the Pd-adsorbate bond strength down to its optimum value, which favors higher electrochemical activity. DFAFCs performance tests and exergy analysis reveal that fuel cell performances increase with the addition of Au and Co which can be attributed to synergetic effect. Furthermore, temperature strongly influences the performance of formic acid fuel cell. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    An ethanol electrooxidation study on carbon-supported Pt-Ru nanoparticles for direct ethanol fuel cells
    (TAYLOR & FRANCIS INC, 2016) Sahin, Ozlem; Duzenli, Derya; Kivrak, Hilal
    Carbon supported Pt-Ru catalysts were prepared at varying Pt:Ru ratios by polyol method. The crystallite sizes of these catalysts were determined by X-ray diffraction technique. The specific surface areas of these catalysts were also defined by Brunauer-Emmett-Teller technique. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements were conducted on these carbon supported Pt-Ru catalysts to investigate the effect of ruthenium on the ethanol electrooxidation kinetics. Results indicated that Pt-Ru (25:1) catalyst showed the best ethanol electrooxidation activity. In conclusion, ethanol electrooxidation mechanism was proposed.
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    Facile and Rapid Synthesis of Microwave Assisted Pd Nanoparticles as Non-Enzymatic Hydrogen Peroxide Sensor
    (ESG, 2017) Sahin, Ozlem; Kivrak, Hilal; Kivrak, Arif; Kazici, Hilal Celik; Alal, Orhan; Atbas, Dilan
    Carbon supported Pd catalyst was prepared with microwave-assisted polyol method (M-Pd@C) and investigated sensing activity for non-enzymatic hydrogen peroxide (H2O2). Moreover, M-Pd@C and Pd@C catalyst which synthesized via polyol method (P-Pd@C) were compared to each other in terms of electrocatalytic activity. X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate structural and morphological properties of these catalysts. Furthermore, electrochemical measurements were performed via cyclic voltammetry (CV), chronoamperometry (CA) techniques. CV results exhibited that M-Pd/C catalyst showed perfect electrocatalytic activity in terms of reduction of H2O2. M-Pd/C catalyst showed a fast response of less than 7 s with a linear range of 5.0x10(-3)-11.0 mM and a relatively low detection limit of 1.2 mu M amperometric response. M-Pd/C catalyst exhibited great selectivity for detecting H2O2 in the existence of several hindering species such as uric acid and ascorbic acid.
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    Facile and Rapid Synthesis of Microwave Assisted Pd Nanoparticles as Non-Enzymatic Hydrogen Peroxide Sensor (vol 12, pg 762, 2017)
    (ESG, 2018) Sahin, Ozlem; Kivrak, Hilal; Kivrak, Arif; Kazici, Hilal Celik; Alal, Orhan; Atbas, Dilan
    [Abstract not Available]
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    Methanol Electrooxidation Study on Mesoporous Silica Supported Pt-Co Direct Methanol Fuel Cell Anode
    (WALTER DE GRUYTER GMBH, 2014) Kivrak, Hilal; Can, Mukaddes; Duru, Hatice; Sahin, Ozlem
    At present, Pt was impregnated by incipient wetness impregnation method on Co-doped SBA-15 catalysts prepared by sol-gel method at different weight percentages of Co to investigate the effect of Pt: Co ratio on methanol electrooxidation reaction (MOR). Cyclic voltammetry (CV), chronoamperometry (CA), and linear sweep voltammetry (LSV) techniques were employed to examine the MOR activities, poisoning capacity, and stability of these Pt/SBA-15 and Pt-Co/SBA-15 catalysts. Co presence in the platinum structure enhances the electrocatalytic activity of MOR, due to oxidation of Co at relatively low positive potentials. CV and CA measurements indicated that the most active catalyst was Pt-Co (86:14)/SBA-15 catalyst for MOR. Stability and poisoning measurements revealed that Co presence in the catalyst increases CO poisoning resistance and its stability, in agreement with CV and CA measurements.
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    A phenanthrene-based calix[4]arene as a fluorescent sensor for Cu2+ and F-
    (PERGAMON-ELSEVIER SCIENCE LTD, 2014) Sahin, Ozlem; Akceylan, Ezgi
    A new phenanthrene-based fluorescent calix[4]arene (4) has been synthesized in cone conformation. This compound was examined for its fluorescent properties towards different metal ions (Na+, Li+, Mg2+, Ni2+, Ba2+, Ca2+, Cu2+, Pb2+) and anions (F-, Cl-, Br-, H2PO4-, NO3-, HSO4-, CH3COO-) by fluorescence spectroscopy. The properties of the compound were evaluated and show that it is a fluorescence sensor for Cu2+ and F-. With the addition of Cu2+ and F-, the fluorescence was severely quenched. (C) 2014 Elsevier Ltd. All rights reserved.
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    The role of fluorodeoxyglucose-positron emission tomography/computed tomography in differentiating between benign and malignant adrenal lesions
    (LIPPINCOTT WILLIAMS & WILKINS, 2011) Kara, Pelin Ozcan; Kara, Taylan; Gedik, Gonca Kara; Kara, Fatih; Sahin, Ozlem; Gunay, Emel Ceylan; Sari, Oktay
    Objectives This retrospective study was designed to investigate the clinical role of whole-body positron emission tomography/computed tomography (PET/CT) by using 2[(18)F]fluoro-2-deoxy-D-glucose (FDG), for the evaluation of adrenal lesions and to find the best index to distinguish benign from malignant lesions in various cancer patients. Materials and methods A total of 81 patients (55 male and 26 female, age range: 31-81 years, mean: 61.5) who had confirmed primary malignancies (lung cancer in 47 patients, gastrointestinal malignancies in 13 patients, malignant melanoma in one patient, renal cell cancer in three patients, mesothelioma in two patients, breast carcinoma in nine patients, cervical cancer in one patient, ovarian cancer in two patients, pheochromocytoma in one patient, unknown primary in two patients) underwent PET/CT examinations for cancer screening, staging, restaging, and detection of suspected recurrence. Of the 81 patients, 104 adrenal lesions (34 benign and 70 malignant adrenal lesions) were shown by CT. On visual analysis of PET/CT imaging, adrenal uptake was based on a three-scale grading system. For final assessment standards of references for adrenal malignant lesions was based on biopsy (n=2), interval growth, or reduction after chemotherapy. An adrenal lesion, which remained unchanged on clinical and imaging follow-up of at least 7 months (mean follow-up time 19.31 months +/- 6.46, range 7-30 months), was decided as a benign lesion. Results In adrenal malignant lesions maximum standardized uptake value (SUV(max)) (8.82 +/- 4.47) was higher than that of adrenal benign lesions (3.02 +/- 1.15, P<0.0001). In the differentiation of adrenal benign and malignant lesions, a CT threshold of 10 Hounsfield units corresponded to a sensitivity of 64.7%, specificity of 98.6%, and accuracy of 87.5%. An SUV(max) cut-off value of 2.5 corresponded to a sensitivity of 100%, specificity of 38.2%, and accuracy of 80%. An SUV(max) cut-off value of 4.2 corresponded to a sensitivity of 88.6%, specificity of 88.2%, and accuracy of 88.5%. The ratio of tumor SUV(max) to liver SUV(mean) was 3.61 +/- 1.77 for adrenal malignant lesions whereas it was 1.20 +/- 0.38 for adrenal benign lesions (P<0.0001). T/L SUV ratio cut-off value of 1.8 corresponded to a sensitivity of 87%, specificity of 91%, and accuracy of 88.5%. T/L SUV ratio cut-off value of 1.68 corresponded to a sensitivity of 90%, specificity of 91.1%, and accuracy of 90.4%. Conclusion 2-[(18)F]fluoro-2-deoxy-D-glucose-PET/CT improves the diagnostic accuracy in the differentiation of benign from malignant adrenal lesions in various cancer patients. Combined information obtained from PET/CT (SUV(max) T/L SUV ratio, visual analysis) and unenhanced CT (size, Hounsfield units measurement) is recommended for better differentiation. Nucl Med Commun 32:106-112 (C) 2011 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins. Nuclear Medicine Communications 2011, 32:106-112
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    Synthesis and spectral properties of pyrene based calix[4]arene
    (ELSEVIER, 2013) Sahin, Ozlem
    A new pyrene-based calix[4]arene was synthesized. This compound (4) was examined for its fluorescent properties towards different metal ions (Mg-2+,Mg- Ni2+, Ba2+, Ca2+, Cu2+, Pb2+, Zn2+) and anions (F-, Cl-, Br-, H2PO4-, NO3-, HSO4-, CH3COO-) by UV, NMR and fluorescence spectroscopy. Fluorescence spectroscopy demonstrated that 4 exhibited high affinity for Cu2+ and low affinity for Pb2+, Mg2+, F-. Quenching constant and stability constants for complexation of 4 with Cu2+ and F- have been determined according to literature. (C) 2013 Elsevier B.V. All rights reserved.