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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Influence of soft segment structure, hydrogen bonding, and diisocyanate symmetry on morphology and properties of segmented thermoplastic polyurethanes and polyureas(Tubitak Scientific & Technological Research Council Turkey, 2023) Department of Chemistry; Yılgör, Emel; Yılgör, İskender; Department of Chemistry; College of SciencesA comprehensive review of the structure-morphology-property relations in segmented thermoplastic polyurethanes and polyureas (TPU) is provided. Special emphasis is given to the influence of the soft segment structure, polarity, and molecular weight, diisocyanate symmetry and the nature, extent, and strength of hydrogen bonding on the morphology and thermal and mechanical properties of TPUs. Experimental results obtained on composition-dependent TPU morphology and properties by various techniques were also compared by the morphology profiles generated by computational methods such as quantum mechanical calculations and molecular dynamics simulations.Publication Metadata only Electrochemical CO2 reduction to gaseous methane and carbon monoxide using plasma-synthesized copper nanowires(Springer, 2023) Butt, Faaz Ahmed; Alshahrani, Thamraa; Awan, Zahoor Ul Hussain; Christy, Maria; Khan, Firoz; Alanazi, Abdulaziz M.; Department of Chemistry; Ünal, Uğur; Department of Chemistry; College of SciencesThere is a growing interest among environmental researchers to synthesize a sustainable catalyst for CO2 conversion process. Copper and modified copper offer a wide window for such catalysts. In this study, we report the use of plasma-treated copper/copper oxide nanowires for electrochemical CO2 reduction for the first time. Plasma-treated Cu nanowires (CuO-P NWs) were comparatively evaluated with bulk copper surface in CO2 saturated test solutions, namely, KHCO3, KCl, and NaCl, with 0.1 and 1 M concentrations. CuO-P NWs demonstrate 50% increase in selectivity towards CO2 reduced gaseous products (CO and CH4) at a higher applied potential of - 1.1 V vs reversible hydrogen electrode. This increased selectivity is associated with decreased binding energy of the intermediate species on plasma-treated nanowires compared to bulk surface. Both CO and CH4 were the main products detected in the gaseous state, and CO is suggested as the main intermediate species. The effects of different cations and anions and their concentrations in the solutions were also analyzed. It was observed that dilute solutions in 0.1 M are optimal for electrochemical CO2 reduction (ECO2R) and that hydration energy of cations plays a significant role in ECO2R selectivity, while hydrogen evolution reaction was the competing reaction.Publication Metadata only Probing water adsorption characteristics of Pt step-edge decorated CU (211) surface(Elsevier, 2024) Department of Chemistry; Mohammadpour, Amin; Kaya, Sarp; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM); College of Sciences; Graduate School of Sciences and EngineeringThe surface structure and atomic composition can affect the adsorption characteristics of water on metal surfaces. In this study, we investigated the adsorption of water on Cu(211) stepped surfaces decorated with Pt by a combination of infrared reflection absorption spectroscopy (IRRAS) and temperature -programmed desorption (TPD) studies. We have observed that step sites of Cu can increase the strength of the binding of water molecules to the surface and facilitate water partial dissociation and the formation of OH groups on the surface. Step decoration by Pt can change the water adsorption characteristics and eliminate the water dissociation. Water adsorbs molecularly on the fully Pt -decorated steps of the Cu(211) surface. Molecular water and OH adsorbed on Cu(211), which can make a chain structure, are disrupted with Pt atoms.Publication Metadata only Using Auger transitions as a route to determine the oxidation state of copper in high-pressure electron spectroscopy(Elsevier, 2024) Soldemo, Markus; Garcia-Martinez, Fernando; Goodwin, Christopher M.; Loemker, Patrick; Shipilin, Mikhail; Nilsson, Anders; Amann, Peter; Weissenrieder, Jonas; Department of Chemistry; Kaya, Sarp; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM); College of SciencesAccurate discrimination between metallic copper (Cu0) and cuprous oxide (Cu2O, Cu+) in electron spectroscopy commonly relies on the Auger electron spectroscopy (AES) Cu L3M4,5M4,5 transitions, as the X-ray photoelectron spectroscopy (XPS) Cu core-levels do not provide large enough binding energy shifts. The kinetic energy of the AES Cu L3M4,5M4,5 electrons is 917 eV, which leaves the AES electron susceptible for efficient scattering in the gas phase and attenuation of the signal above near-ambient pressure conditions. To study copper-based materials at higher pressures, e.g., the active state of a catalyst, Auger transitions providing electrons with higher kinetic energies are needed. This study focuses on AES transitions involving the Cu K-shell (1s electrons) that exhibit discernible kinetic energy shifts between the oxidation states of Cu. It is shown that the AES Cu KL2M4,5 transition, with kinetic energy of 7936 eV, provides a large enough kinetic energy shift between metallic copper and Cu2O. AES signal is demonstrated in an ambient of 150 mbar CO2.Publication Metadata only Enhancement in CO selectivity by modification of ZnO with CuxO for electrochemical reduction of CO2(Wiley-V C H Verlag Gmbh, 2023) Department of Chemistry; Yusufoğlu, Muhammed; Tafazoli, Saeede; Balkan, Timuçin; Kaya, Sarp; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of SciencesThe electrochemical reduction reaction of carbon dioxide (CO2RR) has garnered significant attention due to its potential for the formation of carbon monoxide, which has industrial relevance. Herein, an oxide-derived Cu-Zn electrocatalyst with an optimized CuxO layer that shows high selectivity toward CO with a faradic efficiency of 75% at a low overpotential (-0.8 V vs reversible hydrogen electrode) is reported. Various structural characterizations and activity tests are conducted to understand the origin of this improvement depending on the CuxO amount. Electrochemical surface area and electrochemical impedance spectroscopy measurements suggest that the addition of CuxO increases double-layer capacitance and decreases charge transfer resistance. Scanning electron microscopy images indicate that the electrodes undergo a severe reconstruction process, which is further confirmed by X-ray diffraction that shows the formation of CuZn4 alloy during the reduction reaction. Furthermore, X-ray photoelectron spectroscopy depth profile analysis shows that after CO2RR at -0.8 V, the Cu/Zn ratio is higher than that after -1.2 V, which suggests that applied potential plays a significant role in the reconstruction process and hence the difference in selectivity. The presence of copper in the surface layer has a significant impact on the improvement of selectivity toward CO.Publication Metadata only High temperature thermoelectric properties of the type-I clathrate BA(8)NI(X)GE46(-X-Y)square(Y)(Institute of Physics (IOP) Publishing, 2014) Candolfi, Christophe; Örmeci, Alim; Baitinger, Michael; Oeschler, Niels; Steglich, Frank; Grin, Yu; Department of Chemistry; Aydemir, Umut; Faculty Member; Department of Chemistry; College of Sciences; 58403Polycrystalline samples of the type-I clathrate Ba8NixGe46-x-y square(y) were synthesized for 0.2 <= x <= 3.5 by melt quenching and for 3.5 < x <= 6.0 by melting with subsequent annealing at 700 degrees C. The maximum Ni content in the clathrate framework at this temperature was found to be x approximate to 4.2 atoms per unit cell. Thermoelectric and thermodynamic properties of the type-I clathrate were investigated from 300 to 700 K by means of electrical resistivity, thermopower, thermal conductivity and specific heat measurements. As the Ni content increases, the electronic properties gradually evolve from a metallic character (x < 3.5) towards a highly doped semiconducting state (x >= 3.5). Below x approximate to 4.0 transport is dominated by electrons, while further addition of Ni (x approximate to 4.2) switches the electrical conduction to p-type. Maximum value of the dimensionless thermoelectric figure of merit ZT approximate to 0.2 was achieved at 500K and 650K for x approximate to 2.0 and x approximate to 3.8, respectively.Publication Metadata only Nanoparticle based induction heating at low magnitudes of magnetic field strengths for breast cancer therapy(Elsevier, 2019) Zuvin, Merve; Koçak, Muhammed; Akkoç, Yunus; Kutlu, Özlem; Gözüaçık, Devrim; Koşar, Ali; N/A; Department of Chemistry; Ünal, Özlem; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178902Magnetic hyperthermia has received much attention during the last decade due to its implementation in cancer treatment. Recently, functionalized superparamagnetic iron oxide nanoparticles (SPION) emerged as a strong alternative adjuvant treatment approach, which complements conventional methods such as chemotherapy. In this study, we demonstrate the anticancer effect of Poly(acrylic acid)-coated, anti-HER2-tagged SPIONs on breast cancer cells using a low magnetic field strength of 0.8 kAm(-1), which is significantly lower compared to the literature, with a frequency of 400 kHz. Specificity was achieved via anti-HER2 antibody attachment to nanoparticles. HER2-positive SKBR3 and MDA-MB-453 cell lines internalized the nanoparticles successfully. These nanoparticles, which were not toxic to these cell lines, led to a prominent decrease in cell proliferation and survival in MDA-MB-453 cells when subjected to hyperthermia. Therefore, the hyperthermia-targeted SPION approach could be developed as a potential cancer treatment approach against breast cancer and possible other cancer types.Publication Metadata only Heteroarm H-shaped terpolymers through click reaction(Wiley, 2007) Güngör, Eda; Cote, Gülay; Erdoğan, Tuba; Durmaz, Hakan; Hızal, Gürkan; Tunca, Ümit; Department of Chemistry; Demirel, Adem Levent; Faculty Member; Department of Chemistry; College of Sciences; 6568Heteroarm H-shaped terpolymers, (polystyrene)(poly(methyl methacrylate))poly(tert-butyl acrylate)-(polystyrene)(poly(methyl methaerylate)), (PS)(PMMA)-PtBA-(PMMA)(PS), and, (PS)(PMMA)-poly(ethylene glycol)(PEG)-(PMMA)(PS), through click reaction strategy between PS-PMMA copolymer (as side chains) with an alkyne functional group at the junction point and diazide end-functionalized PtBA or PEG (as a main chain). PS-PMMA with alkyne functional group was prepared by sequential living radical polymerizations such as the nitroxide mediated (NMP) and the metal mediated-living radical polymerization (ATRP) routes. The obtained H-shaped polymers were characterized by using H-1-NMR, GPC, DSC, and AFM measurements. (c) 2006 Wiley Periodicals, Inc.Publication Metadata only Highly fibrous semi-synthetic hydrogels to characterize cell motility(Springer, 2015) N/A; Department of Chemistry; Akalın, Özge Begüm; Bayraktar, Halil; Master Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 201764Publication Metadata only Controlling oxygen reduction reaction activities of Ag@Pt core-shell nanoparticles via tuning of ag in the surface layer(Wiley-VCH, 2023) Savaci, Umut; Turan, Servet; N/A; N/A; N/A; Department of Chemistry; Department of Chemistry; Aksoy, Dilan; Karakaya, Cüneyt; Balkan, Timuçin; Metin, Önder; Kaya, Sarp; PhD Student; PhD Student; Other; Faculty Member; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; College of Sciences; College of Sciences; N/A; N/A; N/A; 46962; 116541Herein, the effect of Pt shell thickness and Ag content in the surface layer on the oxygen reduction reaction activities of Ag@Pt core@shell nanoparticles (NPs) is discussed. Ag@Pt NPs are synthesized via the seeded-growth method, where colloidal Ag NPs are first synthesized and used as seeds for the growth of Pt. Electrochemical activity measurements in alkaline media show a remarkable dependency between the Ag content in the shell and the oxygen reduction reaction (ORR) activity, where the overpotentials required for -1.0 mA cm(-2) drop gradually, that is, 0.72, 0.77, and 0.80 V-RHE for Ag@Pt-25, Ag@Pt-35, and Ag@Pt-45, respectively. Tafel analysis also confirms this dependency with 73.5 mV dec(-1) for Ag@Pt-25, 71.3 mV dec(-1) for Ag@Pt-35, and 68.8 mV dec(-1) for Ag@Pt-45. A combination of the high-resolution transmission electron microscope, X-ray photoelectron spectroscopy, and X-Ray diffraction analysis shows an increase of the Pt shell thickness. It is shown that the absence of Pt-H adsorption/desorption peaks in cyclic voltammetry of Ag@Pt NPs is correlated with Ag in the surface layer, which plays an important role in the ORR activity due to the blockage of Pt(111) terrace sites. Rate-limiting first-electron transfer to oxygen is facilitated by decreasing Ag amount at the surface.