Department of Chemistry
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Browsing Department of Chemistry by Type "Conference Paper"
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Item Open Access Adsorption behavior of radionuclides, 137Cs and 140Ba, onto solid humic acid(Springer, 2011) Çelebi, O.; Erten, Hasan N.In this research, the adsorption behaviors of two important fission product radionuclides (137Cs and 133Ba) onto sodium form of insolubilized humic acid (INaA) were investigated as a function of time, cation concentration and temperature, utilizing radiotracer method. The resulting data was fitted well to the Freundlich and Dubinin-Radushkevich (D-R) isotherms. Thermodynamic constants such as; free energy (ΔGads), enthalpy (ΔHads), entropy (ΔSads) of adsorption were determined. Temperature change didn't effect sorption processes significantly. Best fitting kinetic models were found for a better understanding of adsorption mechanisms. It was found that Ba2+ was adsorbed five times more than Cs+ onto structurally modified humic acid and kinetic studies indicated that adsorption behaviors of both ions obey the pseudo second order rate law. The effect of pH changes on adsorption was also examined and optimum pH range was found in the range of pH 6-8. FTIR and solid state carbon nmr (13CNMR) spectroscopic techniques were used to understand the structural changes during insolubilization process. Quantitative determination of adsorption sites was carried out using potentiometric titration method and the resulting data was treated by using appropriate Gran functions.Item Open Access Analysis of errors in zero-free-parameter modeling approach to predict the voltage of electrochemical energy storage systems under arbitrary load(Electrochemical Society, 2017) Ulgut, Burak; Uzundal, Can Berk; Özdemir, ElifIn a recently published article (J. Electrochem. Soc. 164 (2017) A1274-A1280), we described a new method to predict the voltage response of electrochemical energy storage systems during arbitrary load profiles. Our work shows that the impedance spectrum can be employed in the frequency domain in order to ultimately calculate the time domain behavior of the electrochemical energy storage system. The big advantage of this method is the fact that there are no free parameters and fits throughout. The present work deals with the sources of error in the above-mentioned prediction approach and looks for the effects of the various sources of error. The current analysis concludes that two big contributors to the overall error are the inaccuracies in the DC part of the prediction and the non-linearities that are not modeled by a linear impedance spectrum. Discussions are also made regarding ways to improve the performance of the modeling approach the most and where future work is going to be looking to improve.Item Open Access Anisotropic actuation in salty agarose gel actuators(Springer, 2023-08-01) Tootoonchian, Pedram; Bahçeci, Levent; Baytekin, BilgeWhen hydrogels that can reversibly dehydrate/rehydrate are physically combined with a constant water supply, the cycles can be controlled by on/off states and the positions of an external light source. The shrinking upon dehydration upon illumination causes bending towards the light source, and rehydration in the light-off state restores the initial shape. This simple material feedback mechanism mimics the self-regulating heliotropism (sun tracking) and nyctinasty (leaf opening) movements of plants. In this work, we show the effect of some common salts on the bending behavior of actuators entirely made of hydrogel. The ‘salty’ actuators exhibit different motion kinetics regarding the unique chemical characteristics of each ion. We display that this chemistry of ions also enables us to program the kinetics in a single actuator using the differences in evaporation/diffusion rate of water in the salty gels. This programmability of the motion in a hydrogel actuator with the inclusion of salts can be used to achieve complex behavior observed in living organisms straightforwardly.Item Open Access Band alignment issues in metal/dielectric stacks: a combined photoemission and inverse photoemission study of the HfO 2/Pt and HfO 2/Hf systems(Electrochemical Society, 2004) Sayan, S.; Bartynski, R.A.; Robertson J.; Suehle, J. S.; Vogel, E.; Nguyen, N. V.; Ehrstein, J.; Kopanski, J. J.; Süzer, Şefik; Holl, M. B.; Garfunkel, E.We have studied the HfO 2/Hf and HfO 2/Pt systems by photoemission and inverse photoemission spectroscopies. It is found that the "effective workfunction" of metals in multilayer structures are different than their vacuum workfunctions and are modified by their interface dipoles at the metal/high-k interface. The effective workfunction of Hf is 4.4 eV whereas that of Pt is 5.3 eV, within the range of acceptable values for PMOS and NMOS respectively.Item Open Access Controlled optical transition rates in nanodroplets(IEEE, 2000) Özçelik, SerdarThe time-resolved fluorescence measurements of 3,3′-diethyl-5,5′-dichloro-9-phenylthiacarbocyanine (DDPT) in bulk solvents and methanol-in-oil reverse micellar systems is presented which include nano-sized methanol droplets stabilized with anionic surfactant aerosol-OT (AOT) in n-heptane, at room temperature. Relative fluorescence intensities of DDPT increase with a factor of 16 in m/o reverse micelles in comparison to those in bulk methanol. The radiative and nonradiative rate constants decreases in methanol dispersions, indicating that internal motions of DDPT in the droplets is reduced due to strong electrostatic interactions between the positively charged DDPT and the negatively charged sulfonate head-groups of AOT.Item Open Access Controlling the surface dispersion of BaO domains on NOx storage materials via TiO2 anchoring sites(ACS, 2010) Andonova, Stanislava M.; Şentürk, Göksu S.; Özensoy, EmrahIn an attempt to control the surface dispersion and the mobility of BaO domains on NOx storage materials, TiO2/TiOx anchoring sites were introduced on/inside the conventional γ-Al2O3 support matrix. BaO/TiO2/γ-Al2O3 ternary oxide materials were synthesized via two different sol-gel preparation techniques, with varying surface compositions and morphologies. The synthesized NOx storage materials were studied via XRD, Raman spectroscopy, BET surface area analysis, TPD, XPS, SEM, EDX-mapping and in situ FTIR spectroscopy of adsorbed NO2. NOx uptake properties of the BaO/TiO2/γ-Al2O3 materials were found to be strongly influenced by the morphology and the surface structure of the TiO2/TiOx domains. The presence of Ti4+ surface sites provide additional NOx adsorption sites which can store NOx predominantly in the form of bridged/bidentate nitrates. An improved Ba surface dispersion was observed for the BaO/TiO2/γ-Al2O3 materials synthesized via the co-precipitation of alkoxide precursors which was found to originate mostly from the increased fraction of accessible TiO2/TiOx sites on the surface. These TiO2/TiOx sites function as strong anchoring sites for surface BaO domains and can be tailored to enhance surface dispersion of BaO. TPD experiments suggested the presence of at least two different types of NOx species adsorbed on the TiO2/TiOx sites, with distinctively different thermal stabilities. The relative stability of the NOx species adsorbed on the BaO/TiO2/γ-Al2O3 system was found to increase in the following order: NO+/N2O3 on alumina < nitrates on alumina < surface nitrates on BaO < bridged/bidentate nitrates on large/isolated TiO2 clusters < bulk nitrates on BaO on alumina surface and bridged/bidentate nitrates on small TiO2 crystallites homogenously distributed on the surface < bulk nitrates on the BaO sites located on the TiO2 domains.Item Open Access Electrical and chemical characterization of chemically passivated silicon surfaces(IEEE, 2008) Chhabra, B.; Süzer, Şefik; Opila, R. L.; Honsberg, C. B.The surface composition of chemically passivated silicon substrates is investigated using XPS and FTIR techniques. The samples are passivated with methanol, quinhydrone-methanol and iodine-methanol solution after HF treatment. The minority carrier lifetimes of these chemically passivated silicon substrates are also measured. Quinhydrone-methanol solution provides a chemically inert surface and a considerably longer minority carrier lifetime.Item Open Access High-quality white light generation using dually hybridized nanocrystals and conjugated polymers(IEEE, 2007) Nizamoğlu, Sedat; Özel, Tuncay; Mutlugun, Evren; Huyal, Ilkem Ozge; Sarı, Emre; Tian, N.; Holder, E.; Demir, Hilmi VolkanItem Open Access Increased quantum efficiency and reduced red-shift in polymer nanoparticle luminophors(IEEE, 2008-11) Huyal, İlkem Özge; Özel, Tuncay; Tuncel, Dönüş; Demir, Hilmi VolkanIn this paper, using a polyfluorene derivative, increased fluorescence quantum efficiency and reduced red-shift in the film form of polymer nanoparticle luminophors is achieved, when compared to directly spin coated polymer thin films.Item Open Access Joint design and fabrication for multi-material soft/hybrid robots(IEEE, 2019-04) Aygül, Cern; Kwiczak-Yiğitbaşı, Joanna; Baytekin, Bilge; Özcan, OnurThe premises of safer interactions with surroundings and the higher adaptability to its environment make soft robotics a very interesting research field. Some robots try to achieve these feats using soft materials in their designs whereas some achieve behavioral softness through compliant use of hard materials. In this work, we present soft/hybrid robot leg designs that utilize elastomers as leg materials but hard DC motors as actuators. Two different leg designs that would convert the rotational motion of the DC motors to a foot trajectory are proposed. The different leg designs are kinematically identical; however, the hourglass design utilizes geometrical modifications to differentiate joint locations, whereas the composite design uses materials with different Young's Moduli without geometrical effects to create joints. In order to fabricate the composite design, a new method is developed involving 3D printed molds with removable joint pieces and a two-step molding process. Both of the legs are fabricated and simulations and experiments are run to compare their performances. Both mechanisms achieve a good foot trajectory, however the hourglass joint experiences higher mechanical stress during operation, which might lead to earlier failure especially under high loads. Such multi-material structures made out of elastomers can be utilized in miniature robots or mechanisms of similar size in which absolute joint locations are needed and continuum robotic limbs are not preferred.Item Open Access Photonic devices and systems embedded with nanocyrstals(SPIE, 2006) Demir, Hilmi Volkan; Soğancı, Ibrahim Murat; Mutlugun, Evren; Tek, Sümeyra; Huyal, Ilkem OzgeWe review our research work on the development of photonic devices and systems embedded with nanocyrstals for new functionality within EU Phoremost Network of Excellence on nanophotonics. Here we report on CdSe/ZnS nanocrystalbased hybrid optoelectronic devices and systems used for scintillation to enhance optical detection and imaging in the ultraviolet range and for optical modulation via electric field dependent optical absorption and photoluminescence in the visible. In our collaboration with DYO, we also present photocatalytic TiO2 nanoparticles incorporated in solgel matrix that are optically activated in the ultraviolet for the purpose of self-cleaning.Item Open Access Radiochronological methods as tools to study environmental pollution(Springer, 2011) Erten, Hasan N.The study of the environmental impact of natural and anthropogenic events forms the essence of environmental pollution considerations. The nature of the polluting species as well as their time distributions are of primary importance with respect to identifying the polluting sources. Sediments are the most frequently used materials in such studies. Sediments act as the ecological memories of the environments of their formation. Besides classical chronological methods, radiochronological methods developed recently gave a big impetus to environmental pollution studies. One of the key radioisotopic technique is to utilize 210Pb, a product of the 235U radioactive series to date the last 200 years of the sediments. A number of supporting indicators are also utilized. One of them being anthropogenic 137Cs which is used as a time-marker. Large amounts of 137Cs radioactivity was released to the environment during 1954-1963, in time of the most intense atmospheric nuclear arms testing and again in 1986 during the Chernobyl nuclear accident. These intense 137s activities form time-markers throughout sediment cores corresponding to their release years. During our studies extending over several years we have used radiochronological methods in dating several sediment cores from Zurich and Constance Lakes in Switzerland from east coast of Spain, Sea of Marmara, from the Black Sea region, Southern coast of Turkey and from North Cyprus. The distribution of several elemental concentrations of importance in pollution considerations along sediment cores were also determined. These studies allowes proposing time frames to pollution events and help inqueries in tracing possible sources of pollution.Item Open Access Sorption of Cs+ and Ba2+ on magnesite(Cambridge University Press, 1998) Shahwan, Talal; Süzer, Şefik; Erten, Hasan N.Sorption behavior of Cs and Ba ions on magnesite was studied using the radiotracer method complemented by X-ray photoelectron spectroscopy. Cs and Ba were used as radiotracers. The sorption of Cs is seen to be temperature dependent, whereas Ba sorption is not much affected by temperature changes. It was found that Freundlich type isotherms provide an adequate description of the sorption process. The magnitude of the free energy of sorption are seen to be within the 8-16 kj/mol range. It can be remarked that the sorption of Cs and Ba on magnesite is a fast process suggesting an ion exchange type mechanism, mainly taking place at the surface of mineral particles.Item Open Access Use of saccharides as solid-state precursors for the synthesis of carbon nanotubes(Materials Research Society, 2008) Küçükkayan, Gökçe; Kayacan, Serim; Baykal, Beril; Bengu, ErmanSaccharides, ranging from simple table sugar (sucrose) to lactulose were successfully used as solid-state precursors for the synthesis of multi-walled carbon nanotubes (MWCNT). Dehydrated saccharide residues mixed with catalyst powders were subjected to pyrolysis at high temperatures (up to 1300°C) under flowing Argon atmosphere. Pyrolysis products were investigated using TEM, SEM, Raman spectroscopy and EDS. Images taken using the S/TEM and bright field mode of TEM showed the presence of helical multi-walled carbon nanotube (H-MWCNT) and regular MWCNT formation. More than two or three catalyst particles were observed to be present inside the hollow core of some of the nanotubes synthesized, suggesting a high level of capillary activity inside the tubes during synthesis. © 2008 Materials Research Society.Item Open Access Wavelet merged multi-resolution super-pixels and their applications on fluorescent MSC images(IEEE, 2015) Yorulmaz, Onur; Oğuz, Oğuzhan; Akhan, Ece; Tuncel, Dönüş; Atalay, R. Ç.; Çetin, A. EnisA new multi-resolution super-pixel based algorithm is proposed to track cell size, count and motion in Mesenchymal Stem Cells (MSCs) images. Multi-resolution super-pixels are obtained by placing varying density seeds on the image. The density of the seeds are determined according to the local high frequency components of the MSCs image. In this way a multi-resolution super-pixels decomposition of the image is obtained. A second contribution of the paper is novel decision rule for merging similar neighboring super-pixels. An algorithm based on well known wavelet decomposition is developed and applied to the histograms of neighboring super pixels to exploit similarity. The proposed algorithm is experimentally shown to be successful in segmenting and tracking cells in MSCs images.Item Open Access White light generation with azide functionalized polyfluorene hybridized on near-UV light emitting diode(OSA, 2007) Hüyal, İlkem Özge; Özel, Tuncay; Nizamoğlu, Sedat; Koldemir, Ünsal; Tuncel, Dönüş; Demir, Hilmi VolkanWe present white light generation using poly[(9,9-dihexylfluorene)-co-alt- (9,9-bis-(6- azidohexyl)fluorene] (PFA) for the first time. Hybridizing PFA on near-UV LED, we demonstrate high color rendering index up to 91.0.