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Publication Metadata only Transformation of reduced graphene aerogel-supported atomically dispersed iridium into stable clusters approximated as Ir-6 during ethylene hydrogenation catalysis(Elsevier, 2022) Zhao, Yuxin; Hoffman, Adam S.; Gates, Bruce C.; Bare, Simon R.; Department of Chemistry; Department of Chemical and Biological Engineering; N/A; N/A; N/A; Ünal, Uğur; Uzun, Alper; Öztulum, Samira Fatma Kurtoğlu; Yalçın, Kaan; Çağlayan, Hatice Pelin; Faculty Member; Faculty Member; PhD Student; Master Student; Master Student; Department of Chemistry; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Sciences; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 42079; 59917; 384798; N/A; N/ATransformation of atomically dispersed reduced graphene aerogel (rGA)-supported complexes, Ir-I(C2H4)(2)(+), with an iridium loading of 9.9 wt%, to form low-nuclearity clusters was investigated during ethylene hydrogenation catalysis. Continuous-scan X-ray absorption spectra demonstrate the formation of clusters well approximated as Ir-4 during reaction at 100 degrees C in flowing equimolar ethylene and H-2. The Ir-4 clusters transformed into clusters well approximated as Ir 6 when the feed molar ratio was switched to H-2: C2H4 = 2 and remained stable in pure H-2 at 100 degrees C. Catalyst performance data show that hydrogenation activity increased with metal nuclearity in the order of atomically dispersed iridium/rGA << Ir-4/rGA < Ir-6/ rGA. Continuous scan X-ray absorption data, complemented with aberration-corrected scanning transmission electron microscopy images, demonstrate that the supported clusters approximated as Ir-6 are stable even in H-2 at atmospheric pressure and 100 degrees C. These supported iridium clusters are among the ones having the highest metal loadings reported for a supported metal cluster catalyst.Publication Metadata only The entry of molecular species into the lattice of an electroactive polymer during its dissolution(Elsevier Science Bv, 2006) Morton Blake, D. A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Molecular details obtained from quantum chemical DFT calculations on 3-methylthiophene oligomers are used in a molecular dynamics (MD) investigation of the solution-interface region of the soluble polymer poly(3-alkylthiophene) in its oxidized (electroactive) form. The MD shows that the presence of the solvent interface results in conformational changes in the polymer main chains in that region from all-trans to largely cis. The entry of BF4- ions and solvent molecules (chloroform) across the interface from the solvent to the positively charged polymer is anisotropic (particularly for the ions), entry occurring most readily along the direction of the main chains. Both BF4- solute ions and CHCl3 solvent molecules occupy specific sites in the polymer, but those of the BF4- ions are the better defined. A temperature study of the incursion of the two species into the polymer shows that the entry of the ions has a small activation energy.Publication Metadata only Influence of kosmotrope and chaotrope salts on water structural relaxation(American Chemical Society (ACS), 2020) Luo, Peng; Zhai, Yanqin; Mamontov, Eugene; Xu, Guangyong; Faraone, Antonio; Department of Chemical and Biological Engineering; Şenses, Erkan; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 280298The structural relaxation in water solutions of kosmotrope (structure maker) and chaotrope (structure breaker) salts, namely sodium chloride, potassium chloride, and cesium chloride, were studied through quasielastic neutron scattering measurements. We found that the collective dynamics relaxation time at the structure factor peak obtained using heavy water solutions shows a distinctively different behavior in the kosmotrope as opposed to the chaotrope solutions, increasing with the salt concentration in the former and decreasing in the latter. In both cases the trends are proportional to the concentration dependence of the relative viscosity of the solutions. These results indicate that kosmotropes and chaotropes influence the solutions viscosity by impacting in opposite ways the hydrogen bond network of water, strengthening it in one case and softening it in the other.Publication Metadata only Enhanced hydrogen evolution by using ternary nanocomposites of mesoporous carbon nitride/black phosphorous/transition metal nanoparticles (m-gcn/bp-m; m = co, ni, and cu) as photocatalysts under visible light: a comparative experimental and theoretical study(Elsevier, 2022) Acar, Eminegul Genc; Yanalak, Gizem; Aslan, Emre; Kilic, Murat; Patır, İmren Hatay; N/A; N/A; Department of Chemistry; Yılmaz, Seda; Metin, Önder; PhD Student; Faculty Member; Department of Chemistry; N/A; N/A; College of Sciences; N/A; N/A; 46962The effect of first-row transition metal nanoparticles as co-catalysts on the activity of mesoporous graphitic carbon nitride (m-gCN) and black phosphorous (BP) heterojunctions (m-gCN/BP) in the photocatalytic hydrogen evolution reaction (HER) is investigated comparatively. Three m-gCN/BP-M (M: Co, Ni, and Cu) ternary nanocomposites were prepared via wetness impregnation and chemical reduction of metal precursors on as-prepared m-gCN/BP binary heterojunctions. The photocatalytic HER activities of m-gCN, m-gCN/BP, m-gCN/BP-Ni, mgCN/BP-Co, and m-gCN/BP-Cu nanocomposites were determined to be 0.233, 0.330, 0.442, 0.326, and 0.223 mmol g-1 h-1, respectively, under visible light illumination. These results revealed that type of transition metal NPs as co-catalysts have considerable effect on the activity of m-gCN/BP heterojunctions in the photocatalytic HER, among which m-gCN/BP-Ni is the best one. The DFT calculations performed on the nanocomposites revealed that m-gCN/BP-Ni possesses the lowest band gap and the highest visible light absorption resulting in the highest photocatalytic activity in HER.Publication Metadata only Low-cost optical assays for point-of-care diagnosis in resource-limited settings(Amer Chemical Soc, 2021) Jiang, Nan; Tansukawat, Natha Dean; Gonzalez-Macia, Laura; Ateş, H. Ceren; Dinçer, Can; Güder, Fırat; Yetişen, Ali K.; Department of Mechanical Engineering; Taşoğlu, Savaş; Faculty Member; Department of Mechanical Engineering; College of Engineering; 291971Readily deployable, low-cost point-of-care medical devices such as lateral flow assays (LFAs), microfluidic paper-based analytical devices (mu PADs), and microfluidic thread-based analytical devices (mu TADs) are urgently needed in resource-poor settings. Governed by the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverability) set by the World Health Organization, these reliable platforms can screen a myriad of chemical and biological analytes including viruses, bacteria, proteins, electrolytes, and narcotics. The Ebola epidemic in 2014 and the ongoing pandemic of SARS-CoV-2 have exemplified the ever-increasing importance of timely diagnostics to limit the spread of diseases. This review provides a comprehensive survey of LFAs, mu PADs, and mu TADs that can be deployed in resource-limited settings. The subsequent commercialization of these technologies will benefit the public health, especially in areas where access to healthcare is limited.Publication Metadata only A comprehensive study on the characteristic spectroscopic features of nitrogen doped graphene(Elsevier, 2019) Ogasawara, Hirohito; N/A; N/A; N/A; Department of Chemistry; Solati, Navid; Mobassem, Sonia; Kahraman, Abdullah; Kaya, Sarp; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Chemistry; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 116541Despite significant methodical improvements in the synthesis of N-doped graphene, there are still unsolved questions regarding the control of content and the configuration of nitrogen species in graphene honeycomb network. A cross-examination of X-ray photoelectron spectroscopy and Raman spectroscopy findings indicates that the nitrogen dopant amount is graphene thicknesses dependent, but the various nitrogen dopant coordination can be obtained on both double- and few-layer graphene. Characteristic defect features (D') appearing in Raman spectra upon N-doping is sensitive to nitrogen dopant coordination, graphitic-pyridinic/nitrilic species and therefore the doping level can be identified. Pyridinic and nitrilic nitrogen as primary species turn graphene to p-type semiconductor after a mild thermal treatment.Publication Metadata only An emerging platform for drug delivery: aerogel based systems(Elsevier, 2014) N/A; Department of Chemical and Biological Engineering; Ülker, Zeynep; Erkey, Can; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; 262388; 29633Over the past few decades, advances in "aerogel science" have provoked an increasing interest for these materials in pharmaceutical sciences for drug delivery applications. Because of their high surface areas, high porosities and open pore structures which can be tuned and controlled by manipulation of synthesis conditions, nanostructured aerogels represent a promising class of materials for delivery of various drugs as well as enzymes and proteins. Along with biocompatible inorganic aerogels and biodegradable organic aerogels, more complex systems such as surface functionalized aerogels, composite aerogels and layered aerogels have also been under development and possess huge potential. Emphasis is given to the details of the aerogel synthesis and drug loading methods as well as the influence of synthesis parameters and loading methods on the adsorption and release of the drugs. Owing to their ability to increase the bioavailability of low solubility drugs, to improve both their stability and their release kinetics, there are an increasing number of research articles concerning aerogels in different drug delivery applications. This review presents an up to date overview of the advances in all kinds of aerogel based drug delivery systems which are currently under investigation.Publication Metadata only Stress/pressure-stabilized cubic polymorph of Li3Sb with improved thermoelectric performance(Royal Society of Chemistry (RSC), 2021) Soldi, Thomas; Candolfi, Christophe; Snyder, G. Jeffrey; N/A; N/A; Department of Chemistry; Yahyaoğlu, Müjde; Özen, Melis; Aydemir, Umut; PhD Student; Master Student; Faculty Member; Department of Chemistry; Koç University AKKİM Boron-Based Materials & High-technology Chemicals Research & Application Center (KABAM) / Koç Üniversitesi AKKİM Bor Tabanlı Malzemeler ve İleri Teknoloji Kimyasallar Uygulama ve Araştırma Merkezi (KABAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 58403Li3Sb has two polymorphs crystallizing in a face-centered cubic cell (c-Li3Sb; BiF3 structure type; space group Fm3m) and in a hexagonal unit cell (h-Li3Sb; Na3As structure type; space group P6(3)/mmc). c-Li3Sb was predicted to be a promising thermoelectric material based on recent first-principles studies; however, the experimental transport characteristics have remained unknown so far. Herein, successful preparation of c-Li3Sb is reported by stress-induced mechanochemical synthesis (high-energy ball milling) along with its high-temperature thermoelectric properties. Hexagonal Li3Sb (h-Li3Sb) was revealed to be the stable phase at ambient conditions, while it starts unexpectedly transforming to c-Li3Sb by ball milling or under 60 MPa applied pressure at room temperature. The transport properties measurements performed on two polycrystalline specimens evidence that c-Li3Sb behaves as a p-type degenerate semiconductor due to the formation of Li vacancies. In agreement with lattice dynamics calculations, c-Li3Sb exhibits very low lattice thermal conductivity despite the lightweight of Li. A zT value of around 0.3 was obtained at 550 K. Modelling suggests that the hole concentration should be reduced through aliovalent substitutions or under Li-rich conditions for further optimization. Although the strong air sensitivity of Li3Sb makes its use in thermoelectric applications challenging, this simple superionic binary provides an attractive experimental platform to elucidate the effect of stress/pressure on phase transitions as well as that of Fermi surface complexity on thermoelectric properties.Publication Metadata only Phase-transition-enhanced thermoelectric transport in rickardite mineral Cu3-xTe2(American Chemical Society (ACS), 2021) Prots, Yurii; El Hamouli, Oussama; Tshitoyan, Vahe; Ji, Huiwen; Burkhardt, Ulrich; Lenoir, Bertrand; Snyder, G. Jeffrey; Jain, Anubhav; Candolfi, Christophe; N/A; N/A; Department of Chemistry; Yahyaoğlu, Müjde; Özen, Melis; Aydemir, Umut; PhD Student; Master Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 58403The binary copper chalcogenides Cu2-delta X (X = S, Se, and Te) have recently gained significant interest due to their high thermoelectric performance at moderate temperatures. In an effort to unveil new Cu-based compounds with promising thermoelectric potential, Cu3-xTe2 rickardite mineral emerged as a candidate based on a purely text mining approach applied by a machine learning method. Polycrystalline samples of Cu3-xTe2 within the homogeneity range (x = 0.1, 0.2) were successfully synthesized from the raw elements by a solid-state method. High-temperature powder Xray diffraction combined with differential scanning calorimetry and specific heat measurements showed several reversible phase transitions at around 458, 640, and 647 K. Signatures of these transitions were observed on the electronic and thermal transport properties, measured over a broad range of temperatures (5-733 K). The transition undergone by this compound at 647 K results in a crossover from metallic-like to semiconducting-like properties. The combination of high power factor and low thermal conductivity in the high-temperature phase results in improved thermoelectric performances with a peak dimensionless thermoelectric figure-of-merit zT of similar to 0.14 at 733 K. The synthetic rickardite mineral is an exciting candidate to be used as a phase change material in broad application areas such as in waste heat harvesting and photovoltaic systems.Publication Metadata only Physical properties, experimental and theoretical gamma-ray shielding properties of some boron compounds(Elsevier, 2022) Ekinci, N.; El-Agawany, F., I; Gürol, A.; Rammah, Y. S.; Ahmed, Emad M.; Yılmaz, D.; Aygün, Bunyamin; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882In this study, the densities of some boron compounds as AlB12, B4C, B95, MgB2, and B86 produced in Turkey were determined experimentally. Gamma-ray shielding ability for these boron compounds was measured experimentally and compared with the estimated theoretical values via the Phy-X/PSD program. The mass attenuation coefficient was measured experimentally with Ag, Ba, Cu, Mo, Rb, and Tb radioactive sources. The obtained data for the mass attenuation coefficient via the two methods represent a good agreement. Energy dispersive x-ray fluorescence spectrometry was used in experimental procedures. All gamma-ray shielding factors such as mass and linear attenuation coefficient, half-value thickness and mean free path were calculated theoretically. The measurement results introduced the MgB2 sample as the best boron sample among all investigated boron samples.