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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 Ae[Be2N2]: nitridoberyllates of the heavier alkaline-earth metals(Wiley-V C H Verlag Gmbh, 2004) Yaraşık, A; Akselrud, L; Leoni, S; Rosner, H; Schnelle, W; Kniep, R; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882N/APublication 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 Dynamics of architecturally engineered all-polymer nanocomposites(Amer Chemical Soc, 2018) Tyagi, Madhusudan; Pasco, Madeleine; Faraone, Antonio; Department of Chemical and Biological Engineering; Şenses, Erkan; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 280298We present nanocomposite materials formed by using glassy star-shaped polymers as nanofillers and dispersing them in soft matrices. The resulting "architecturally engineered" polymer nanocomposites structurally reside between the linear homopolymer blends and the conventional polymer nanocomposites with inorganic fillers, inducing reinforcement, which can be as strong as that of solid nanoparticles, or softening depending on the compactness and concentration of the nanoparticles. Such behavior can be traced back to the dynamical features at the local segmental and the chain level, which we investigated using neutron scattering over a wide range of time and length scales in the glassy and melt states of the nanocomposites. The local and segmental dynamics as well as the degree of chain-chain entanglements are all modified by the star-shaped fillers. The presented approach to tuning the physical properties of all-polymer-based nanocomposites is readily adaptable to other polymer architectures with immediate applications in numerous areas including gas separation membranes, tissue engineering, drug delivery, and functional coatings.Publication Metadata only Effect of Zn(NO3)(2) concentration in hydrothermal-electrochemical deposition on morphology and photoelectrochemical properties of ZnO nanorods(Elsevier, 2016) N/A; N/A; Department of Chemistry; Akkaya, Ceren Yılmaz; Ünal, Uğur; PhD Student; Faculty Member; Department of Chemistry; N/A; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 42079Zn(NO3)(2) concentration had been reported to be significantly influential on electrodeposition of ZnO structures. In this work, this issue is revisited using hydrothermal-electrochemical deposition (HED). Seedless, cathodic electrochemical deposition of ZnO films is carried out on ITO electrode at 130 degrees C in a closed glass reactor with varying Zn(NO3)(2) concentration. Regardless of the concentration of Zn2+ precursor (0.001-0.1 M) in the deposition solution, vertically aligned 1-D ZnO nanorods are obtained as opposed to electrodepositions at lower temperatures (70-80 degrees C). We also report the effects of high bath temperature and pressure on the photoelectrochemical properties of the ZnO films. Manipulation of precursor concentration in the deposition solution allows adjustment of the aspect ratio of the nanorods and the degree of texturation along the c-axis; hence photoinduced current density. HED is shown to provide a single step synthesis route to prepare ZnO rods with desired aspect ratio specific for the desired application just by controlling the precursor concentration.Publication Metadata only Efficient synthesis of bifeo3 by the microwave-assisted sol-gel method: "a" site influence on the photoelectrochemical activity of perovskites(Elsevier, 2019) Singh, Dheerendra; Tabari, Taymaz; Ebadi, Mehdi; Trochowski, Mateusz; Macyk, Wojciech; N/A; Yağcı, Mustafa Barış; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/ABiFeO3 (BF) and LaFeO3 (LF) perovskites were synthesized using a microwave-assisted (MW) and sol-gel (SG) methods. XRD, XPS, TEM, UV-DRS techniques were applied to study physicochemical properties of perovskites. In addition, Incident Photon-to-Current Efficiency (IPCE) measurements, Linear Sweep Voltammetry (LSV) and impedance spectroscopy were used to characterize electrochemical properties of the materials. The band gap energy increases in the following way: BF-MW (2.05 eV), LF-MW (2.18 eV), BF-SG (2.26 eV) and LF-SG (2.54 eV), demonstrating a remarkable influence of the synthesis method on the optical and electronic properties of the materials. Furthermore, XRD showed a significant impact of the synthesis methods on the crystal structure. Perovskites synthesized under MW irradiation showed a pure crystal structure compared to the perovskites prepared by SG method, which contained some admixtures. IPCE shows that LF-MW has a better charge separation ability compared to BF-MW. However, BF-SG showed the highest activity. Temperature programmed reduction tests (TPR) revealed a better ability of BF-MW to adsorb/desorb oxygen, compared to LF-MW. XPS measurements pointed at the presence of Fe4+. Finally, the photocatalytic activity of the perovskites was tested in solar water-splitting as a function of the synthesis method and presence of Bi and La in "A" sites of the ABO(3) perovskites. We postulate, that the Jahn-Teller distortion effect in LF-MW increases its catalytic activity by decreasing the binding energy compared to BF-MW.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 Influence of hydrogen bond on the mesomorphic behaviour in urethane based liquid crystalline compounds: experimental and computer simulation study(Elsevier, 2020) Korkmaz, Burak; Agtas, Sinem; Sutay, Berkay; Yıldırım, Erol; Yurtsever, Mine; Senkal, B. Filiz; Gürsel, Yeşim; Department of Chemistry; Yılgör, İskender; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; 24181We present a combined experimental and theoretical study on the novel hydrogen-bonded liquid crystalline complex (UR-LC11) exhibiting both nematic and smectic phases upon cooling. The complex was prepared by mixing 2-(2-methoxyethoxy)ethylbutyl carbamate (UR) as H-bond acceptor with calamitic mesogen 4 '-((11-hydroxyundecyl)oxy)-[1,1 '-biphenyl]-4-carbonitrile (LC11) as H-bond donor. The complex was characterized by FTIR technique and its liquid crystalline properties were studied by differential scanning calorimetry (DSC) and polarized optical microscope (POM). The experimental IR spectra were compared with theoretically obtained IR spectra by Density Functional Theory (DFT) to suggest the structure of hydrogen-bonded liquid crystal (LC). The molecular dynamics (MD) simulationswere performed to understand the impact of hydrogen bonding on the mesomorphic behaviour of the complex and the temperature dependency of the transitions between the mesophases. We determined that UR-LC11 is a stable H-bond acceptor/donor type complex and a single H-bond forms between the carbonyl oxygen atom of the amidemoiety of UR and the hydrogen atomof the terminal hydroxyl group of the LC11. Although LC11 is present only in nematic liquid crystalline form, the new complex displayed both nematic and smectic phases during cooling. The reason for the two distinctive LC phases was explained by the presence of hydrogen bond interactions, which provides structural flexibility. Besides, H-bond maintains uniaxial rod shape of the molecule to promote self-assembly behaviour and induces positional ordering in the smectic phase. The enhancement in the self-assembly of the H-bonded chains in the complex is reflected in the increased.Hfusion values. Due to the intermolecular p-p interactions of the phenyl rings and the formation of strong dipoles on the backbone, especially at the cyanobiphenyl end of the chains, the longrange directional order of the dipoles along their long axes are preserved at elevated temperatures and nematic to isotropic phase transition is observed at around 370 K both experimentally and theoretically.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 Investigation of the hydrogen gas sensing properties of nanoporous Pd alloy films based on AAO templates(Elsevier, 2011) Öztürk, Sadullah; Kılınç, Necmettin; Öztürk, Zafer Ziya; Department of Physics; Taşaltın, Nevin; Researcher; Department of Physics; College of Sciences; 220956In this study, the hydrogen sensing properties of nanoporous Pd-Ag and Pd-Cu alloy films based on anodic aluminum oxide (AAO) templates were investigated at various temperatures (25-100 degrees C) and hydrogen with concentrations in the range between 250 and 5000ppm in high purity nitrogen to determine the temperature-sensitivity relationship. A hexagonally shaped AAO template of approximately 50nm in diameter and 10 mu m in length was fabricated as a substrate for supporting a nanoporous Pd alloy film with an approximate thickness of 80 nm. The morphologies of the AAO template and the Pd alloy films were studied by scanning electron microscopy (SEM). The hydrogen sensing properties of the nanoporous Pd-Ag and Pd-Cu alloy films were measured using a transient resistance method. The sensor responses of the nanoporous Pd-Ag and Pd-Cu films on the AAO template were better than the traditional Pd-Ag and Pd-Cu thin film sensors; the sensitivities of the sensors were approximately 1.6% and 1.2%, respectively, for 1000ppm H(2), and the detection limit was 250ppm at room temperature. The highest sensitivity was measured at room temperature for all alloy nanoporous sensors, and the sensitivity of the Pd-Ag nanoporous alloy was higher than that of the Pd-Cu nanoporous alloy.