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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 A post-HF study on the halogen bonding interaction of pyrene with diatomic halogen molecules(Wiley, 2016) Sütay, Berkay; Yurtsever, Mine; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129We present a detailed SCS-MP2 study on the potential energy curves (PEC) for interactions between diatomic halogen molecules and pyrene. BSSE corrected CCSD[T] energies at equilibrium distances are computed and compared to CCSD(T) energies. The most stable conformation of these weakly bound van der Waals complexes is almost linear in the perpendicular direction to the pyrene plane. The complexes of highly polarizable bromine and iodine molecules with pyrene are very stable and they carry rather large number of vibrational states. Despite its small size, F-2 also forms strong halogen bonding similar to Br-2 and I-2. The interaction between Cl-2 and pyrene is the weakest and it is attributed to the highest polarizability/molar mass ratio of chlorine among the others. I-2-pyrene is found to be the most stable complex due to the strongest mutual polarization effects and is carrying more than 60 vibrational states. Due to the rather large number of electrons in some complexes, the relativistic corrections are also considered.Publication Metadata only Advancing the understanding of the structure-activity-durability relation of 2D MoS2 for the hydrogen evolution reaction(Amer Chemical Soc) N/A; N/A; Department of Chemistry; Solati, Navid; Karakaya, Cüneyt; Kaya, Sarp; PhD Student; PhD Student; 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; College of Sciences; N/A; N/A; 116541It has been decades since electrochemical water splitting was proposed as a promising strategy for renewable hydrogen production. Transition-metal dichalcogenides offer cheap, earth-abundant catalyst candidates for the hydrogen evolution reaction (HER). Among those, molybdenum disulfide (MoS2) has been the subject of a vast number of studies, where different approaches such as manipulating the type and number of layers, or density of the intrinsic active sites, and engineering compositional phase and structure have been employed to enhance the electrochemical activity. Herein, we show the HER activities of twodimensional 1T-and 1H-MoS2 mixed phases with respect to the pure 1H-MoS2 scale with the 1T phase. The creation of S vacancies in 1H-MoS2 enhances HER activities. Further enhancement in the activity is achieved by N doping induced by N2 plasma exposure owing to the formation of a metallic 1T phase and S vacancies. The spectroelectrochemical Raman spectroscopy and ex-situ X-ray photoelectron spectroscopy investigations reveal a gradual phase conversion induced by H adsorption during electrochemical tests. The 1T to 1H phase transformation results in a significant loss in HER activity.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 AFM investigation of segmented, highly branched polyurethaneureas(American Chemical Society (ACS), 2006) Fornof, Ann R.; Long, Timothy E.; Sheth, Jignesh; Wilkes, Garth L.; Department of Chemistry; Department of Chemistry; Department of Chemistry; Yılgör, İskender; Yılgör, Emel; Ünal, Serkan; Faculty Member; Researcher; Undergraduate Student; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; 24181; 40527; 241611N/APublication Metadata only Alpha- and beta-na-2[BH4][NH2]: two modifications of a complex hydride in the system NaNH2-NaBH4; syntheses, crystal structures, thermal analyses, mass and vibrational spectra(Elsevier Science Sa, 2010) Höhn, Peter; Cardoso-Gil, Raul; Aydemir, Umut; Akselrud, Lev; Department of Chemistry; N/A; N/A; N/A; Somer, Mehmet Suat; Acar, Selçuk; Koz, Cevriye; Kokal, İlkin; Faculty Member; PhD Student; Master Student; Master Student; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 178882; N/A; N/A; N/AThe title compound Na-2[BH4][NH2] Na2BNH6 exists in two different modifications: the low-temperature (LT) beta- and the high-temperature (HT) alpha-phase. The HT alpha-Na2BNH6 is accessible by single heating of the binaries NaNH2 and NaBH4 (molar ratio = 1:1) to the melting point of 492 K for I h in evacuated Pyrex ampoules. on longer annealing (T = 342 K, 10 days), the HT alpha-phase converts completely to the LT beta-phase. The beta -> alpha transition at 371 K is very fast, but the conversion alpha -> beta is quite slow. No further phase formation was detected in the system up to a molar ratio of 5:1 (NaNH2:NaBH4). The cubic alpha-Na2BNH6 crystallizes in the K3SO4F-type of structure (space group: Pm (3) over barm, Z = 1) with a = 4.6950(1) angstrom. beta-Na2BNH6 crystallizes in orthorhombic symmetry (space group: Pbcm, Z = 4) with a = 6.5384(2) angstrom. b = 6.4960(1) angstrom, c=9.8512(2)angstrom. Both structures can directly be derived from the perovskite type structure ABO(3), with the [BH4](-) and [NH2](-) moieties in the A and B sites, respectively. The charge balancing Na ions are occupying 2/3 of the O positions. In both cases, the presence of the two different anions in the solids was also confirmed by vibrational spectra. According to DTA and high temperature X-ray diffraction (HT-XRD) measurements, the educts NaNH2 and NaBH4 react at 430 K to form alpha-Na2BNH6 which remains stable until the melting point of 492 K. Between 492 and 573 K, no significant effects were detected in DTA and TG. Above 573 K, however, a sudden decomposition takes place in two steps (659 and 689 K) causing a total mass loss of 8%. The gaseous species formed during the decomposition process were followed by mass spectra (MS). The mass spectra obtained from 1:1 and 2:1 mixtures of NaNH2 and NaBH4 in the range 492 K < T < 773 K prove that the main gaseous product evolved during the thermal decomposition is H-2. NH3 and H2O were also detected, but their concentrations are quite low. These findings confirm that the mixture of the complex hydrides NaNH2-NaBH4 (molar ratio >= 1:1) - comparable to the LiNH2-LiBH4 system - are potential candidates for solid hydrogen storage materials. The composition of the solid residues after the thermal treatment depends on the molar ratio of the starting binaries NaNH2 and NaBH4. While Na2BNH6 (1:1) decomposes to a mixture of NaH, Na and an unidentified amorphous solid, mixtures >= 2:1 yielded exclusively Na3BN2. The vibrational spectra of the title compounds Na2BNH6 have been measured and interpreted based on the T-d and C-2v symmetry of the relevant [BH4](-) and [NH2](-) groups. Both the (N-H) and (B-H) frequencies exhibit small but significant shifts with respect to the pure binaries.Publication Metadata only An advantageous technique to load drugs into aerogels: gas antisolvent crystallization inside the pores(Elsevier Science Bv, 2017) 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 years, both organic and inorganic nanoporous aerogels have shown a great promise as drug delivery vehicles. Different methods are utilized to load drugs into aerogels such as the addition of the drug to the reaction mixture in one of the steps before the gel formation or by supercritical deposition to the aerogels. These techniques have disadvantages such as possible reactions of pharmaceutical compounds with reactants used to form gels and low solubility of pharmaceutical compounds in supercritical carbon dioxide (scCO(2)). An alternative technique is to load the drug after gel formation by contacting the gel with a solution of the drug. The drug diffuses into the liquid inside the pores. When this drug-loaded gel is subjected to supercritical drying, scCO(2) not only removes the solvent from the pores but also acts as an antisolvent, which causes the precipitation of the drug in the pores of the aerogel. This is similar to the gas antisolvent crystallization (GAS) process but in this case the process takes place inside the pores. In this study, this technique was used to load paracetamol into silica aerogels. The factors affecting the amount and distribution of the drug inside the aerogel matrix were investigated and a mathematical model to account for the movement of paracetamol inside the pores during supercritical drying leading to a varying drug concentration in the matrix with position was developed. It was concluded that high initial concentrations resulted in more homogeneous drug distributions. Moreover, XRD analysis demonstrated that paracetamol was in crystalline form. The process enables higher amount of loadings than conventional systems and also offers an advantage as it combines two processes such as drying and loading in a single one reducing the time and the operating expenses.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 Antibacterial silicone-urea/organoclay nanocomposites(Springer, 2009) Department of Chemistry; N/A; N/A; Department of Chemistry; Yılgör, Emel; Nugay, Işık Işıl; Bakan, Murat; Yılgör, İskender; Researcher; Undergraduate Student; Undergraduate Student; Faculty Member; Department of Chemistry; College of Sciences; College of Engineering; College of Engineering; College of Sciences; N/A; N/A; N/A; 24181Montmorillonite modified with distearyldimethyl ammonium chloride (C18-QAC) (Nanofil-15) (NF15) was incorporated into polydimethylsiloxane-urea (silicone-urea, PSU) copolymers. PSU was obtained by the reaction of equimolar amounts of aminopropyl terminated polydimethylsiloxane (PDMS) oligomer (= 3,200 g/mol) and bis(4-isocyanatohexyl) methane (HMDI). A series of PSU/NF15 nanocomposites were prepared by solution blending with organoclay loadings ranging from 0.80 to 9.60% by weight, corresponding to 0.30 to 3.60% C18-QAC. Colloidal dispersions of organophilic clay (NF15) in isopropanol were mixed with the PSU solution in isopropanol and were subjected to ultrasonic treatment. Composite films were obtained by solution casting. FTIR spectroscopy confirmed that the organoclay mainly interacted with the urea groups but not with PDMS. XRD analysis showed that nanocomposites containing up to 6.40% by weight of organoclay had fully exfoliated silicate layers in the polymer matrix, whereas 9.60% loading had an intercalated structure. Physicochemical properties of nanocomposites were determined. PSU/NF15 nanocomposites displayed excellent long-term antibacterial properties against E. coli.Publication Metadata only Assessment of acid strength in sodium-exchanged resin catalysts: consequences on glycerol etherification with isobutene in batch and flow reactors(Elsevier Science Bv, 2019) Department of Chemical and Biological Engineering; N/A; Uzun, Alper; Bozkurt, Özge Deniz; Faculty Member; PhD Student; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; Graduate School of Sciences and Engineering; 59917; N/AConsequences of a decrease in the number of acid sites by the cation exchange on the acid strength of the resin catalysts were assessed using ammonia as a probe molecule. IR spectra illustrated that v(N-H) bands on NH3-saturated Amberlyst 15 (TM) shift linearly to higher frequencies with an increase in the degree of sodium exchange associated with an increase in the Bronsted acid strength. These results were further confirmed by density functional theory calculations illustrating that the deprotonation energy of a sulfonated styrene group decreases upon Na+-exchange on its neighboring counterparts. Consequences of these changes in acid strength were investigated on glycerol etherification with isobutene. Batch reactor measurements at high conversions illustrated that selectivity to desired glycerol ethers increases as that of isobutene dimerization is suppressed with an increase in acid strength. The effects of acid strength on the complex reaction network were further investigated using a once-through flow reactor specifically focusing on low conversions. These measurements showed that mono-tert-butyl glycerol ether and di-isobutene were the primary products on pristine Amberlyst 15 (TM), while di-and tri-tert-butyl glycerol ethers also become a primary product on sodium-exchanged counterpart catalysts.