Publications without Fulltext
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
Browse
93 results
Filters
Advanced Search
Filter by
Settings
Search Results
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 Motion of single terrylene molecules in confined channels of poly(butadiene)-poly(ethylene oxide) diblock copolymer(Amer Chemical Soc, 2009) N/A; Department of Physics; Department of Chemistry; Yorulmaz, Mustafa; Kiraz, Alper; Demirel, Adem Levent; Master Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 22542; 6568The motion of terrylene probe molecules in confined PB channels of an asymmetric PB-PEO diblock copolymer has been investigated by single molecule tracking. The one-dimensional diffusion coefficients were found to be significantly smaller and had a narrower distribution compared to two-dimensional diffusion coefficients in PB. The trajectories of some single molecules showed unusual behavior of directed motion where mean square displacement had a parabolic dependence oil lag time. The likely origin of this behavior is discussed in terms of local variations in the PB channel width and the resulting change in the local density. The results show the effect of nonuniformities and heterogeneities in the channels on the motion of single molecules and demonstrate the sensitivity of single molecule tracking in characterizing self-assembled block copolymer morphologies.Publication Metadata only Synthesis of upconverting nanosheets derived from Er-Yb and Tm-Yb Co-doped layered perovskites and their layer-by-layer assembled films(Elsevier, 2022) Gunay, Bensu; Suer, Ozge; Doger, Hilal; Arslan, Ozlem; Saglam, Ozge; Department of Chemistry; Ünal, Uğur; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; 42079Here, we investigated the structure and upconversion (UC) properties of new-type of single oxide nanosheets, derived from the Er3+/Yb3+ and Tm3+/Yb3+ co-doped Ruddlesden-Popper type layered perovskites, and their layer-by-layer (LBL) self-assembled nanofilms. The single oxide nanosheets, obtained by exfoliation of the proton-exchanged K2La2Ti3O10, had the thickness in the range of 2-3 nm indicating good consistency with the theoretical thickness and lateral size from 500 nm up to 2 mu m. Er3+/Yb3+, Tm3+/Yb3+ and Tm3+/Er3+co-doped nanosheets were used as building blocks of the multilayer films deposited by layer-by-layer procedure. The LBL films composed of 2.5 % Er3+ + 5 % Yb3+, 2.5 % Tm3+ + 20 % Yb3+, 2.5 % Tm3+ + 20 % Er3+ after 60 sequences have shown a white emission confirmed by the CIE chromaticity diagram. The possible UC energy transfer of LBL films fabricated after 30 sequences using the nanosheets derived from the 2.5 % Er3+ + 5 % Yb3+ co-doped layered perovskites was also suggested. The number of photons participating in the UC process was confirmed as two-photon for both green and red UC emissions due to the F-4(9/2) -> I-4(15/2) and H-2(11/2), S-4(3/2) -> I-4(15/2) transitions, respectively.Publication Metadata only The first alkaline-earth azidoaurate(III), Ba[Au(N-3)(4)](2) center dot 4 H2O(Wiley, 2023) Prots, Yurii; Jach, Franziska; Afyon, Semih; Höhn, Peter; Department of Chemistry; Department of Chemistry; Department of Chemistry; Subaşı, Yaprak; Tekin, Elif Sena; Somer, Mehmet Suat; Researcher; Undergraduate Student; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 178882Transparent, dark orange Ba[Au(N-3)(4)](2) center dot 4 H2O was synthesized by reaction of Ba(N-3)(2) and AuCl3 or HAuCl4 in aqueous solution. The novel barium tetraazidoaurate(III) tetrahydrate crystallizes in the monoclinic space group Cc (no. 9) with a=1813.68(17) pm, b=1737.95(11) pm, c=682.04(8) pm and beta=108.849(4)degrees. The predominant structural features of Ba[Au(N-3)(4)](2) center dot 4 H2O are two crystallographically independent discrete anions [Au(N-3)(4)](-) with gold in a tetragonal planar coordination by nitrogen. Vibrational spectra show good agreement with those of other azidoaurates(III). Upon drying, this salt was shown to be a highly explosive material.Publication Metadata only Nanoparticle silicalite-1 crystallization from clear solutions: nucleation(Elsevier Science Bv, 2009) Tokay, Begüm; Erdem-Şenatalar, Ayşe; Schueth, Ferdi; Thompson, Robert W.; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882Despite much effort spent by various research groups, there remain many aspects of nanoparticle silicalite-1 crystallization from clear solutions which require further investigation. In order to shed light, especially on the nucleation of silicalite-1, particle growth at 100 degrees C from several starting compositions known to yield colloidal silicalite-1, which have been studied previously by other researchers using various techniques, was followed in this study by laser light scattering using scattering angles of 90 degrees and 173 degrees, and zeta potential and pH measurements. Crystallinity was monitored by X-ray diffraction, Fourier transform infrared analysis and transmission electron microscopy. Thermogravimetric analyses and density measurements were also used to characterize the products obtained at various times during the syntheses. The results demonstrate that the distinct time of sudden jump in the effective diameter of the nanoparticles in solution, as observed more clearly by using the back-scattering device, and which marks the beginning of the constant linear growth rate of the particles, corresponds to the nucleation of the silicalite-1 crystal structure. This time was also shown to coincide with the exo-endo thermal switch time of the reaction mechanism, which has been observed previously by another research group. Nucleation was accompanied by an aggregation of a population of smaller particles, as indicated by the broadening of the particle size distribution, and the variation of the pH and zeta potential values during synthesis.Publication Metadata only Pi-stack dimers of small polyaromatic hydrocarbons: a path to the packing of graphenes(Amer Chemical Soc, 2009) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129MP2 calculations of the stacking energy are reported for the dimers of a set of polycyclic aromatic hydrocarbons. The interaction strengths and their dependence on the shape-dependent measures as well as the aromatic character of the monomer are studied. For small systems involving four to six rings, the noncovalent interactions seem to be independent of the shape of the monomers. The most preferred conformations for parallel stacked dimers are not aligned exactly but off-center with small shifts; however, these shifts are on the order of 1 angstrom, and the energy necessary to keep them aligned is less than 0.5 kcal/mol per ring. Small-angle rotations within the molecular planes also do not require much energy, and in some cases they lead to stronger interactions.Publication Metadata only High voltage LiCoO2 cathodes with high purity lithium Bis(oxalate) Borate (LiBOB) for lithium-ion batteries(American Chemical Society (ACS), 2022) Afyon, Semih; Department of Chemistry; Subaşı, Yaprak; Researcher; Department of Chemistry; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; N/ALithium bis(oxalate) borate, LiB(C2O4)(2) (LiBOB) can be used as an electrolyte additive for lithium-ion batteries (LIBs) to prevent structural change and electrolyte decomposition by developing a protective solid electrolyte interphase (SEI) on the cathode surface. However, impurities present in LiBOB result in significant electrochemical performance decays related to higher full cell impedance. Here, a practical purification technique is performed to remove these impurities within the as-synthesized anhydrous LiBOB in which we further add 1 wt % in 1 M LiPF6 in EC:DMC (1:1) electrolytes to achieve a more stable cycling performance for high voltage applications of LiCoO2 (LCO) cathodes. The phase and purity of as-synthesized LiBOB and recrystallized LiBOB is determined by a combination of X-ray powder diffraction (XRPD), Fourier-transform infrared (FTIR) spectra, and scanning electron microscopy (SEM) measurements. The LIB performance with the addition of high purity LiBOB as an electrolyte additive is investigated via galvanostatic charge-discharge cycling, rate capability, and cyclic voltammetry (CV) measurements within a voltage range of 3.0-4.4 V. The cell containing 1 wt % recrystallized LiBOB shows superior cycling performance, rate capability with higher energy density, and Coulombic efficiency in comparison with the reference cell through the formation of a passivation layer on the LCO surface. Thus, for the LiBOB added cell, the crystal structure of LiCoO2 is well-maintained even at higher potentials after 100 cycles according to the ex situ XRPD and SEM analyses. Therefore, high-purity LiBOB improves the interfacial stability of the LCO cathode by inhibiting oxidative decomposition of electrolytes, undesirable structural changes, and cobalt dissolution bringing about safer cycling even at high operation voltages.Publication Metadata only Platelets to rings: influence of sodium dodecyl sulfate on zn-al layered double hydroxide morphology(Academic Press Inc Elsevier Science, 2012) N/A; Department of Chemistry; Department of Chemistry; Akkaya, Ceren Yılmaz; Ünal, Uğur; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 42079; 178902; 179997In the current study, influence of sodium dodecyl sulfate (SDS) on the crystallization of Zn-Al layered double hydroxide (LDH) was investigated. Depending on the SDS concentration coral-like and for the first time ring-like morphologies were obtained in a urea-hydrolysis method. It was revealed that the surfactant level in the starting solution plays an important role in the morphology. Concentration of surfactant equal to or above the anion exchange capacity of the LDH is influential in creating different morphologies. Another important parameter was the critical micelle concentration (CMC) of the surfactant. Surfactant concentrations well above CMC value resulted in ring-like structures. The crystallization mechanism was discussed.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 Polyurethane synthesis revisited: effect of solvent and reaction conditions on prepolymer formation and polymer properties(American Chemical Society (ACS), 2014) N/A; Department of Chemistry; Department of Chemistry; Yıldırım, Armen; Yılgör, Emel; Yılgör, İskender; Master Student; Researcher; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; College of Sciences; College of Sciences; N/A; 40527; 24181N/A