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    PublicationOpen Access
    A novel IL/MOF/polymer mixed matrix membrane having superior CO2/N2 selectivity
    (Elsevier, 2022) Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Habib, Nitasha; Durak, Özce; Zeeshan, Muhammad; Uzun, Alper; Keskin, Seda; PhD Student; PhD Student; Faculty Member; 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); Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 59917; 40548
    In this work, we synthesized an ionic liquid (IL)/metal organic framework (MOF) composite, 1-ethyl-3-methylimidazolium acetate/copper-1,3,5-benzenetricarboxylate ([EMIM][OAc]/CuBTC) and used it as a filler in a polymer, Pebax, to fabricate novel IL/MOF/polymer mixed matrix membranes (MMMs). CuBTC/Pebax and [EMIM][OAc]/CuBTC/Pebax MMMs having different filler loadings of 10, 15, and 20 wt.% were prepared by solution casting method and characterized using various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), and thermogravimetric analysis (TGA). Uniform dispersion of MOF and IL/MOF fillers in the MMMs was observed. Incorporation of IL/MOF composite into Pebax significantly improved CO2 permeability and CO2/N2 selectivity of the polymer by 2.5- and 5.5-times, respectively. Gas permeability measurements showed that the MMM having 15 wt.% IL/MOF loading exhibits significantly higher CO2 permeability of 335 Barrer and CO2/N2 selectivity of 176 than the Pebax membrane having CO2 permeability of 135 Barrer and CO2/N2 selectivity of 32. CO2/N2 selectivity of the [EMIM][OAc]/CuBTC/Pebax MMM with 15 wt.% [EMIM][OAc]/CuBTC filler loading was the highest among the selectivity values reported for other types of IL/MOF/polymer MMMs in the literature. All the CuBTC/Pebax MMMs and [EMIM][OAc]/CuBTC/Pebax MMMs that we fabricated in this work exceeded the Robeson's updated upper bound, showing the excellent potential of these novel membranes for CO2/N2 separation.
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    Alternative fuel additives from glycerol by etherification with isobutene: structure-performance relationships in solid catalysts
    (Elsevier, 2015) Tunç, F. Meliz; Bağlar, Nur; Çelebi, Serdar; Günbaş, I. Doğan; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Bozkurt, Özge Deniz; Uzun, Alper; PhD Student; Faculty Member; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Engineering; N/A; 59917
    The expansion of biodiesel industry is expected to introduce over three million tons of glycerol into the market in 2020. Various routes have been proposed to produce glycerol-based value-added products to sustain renewable glycerol and biodiesel industries. One of these routes is the catalytic etherification of glycerol with isobutene for producing fuel oxygenate glycerol ethers as an alternative to today's petroleum based oxygenates. The products of the etherification of glycerol with isobutene are mono-, di-, and tri-tertiary butyl ethers of glycerol (MTBG, DTBG, and TTBG) and dimers of isobutene (DIE). Among these, DTBG and TTBG are the desired products for fuel blends because of their better blending properties. Different heterogeneous catalysts including acidic ion exchange resins (e.g. Amberlyst 15 and 36), sulfonated wide pore zeolites (e.g. zeolite Beta and Y), sulfonated mesoporous silica (e.g. MCM-41 and SBA-15) and some functionalized porous materials (e.g. sulfonated peanut shell, sulfonated aerogel, sulfonated graphene, spherical silica supported Hyflon) have been proved to demonstrate superior catalytic activity with complete glycerol conversion and over 90 mol% selectivity to the desired ethers. Here, we review the studies on glycerol etherification with isobutene from 1990s to the first half of 2015 specifically focusing on structure-performance relationships in heterogeneous catalysts. (C) 2015 Elsevier B.V. All rights reserved.
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    Anisotropy of ultrafine-grained alloys under impact loading: the case of biomedical niobium-zirconium
    (Pergamon-Elsevier Science Ltd, 2012) Rubitschek, F.; Niendorf, T.; Maier, H. J.; N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Toker, Sıdıka Mine; Canadinç, Demircan; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; College of Engineering; 255504; 23433
    The anisotropy-impact response relationship of a biocompatible niobium zirconium (NbZr) alloy with an ultrafine-grained microstructure was investigated. The current findings not only shed light on the micromechanisms dictating the impact response in the microstructures studied, but are also encouraging with respect to the use of NbZr in orthopedic and dental implants.
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    Atomically dispersed zeolite-supported rhodium complex: selective and stable catalyst for acetylene semi-hydrogenation
    (Academic Press Inc., 2024) Su Yordanli, Melisa; Hoffman, Adam S.; Hong, Jiyun; Perez-Aguilar, Jorge E.; Saltuk, Aylin; Akgül, Deniz; Demircan, Oktay; Ateşin, Tülay A.; Aviyente, Viktorya; Gates, Bruce C.; Bare, Simon R.; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Zhao, Yuxin; Bozkurt, Özge Deniz; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; 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); Graduate School of Sciences and Engineering; College of Engineering
    Supported rhodium catalysts are known to be unselective for semi-hydrogenation reactions. Here, by tuning the electronic structure of supported mononuclear rhodium sites determined by the metal nuclearity and the electron-donor properties of the support, we report that atomically dispersed HY zeolite-supported rhodium with reactive acetylene ligands affords a stable ethylene selectivity > 90 % for acetylene semi-hydrogenation at 373 K and atmospheric pressure, even when ethylene is present in a large excess over acetylene. Infrared and X-ray absorption spectra and measurements of rates of the catalytic reaction complemented with calculations at the level of density functional theory show how the catalyst performance depends on the electronic structure of the rhodium, influenced by the support as a ligand that is a weak electron donor.
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    Bidisperse magneto-rheological fluids consisting of functional SPIONs added to commercial MRF
    (Elsevier Science inc, 2020) N/A; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Nejatpour, Mona; Ünal, Uğur; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Faculty Member; 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; N/A; 42079; 178902
    Magnetorheological fluids (MRFs) are smart materials with a reversible and fast transition from a liquid to a semi-solid state when an external magnetic field is applied (magnetorheological effect). the sedimentation of micron-sized magnetic particles in commercial MRFs is a crucial problem limiting the long-term use in industrial applications. Here, we develop a new MRF based on commercial 140-CG LORD (R) with the addition of surface functional superparamagnetic iron oxide nanoparticles (SPIons). these new bidisperse MRFs are comprised of either poly(acrylic acid) (Paa) coated SPIons or lauric acid (La) coated SPIons and micron-sized fatty acid-coated magnetic particles of the commercial MRF. SPIons have specific coatings to interact with the fatty acid coating of the micron-sized Fe-particles. Sedimentation behaviour and the magnetorheological properties of these bidisperse MRFs with 6-12 wt % SPIon were examined. Bidisperse MRFs improved the stability and redispersibility of MRFs. Bidisperse MRFs with 12 wt% SPIon-Paa showed similar or better magnetorheological behaviour than the commercial MRF despite lower content of the micron size Fe-particles. Hence, A combination of magnetizable nano and micron-sized particles and utilization of correct surface chemistry that allows their favourable interaction improves the stability of MRFs without sacrificing magnetic response but even by improving it.
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    Bismuthene as a versatile photocatalyst operating under variable conditions for the photoredox C-H bond functionalization
    (Elsevier, 2022) Kilic, Murat; Rothlisberger, Ursula; N/A; N/A; N/A; Department of Chemistry; Department of Chemistry; Özer, Melek Sermin; Eroğlu, Zafer; Yalın, Ahsen Sare; Metin, Önder; Researcher; Researcher; PhD Student; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; N/A; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 46962
    Recently, layered two-dimensional (2D) semiconductor materials composed of group 15 elements (pnictogens) are demonstrated as efficient photocatalysts in various applications. However, only little attention is given to the investigation of their catalytic properties, and even there is no example of the photocatalytic application of bismuthene so far. Here we report for the first time on the use of 2D bismuthene as a photocatalyst in a liquidphase organic transformation. 2D bismuthene is proven to be an efficient photocatalyst that can be operated under various reaction conditions including indoor light illumination, darkness, outdoors and low temperature for the photoredox C-H arylation of (hetero)arenes with high product yields. The presented bismuthene catalyzed photoredox C-H arylation protocol works efficiently on a broad substrate scope of (hetero)arenes with aryl diazonium salts bearing electron-withdrawing and electron-donating groups. Moreover, a density functional theory (DFT) study reveals mechanistic details that lie behind the catalytic activity of bismuthene.
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    Bismuthene nanosheets as a photodynamic and photothermal antibacterial agent under NIR light illumination
    (Elsevier Inc., 2024) Cekceoglu, Ilknur Aksoy; Patir, Imren Hatay; Department of Chemistry; Department of Chemistry; Eroğlu, Zafer; Kubanaliev, Temirlan; Metin, Önder; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and Engineering
    Bacterial infections remain a significant public health burden due to the emergence of antibiotic resistance and their non-specific cytotoxic effects, leading to the search for novel antibacterial agents. Two-dimensional (2D) pnictogens, which stand out with their advantegeous properties such as large surface areas, compatibility with biological systems, and permeability across biological membranes, have emerged as potential materials in the fight against bacterial infections. By considering all these advantages, here for the first time, the antibacterial activity of 2D bismuth (Bismuthene, Biene) on Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), Gram-positive Staphylococcus aureus (S. aureus) and Methicillin-Resistant Staphylococcus aureus (MRSA) were examined under NIR light illumination. A growth curve analysis was conducted with a concentration of 256 mu g*mL-1 of exfoliated Biene nanosheets to assess the inhibition effect and corresponding antibacterial effect (%) against each bacterial strain. The photodynamic theraphy (PDT) and photothermal therapy (PTT)-mediated antibacterial mechanisms were explored by analyzing the generation of reactive oxygen species (ROS) via Glutathione (GSH) oxidation assay while a photothermal camera monitored temperature dynamic changes during irradiation. The high specific surface area-dependent membrane damage ability of Biene and morphological changes of the bacteria were visualized by field emission scanning electron microscope (FESEM). The exciting growth inhibition activity of Biene nanosheets for all bacterial strains was increased during irradiation, and breathtakingly the inhibition rate reached up to >= 99.1 % for P. aeruginosa, S. aureus, and MRSA. Besides, S. aureus and MRSA are more susceptible to Biene than E. coli and P. aeruginosa.
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    Computational assessment of MOF membranes for CH4/H2 separations
    (Elsevier, 2016) N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Eruçar, İlknur; Keskin, Seda; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; College of Engineering; 260094; 40548
    MOFs have received significant attention as gas separation membranes due to their wide range of pore sizes, permanent porosities and high surface areas. Thousands of MOFs have been reported to date. However, membrane performance of only a small number of MOFs has been experimentally reported since fabrication of thin-film MOF membranes is challenging. In this study, we used atomically-detailed simulations to assess membrane-based CH4/H-2 separation performances of 172 different MOF structures. Adsorption selectivity, diffusion selectivity, membrane selectivity and gas permeability of MOFs were calculated using atomically-detailed simulations to identify the most promising membrane materials. Our results show that a significant number of MOF membranes exhibits high CH4 selectivity over H-2 and a small number of MOF membranes exhibits mediocre H-2 selectivity over CH4. Gas permeabilities and selectivities of MOF membranes were compared with traditional membranes such as polymers and zeolites. Several MOFs were identified to exceed the upper bound established for polymeric membranes and many MOF membranes showed higher gas permeabilities and selectivities than zeolites LTA, ITQ-29 and MFI. We also carried out flexible molecular dynamics simulations to examine the effect of MOF's flexibility on the predicted membrane performance. Considering flexibility of the framework made a negligible effect on the gas permeability and selectivity of the material having large pores whereas more pronounced changes were seen in gas permeabilities of the material having narrow pores. The results of this computational study will be helpful to guide the experiments to the most promising MOF membranes for CH4/H-2 separations. (C) 2016 Elsevier B.V. All rights reserved.
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    Computational modeling of bio-MOFs for CO2/CH4 separations
    (Pergamon-Elsevier Science Ltd, 2015) N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Eruçar, İlknur; Keskin, Seda; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; College of Engineering; 260094; 40548
    Bio-metal organic frameworks (Bio-MOFs), composed of biocompatible metal cations and linker molecules such as amino acids, nucleobases and sugars, are considered as promising candidates for gas storage and separation due to their permanent porosity, chemical functionality and structural tunability. In this study, detailed molecular simulations were performed to assess the potential of 10 different bio-MOFs in adsorption-based and membrane-based separation of CO2/CH4 mixtures. After showing the good agreement between experiments and molecular simulations for single-component adsorption isotherms of several gases in various bio-MOFs, adsorption selectivity and working capacity of these materials were predicted for CO2/CH4 separation. Membrane selectivity and gas permeability of bio-MOFs were computed considering flexibility of the structures in molecular simulations for the first time in the literature. Results showed that several bio-MOFs outperform widely studied MOFs and zeolites both in adsorption-based and membrane-based CO2/CH4 separations. Bio-MOE-1, bio-MOF-11 and bio-MOF-12 were identified as promising adsorbents and membranes for natural gas purification. (C) 2015 Elsevier Ltd. All rights reserved.
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    PublicationOpen Access
    Determination of the surface electronic structure of Fe3O4(111) by soft X-ray spectroscopy
    (Elsevier, 2015) Ogasawara, Hirohito; Nilsson, Anders; Department of Chemistry; Department of Chemistry; Kaya, Sarp; Faculty Member; College of Sciences; 116541
    The determination of surface terminations in transition metal oxides is not trivial because many structural configurations could be possible. They exhibit various terminations depending on the oxidation states of metal cations exposed to the surface. Fe3O4 is one example in which octahedrally and tetrahedrally coordinated Fe2+ and Fe3+ cations coexists with oxygen anions. For the identification of the surface termination of Fe3O4(1 1 1) grown on Pt(1 1 1) we have employed surface sensitive synchrotron based X-ray photoelectron and absorption spectroscopy. It has been shown that the topmost surface is octahedrally coordinated Fe3+ rich. (C) 2014 Elsevier B.V. All rights reserved.