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Altıntaş, Çiğdem

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Çiğdem

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Altıntaş

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Altıntaş, Çiğdem

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2015 - 2019122020 - 202316

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    Metal-organic framework-based materials for the abatement of air pollution and decontamination of wastewater
    (PERGAMON-ELSEVIER SCIENCE LTD, 2022) Erucar, Ilknur; Heidari, Golnaz; Zare, Ehsan Nazarzadeh; Moradi, Omid; Srivastava, Varsha; Iftekhar, Sidra; Sillanpaa, Mika; N/A; N/A; Department of Chemical and Biological Engineering; Harman, Hilal Dağlar; Altıntaş, Çiğdem; Keskin, Seda; PhD Student; Researcher; Faculty Member; Department of Chemical and Biological Engineering; N/A; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 40548
    Developing new and efficient technologies for environmental remediation is becoming significant due to the increase in global concerns such as climate change, severe epidemics, and energy crises. Air pollution, primarily due to increased levels of H2S, SOx, NH3, NOx, CO, volatile organic compounds (VOC), and particulate matter (PM) in the atmosphere, has a significant impact on public health, and exhaust gases harm the natural sulfur, nitrogen, and carbon cycles. Similarly, wastewater discharged to the environment with metal ions, herbicides, pharmaceuticals, personal care products, dyes, and aromatics/organic compounds is a risk for health since it may lead to an outbreak of waterborne pathogens and increase the exposure to endocrine-disrupting agents. Therefore, developing new and efficient air and water quality management systems is critical. Metal-organic frameworks (MOFs) are novel materials for which the main application areas include gas storage and separation, water harvesting from the atmosphere, chemical sensing, power storage, drug delivery, and food preservation. Due to their versatile structural motifs that can be modified during synthesis, MOFs also have a great promise for green applications including air and water pollution remediation. The motivation to use MOFs for environmental applications prompted the modification of their structures via the addition of metal and functional groups, as well as the creation of heterostructures by mixing MOFs with other nanomaterials, to effectively remove haz-ardous contaminants from wastewater and the atmosphere. In this review, we focus on the state-of-the-art environmental applications of MOFs, particularly for water treatment and air pollution, by highlighting the groundbreaking studies in which MOFs have been used as adsorbents, membranes, and photocatalysts for the abatement of air and water pollution. We finally address the opportunities and challenges for the environmental applications of MOFs.
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    Computational investigation of dual filler-incorporated polymer membranes for efficient CO2 and H2 separation: MOF/COF/Polymer mixed matrix membranes
    (American Chemical Society (ACS), 2023) Erucar, Ilknur; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Aydın, Sena; Altıntaş, Çiğdem; Keskin, Seda; Master Student; Researcher; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 40548
    Mixed matrix membranes (MMMs) composed of two different fillers such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) embedded into polymers provide enhanced gas separation performance. Since it is not possible to experimentally consider all possible combinations of MOFs, COFs, and polymers, developing computational methods is urgent to identify the best performing MOF-COF pairs to be used as dual fillers in polymer membranes for target gas separations. With this motivation, we combined molecular simulations of gas adsorption and diffusion in MOFs and COFs with theoretical permeation models to calculate H2, N2, CH4, and CO2 permeabilities of almost a million types of MOF/COF/polymer MMMs. We focused on COF/polymer MMMs located below the upper bound due to their low gas selectivity for five industrially important gas separations, CO2/N2, CO2/ CH4, H2/N2, H2/CH4, and H2/CO2. We further investigated whether these MMMs could exceed the upper bound when a second type of filler, a MOF, was introduced into the polymer. Many MOF/COF/polymer MMMs were found to exceed the upper bounds showing the promise of using two different fillers in polymers. Results showed that for polymers having a relatively high gas permeability (>= 104 barrer) but low selectivity (<= 2.5) such as PTMSP, addition of the MOF as the second filler can have a dramatic effect on the final gas permeability and selectivity of the MMM. Property-performance relations were analyzed to understand how the structural and chemical properties of the fillers affect the permeability of the resulting MMMs, and MOFs having Zn, Cu, and Cd metals were found to lead to the highest increase in gas permeability of MMMs. This work highlights the significant potential of using COF and MOF fillers in MMMs to achieve better gas separation performances than MMMs with one type of filler, especially for H2 purification and CO2 capture applications.
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    A ruthenium racemisation catalyst for the synthesis of primary amines from secondary amines
    (Royal Soc Chemistry, 2016) Pingen, Dennis; Schaller, Max Rudolf; Vogt, Dieter; N/A; Altıntaş, Çiğdem; Researcher; N/A; N/A
    A Ru-based half sandwich complex used in amine and alcohol racemization reactions was found to be active in the splitting of secondary amines to primary amines using NH3. Conversions up to 80% along with very high selectivities were achieved. However, after about 80% conversion the catalyst lost activity. Similar to Shvo's catalyst, the complex might deactivate under the influence of ammonia. It was revealed that not NH3 but mainly the primary amine is responsible for the deactivation.
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    Enhanced water stability and high CO2 storage capacity of a Lewis basic sites-containing zirconium metal-organic framework
    (2021) Demir, Selçuk; Bilgin, Nuray; Çepni, Hamide Merve; Furukawa, Hiroyasu; Yılmaz, Fatih; N/A; Department of Chemical and Biological Engineering; Altıntaş, Çiğdem; Keskin, Seda; Researcher; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 40548
    Metal–organic frameworks (MOFs) are an emerging class of materials employed for custom-designed purposes by judicious selection of linkers and metal ions. Among the MOFs composed of carboxylate linkers, Zr-based MOFs have attracted great attention due to their high thermal and chemical stabilities, which are important for practical applications, including capturing CO2 from a point source. UiO-67(bipy) containing 2,2′-bipyridine-5,5′-dicarboxylate is particularly useful among the Zr-MOF family due to the Lewis basic sites of the linker; however, the hydrolytic stability of UiO-67(bipy) does not seem to be as high as those of UiO-66 and UiO-67. To improve the hydrolytic stability without sacrificing the adsorption enthalpy of CO2 for selective CO2 capture, in this study, we added hydrophobic methyl groups to the backbone of the bipyridine linker. The synthesized 6,6′-dimethyl-2,2′-bipyridine-5,5′-dicarboxylic acid (H2Me2bipy) was used to prepare a Zr-based MOF [MOF-553, Zr6O4(OH)4(Me2Bipy)6]. In addition, the water stability and CO2 adsorption capacity of MOF-553 were compared to those of UiO-67(bipy). We revealed that MOF-553 is more robust and has a higher CO2 adsorption capacity than UiO-67(bipy), indicating that the methylation of the linker improves the water stability of the framework, which is advantageous for point-source CO2 capture.
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    Oxalamide-functionalized metal organic frameworks for CO2 adsorption
    (American Chemical Society (ACS), 2021) Guclu, Yunus; Erer, Hakan; Demiral, Hakan; Tumanov, Nikolay; Su, Bao-Lian; Semerci, Fatih; Department of Chemical and Biological Engineering; N/A; Keskin, Seda; Altıntaş, Çiğdem; Faculty Member; Researcher; Department of Chemical and Biological Engineering; College of Engineering; Graduate School of Sciences and Engineering; 40548; N/A
    Metal–organic frameworks (MOFs) have received great attention in recent years as potential adsorbents for CO2 capture due to their unique properties. However, the high cost and their tedious synthesis procedures impede their industrial application. A series of new CO2-philic oxalamide-functionalized MOFs have been solvothermally synthesized: {[Zn3(μ8-OATA)1.5(H2O)2(DMF)]·5/2H2O·5DMF}n (Zn-OATA), {[NH2(CH3)2][Cd(μ4-HOATA)]·H2O·DMF}n (Cd-OATA), and {[Co2(μ7-OATA)(H2O)(DMF)2]·2H2O·3DMF}n (Co-OATA) (H4OATA = N,N′-bis(3,5-dicarboxyphenyl)oxalamide). In Zn-OATA, the [Zn2(CO2)4] SBUs are connected by OATA4– ligands into a 3D framework with 4-connected NbO topology. In Cd-OATA, two anionic frameworks with a dia topology interpenetrated each other to form a porous structure. In Co-OATA, [Co2(CO2)4] units are linked by four OATA4– to form a 3D framework with binodal 4,4-connected 42·84 PtS-type topology. Very interestingly, Cu-OATA can be prepared from Zn-OATA by a facile metal ions exchange procedure without damaging the structure while the CO2 adsorption ability can be largely enhanced when Zn(II) metal ions are exchanged to Cu(II). These new MOFs possess channels decorated by the CO2-philic oxalamide groups and accessible open metal sites, suitable for highly selective CO2 adsorption. Cu-OATA exhibits a significant CO2 adsorption capacity of 25.35 wt % (138.85 cm3/g) at 273 K and 9.84 wt % (50.08 cm3/g) at 298 K under 1 bar with isosteric heat of adsorption (Qst) of about 25 kJ/mol. Cu-OATA presents a very high selectivity of 5.5 for CO2/CH4 and 43.8 for CO2/N2 separation at 0.1 bar, 298 K. Cd-OATA exhibits a CO2 sorption isotherm with hysteresis that can be originated from structural rearrangements. Cd-OATA adsorbs CO2 up to 11.90 wt % (60.58 cm3/g) at 273 K and 2.26 wt % (11.40 cm3/g) at 298 K under 1 bar. Moreover, these new MOFs exhibit high stability in various organic solvents, water, and acidic or basic media. The present work opens a new opportunity in the development of improved and cost-effective MOF adsorbents for highly efficient CO2 capture.
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    Two-dimensional oxalamide based isostructural MOFs for CO2 capture
    (Academic Press Inc Elsevier Science, 2023) Guclu, Yunus; Erer, Hakan; Demiral, Hakan; Zorlu, Yunus; Semerci, Fatih; Department of Chemical and Biological Engineering; Keskin, Seda; Altıntaş, Çiğdem; Faculty Member; Researcher; Department of Chemical and Biological Engineering; College of Engineering; 40548; N/A
    Metal-organic frameworks (MOFs), members of porous crystalline materials, have been investigated for CO2 capture and separation from various exhaust gas mixtures. An essential element to build new MOFs with improved CO2 capture and separation abilities is to understand the influence of functional groups on the surface of pores on gas adsorption properties. Oxalamide groups have two amide moieties that feature a strong affinity to CO2. In this study, three new isostructural Co(II), Zn(II), and Cd(II)-MOFs have been synthesized by using 3,3'-(oxalylbis(a-zanediyl))dibenzoic acid (3-OADAH2) ligand which has a CO2-philic oxalamide group. To the best of our knowledge 3,3'-(oxalylbis(azanediyl))dibenzoic acid (3-OADAH2) was used as a linker for the first time. X-ray diffraction analysis shows that the MOFs possess two-dimensional (2D) structures and the layers interact with each other through hydrogen bonds. Co-, Zn-, and Cd-3-OADA exhibit an excellent CO2 adsorption capacity of 8.87 wt% (45.15 cm3/g), 8.40 wt% (42.76 cm3/g), and 7.93 wt% (40.37 cm3/g) at 273 K and 3.98 wt% (20.27 cm3/g), 4.74 wt% (24.15 cm3/g), 3.68 wt% (18.72 cm3/g) at 298 K under 1 bar with isosteric heat of adsorption values (Qst) of about 34, 25, and 33 kJ/mol, respectively. This work opens a new opportunity for the development of functionalized 2D-MOFs with high CO2 capture capacity.
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    An extensive comparative analysis of two MOF databases: high-throughput screening of computation-ready MOFs for CH4 and H2 adsorption
    (Royal Soc Chemistry, 2019) Erucar, Ilknur; N/A; N/A; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Altıntaş, Çiğdem; Avcı, Gökay; Harman, Hilal Dağlar; Azar, Ayda Nemati Vesali; Velioğlu, Sadiye; Keskin, Seda; Researcher; PhD Student; PhD Student; PhD Student; Researcher; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; 200650; 40548
    Computation-ready metal-organic framework (MOF) databases (DBs) have tremendous value since they provide directly useable crystal structures for molecular simulations. The currently available two DBs, the CoRE DB (computation-ready, experimental MOF database) and CSDSS DB (Cambridge Structural Database non-disordered MOF subset) have been widely used in high-throughput molecular simulations. These DBs were constructed using different methods for collecting MOFs, removing bound and unbound solvents, treating charge balancing ions, missing hydrogens and disordered atoms of MOFs. As a result of these methodological differences, some MOFs were reported under the same name but with different structural features in the two DBs. In this work, we first identified 3490 common MOFs of CoRE and CSDSS DBs and then performed molecular simulations to compute their CH4 and H-2 uptakes. We found that 387 MOFs result in different gas uptakes depending on from which DB their structures were taken and we identified them as problematic' MOFs. CH4/H-2 mixture adsorption simulations showed that adsorbent performances of problematic MOFs, such as selectivity and regenerability, also significantly change depending on the DB used and lead to large variations in the ranking of materials and identification of the top MOFs. Possible reasons of different structure modifications made by the two DBs were investigated in detail for problematic MOFs. We described five main cases to categorize the problematic MOFs and discussed what types of different modifications were performed by the two DBs in terms of removal of unbound and bound solvents, treatment of missing hydrogen atoms, charge balancing ions etc. with several examples in each case. With this categorization, we aimed to direct researchers to computation-ready MOFs that are the most consistent with their experimentally reported structures. We also provided the new computation-ready structures for 54 MOFs for which the correct structures were missing in both DBs. This extensive comparative analysis of the two DBs will clearly show how and why the DBs differently modified the same MOFs and guide the users to choose either of the computation-ready MOFs from the two DBs depending on their purpose of molecular simulations.
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    Molecular simulations of porous coordination network-based mixed matrix membranes for CO2/N2 separations
    (Taylor & Francis Ltd, 2015) N/A; Department of Chemical and Biological Engineering; Altıntaş, Çiğdem; Keskin, Seda; Researcher; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 40548
    In this study, the challenge of selecting porous coordination networks (PCNs) as filler particles in mixed matrix membranes (MMMs) was examined using molecular simulations. PCNs are promising nanoporous materials in gas separations because of their tunable pore sizes, high porosities, good thermal and mechanical stabilities. Gas permeability and selectivity of 200 new MMMs composed of 20 different PCNs and 10 different polymers were calculated for CO2/N-2 separation. We showed that selecting the appropriate PCN as filler particles in polymers results in MMMs that have high CO2/N-2 selectivities and high CO2 permeabilities compared with pure polymer membranes. Several PCN/polymer MMMs were identified to exceed the upper bound established for CO2/N-2 separation. Effect of framework flexibility of PCNs on the performance of MMMs was also examined. Results showed that considering the flexibility of PCNs is important for predicting gas permeability of pure PCNs but has less significance for predicting gas permeability of PCN-filled MMMs whenever the PCN volume fraction is low. For rapid screening of PCN/polymer MMMs, flexibility of the fillers can be neglected as a reasonable approximation if the filler volume fraction is <0.3. The methods introduced in this study will create many opportunities for selecting PCN/polymer combinations for MMMs with useful properties in CO2 separation applications.
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    Improving gas separation performance of ZIF-8 by [BMIM][BF4] incorporation: interactions and their consequences on performance
    (Amer Chemical Soc, 2017) N/A; N/A; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Koyutürk, Burak; Altıntaş, Çiğdem; Kınık, Fatma Pelin; Keskin, Seda; Uzun, Alper; Master Student; Researcher; Master Student; Faculty Member; Faculty Member; 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); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; 40548; 59917
    Gas separation performance of the zeolitic imidazolate framework (ZIF-8) was improved by incorporating an ionic liquid (IL), 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). Detailed characterization based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed that the morphology of ZIF-8 remains intact upon IL incorporation up to 28 wt %. Thermogravimetric analysis indicated the presence of direct interactions between the IL and metal organic framework (MOF). FTIR spectroscopy illustrated that the anion of the IL was shared between the imidazolate framework and [BMIM](+) cation. Adsorption isotherms of CO2, CH4, and N-2 measured for pristine ZIF-8 and IL-loaded ZIF-8 samples, complemented by grand canonical Monte Carlo (GCMC) simulations, showed that these interactions influence the gas uptake performance of ZIF-8. CH4 and N-2 uptakes decreased in the whole pressure range, while CO2 uptake first increased by approximately 9% at 0.1 bar in 20 wt % IL-loaded sample and then decreased as in the case of other gases. As a result of these changes in gas uptakes different extents, the corresponding CO2/CH4, CO2/N-2, and CH4/N-2 selectivities were enhanced especially at the low-pressure regime upon IL incorporation. Results showed that CO2/CH4 selectivity increased from 2.2 to 4; while CO2/N-2 selectivity more than doubled from 6.5 to 13.3, and CH4/N-2 selectivity improved from 3 to 3.4 at 0.1 bar at an IL loading of 28 wt %. The heat of adsorption values (Q(st)) measured and simulated for each gas on each sample indicated that interactions between the IL and ZIF-8 strongly influence the gas adsorption behaviors. The change in Q(st) of CO2 upon IL incorporation was more significant than that of other gases, leading to an almost doubling of CO2 selectivity over CH4 and N-2, specifically at low pressures. On the other hand, the selectivity improvement was lost at high pressures because of a strong decrease in the available pore space due to the presence of IL in ZIF-8. These results suggest that such IL/MOF combinations with tunable structures have huge potential toward high performance gas separation applications.
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    Computational screening of MOFs for C2H6/C2H4 and C2H6/CH4 separations
    (Elsevier, 2016) N/A; Department of Chemical and Biological Engineering; Altıntaş, Çiğdem; Keskin, Seda; Researcher; Faculty Member; Department of Chemical and Biological Engineering; N/A; College of Engineering; N/A; 40548
    Metal organic frameworks (MOFs) are promising nanoporous materials in gas separation applications due to their tunable pore sizes, large surface areas, high porosities, good thermal and mechanical stabilities. In this study, large-scale computational screening of 278 different MOFs was performed for separation of C2H6/C2H4 and C2H6/CH4 mixtures using molecular simulations. This is the largest number of MOFs screened in the literature for these two gas separations. We first compared simulated gas adsorption data with the experimental measurements to validate the accuracy of our computational approach. Molecular simulations were then used to estimate adsorption selectivity, working capacity and sorbent selection parameter of MOFs for C2H6/C2H4 and C2H6/CH4 separations. Results showed that there is a significant number of MOFs predicted to exhibit significantly higher adsorption selectivities and working capacities compared to zeolites. Membrane selectivities of MOFs that show the highest adsorption selectivities were also calculated and compared with selectivities and gas permeabilities of zeolite and polymer membranes. Results show that MOFs can be strong alternatives to traditional membranes for C2H6/C2H4 separations. (C) 2015 Elsevier Ltd. All rights reserved.