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Department: search.filters.department.Department of Chemical and Biological EngineeringSubject: search.filters.subject.Physics

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    High-throughput computational screening of MOF adsorbents for efficient propane capture from air and natural gas mixtures
    (AIP Publishing, 2024) Department of Chemical and Biological Engineering; Erçakır, Göktuğ; Aksu, Gökhan Önder; Keskin, Seda; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering
    In this study, we used a high-throughput computational screening approach to examine the potential of metal-organic frameworks (MOFs) for capturing propane (C3H8) from different gas mixtures. We focused on Quantum MOF (QMOF) database composed of both synthesized and hypothetical MOFs and performed Grand Canonical Monte Carlo (GCMC) simulations to compute C3H8/N2/O2/Ar and C3H8/C2H6/CH4 mixture adsorption properties of MOFs. The separation of C3H8 from air mixture and the simultaneous separation of C3H8 and C2H6 from CH4 were studied for six different adsorption-based processes at various temperatures and pressures, including vacuum-swing adsorption (VSA), pressure-swing adsorption (PSA), vacuum-temperature swing adsorption (VTSA), and pressure-temperature swing adsorption (PTSA). The results of molecular simulations were used to evaluate the MOF adsorbents and the type of separation processes based on selectivity, working capacity, adsorbent performance score, and regenerability. Our results showed that VTSA is the most effective process since many MOFs offer high regenerability (>90%) combined with high C3H8 selectivity (>7 x 103) and high C2H6 + C3H8 selectivity (>100) for C3H8 capture from air and natural gas mixtures, respectively. Analysis of the top MOFs revealed that materials with narrow pores (<10 angstrom) and low porosities (<0.7), having aromatic ring linkers, alumina or zinc metal nodes, typically exhibit a superior C3H8 separation performance. The top MOFs were shown to outperform commercial zeolite, MFI for C3H8 capture from air, and several well-known MOFs for C3H8 capture from natural gas stream. These results will direct the experimental efforts to the most efficient C3H8 capture processes by providing key molecular insights into selecting the most useful adsorbents.
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    Gas adsorption and diffusion in a highly CO2 selective metal-organic framework: molecular simulations
    (Taylor and Francis Ltd, 2013) N/A; Department of Chemical and Biological Engineering; Keskin, Seda; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 40548
    Grand canonical Monte Carlo and equilibrium molecular dynamics simulations were used to assess the performance of an rht-type metal–organic framework (MOF), Cu-TDPAT, in adsorption-based and membrane-based separation of CH4/H2, CO2/CH4 and CO2/H2 mixtures. Adsorption isotherms and self-diffusivities of pure gases and binary gas mixtures in Cu-TDPAT were computed using detailed molecular simulations. Several properties of Cu-TDPAT such as adsorption selectivity, working capacity, diffusion selectivity, gas permeability and permeation selectivity were computed and compared with well-known zeolites and MOFs. Results showed that Cu-TDPAT is a very promising adsorbent and membrane material especially for separation of CO2 and it can outperform traditional zeolites and MOFs such as DDR, MFI, CuBTC, IRMOF-1 in adsorption-based CO2/CH4 and CO2/H2 separations.
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    Predicting water solubility in ionic liquids using machine learning towards design of hydro-philic/phobic ionic liquids
    (Elsevier, 2021) Can, Elif; Zirhlioglu, I. Gulcin; Yildirim, Ramazan; N/A; Department of Chemical and Biological Engineering; Jalal, Ahsan; Uzun, Alper; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 59917
    In this work, a database containing the solubility data for water in 16,137 ionic liquids (ILs), which were formed by a combination of the most commonly used 163 cations (in nine groups) and 99 anions, were analyzed using machine learning. The water solubility in ILs was computed by COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) while the molecular descriptors for the individual cations and anions were determined by semi-empirical PM3 method. Association rule mining, decision tree and multilayer fully connected neural network (a deep learning model) were employed as machine learning techniques. The association rule mining analysis clearly identified the descriptors leading to low water solubility in ILs, while the decision tree analysis provided heuristic rules for the selection of cations and anions to form ILs with low water capacity. The prediction accuracy of fully connected neural network model was also high; even the model constructed from a small fraction of data was successful to predict the water solubility in other ILs in the dataset indicating that the anionic and cationic descriptors used were sufficient to represent the performance of ILs. The classification ability of decision trees was verified by the experimental water solubility data for 49 ILs extracted from 13 published papers in literature; the decision tree model correctly classified the experimental solubility of 46 of these ILs. The deep learning predictions of solubility were also in agreement with the experimental data within the accuracy level of COSMO-RS calculations. It was generally found that the anionic descriptors were more influential to predict the water capacity of ILs, while the cationic descriptors made limited contribution.
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    Development of highly stable and luminescent aqueous CdS quantum dots with the poly(acrylic acid)/mercaptoacetic acid binary coating system
    (Amer Scientific Publishers, 2009) Lieberwirth, I.; Department of Chemistry; N/A; Department of Chemical and Biological Engineering; Acar, Havva Funda Yağcı; Çelebi, Serdar; Serttunalı, Nazlı İpek; Faculty Member; Master Student; Undergraduate Student; Department of Chemistry; Department of Chemical and Biological Engineering; College of Sciences; Graduate School of Sciences and Engineering; College of Engineering; 178902; N/A; N/A
    Highly stable and luminescent CdS quantum dots (QD) were prepared in aqueous solutions via in situ capping of the crystals with the poly(acrylic acid) (PAA) and mercaptoacetic acid (MAA) binary mixtures. The effect of reaction temperature and coating composition on the particle size, colloidal stability and luminescence were investigated and discussed in detail. CdS QDs coated with either PAA or MAA were also prepared and compared in terms of properties. CdS-MAA QDs were highly luminescent but increasing reaction temperature caused an increase in the crystal size and a significant decrease in the quantum yield (QY). Although less luminescent and bigger than CdS-MAA, CdS-PAA QDs maintained the room temperature size and QY at higher reaction temperatures. CdS-MAA QDs lacked long term colloidal stability whereas CdS-PAA QDs showed excellent stability over a year. Use of PAA/MAA mixture as a coating for CdS nanoparticles during the synthesis provided excellent stability, high QY and ability to tune the size and the color of the emission. Combination of all of these properties can be achieved only with the mixed coating. CdS coated with PAA/MAA at 40/60 ratio displayed the highest QY (50% of Rhodamine B) among the other compositions.
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    Thermal stability limits of imidazolium, piperidinium, pyridinium, and pyrrolidinium ionic liquids immobilized on metal oxides
    (Elsevier, 2022) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Öztulum, Samira Fatma Kurtoğlu; Jalal, Ahsan; Uzun, Alper; PhD Student; PhD Student; 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; College of Engineering; 384798; N/A; 59917
    Twenty-nine different ionic liquids (ILs) consisting of imidazolium, pyridinium, piperidinium, and pyrro-lidinium cations and I-, Cl-, Br-, PF6-, BF4-, [DCA]-, and [NTf2]- anions were immobilized on MgO and SiO2. Their short-term thermal stability limits were investigated by thermogravimetric analysis and compared with those of the corresponding bulk ILs. Data showed that the thermal stability limits of ILs change sig-nificantly when the ILs are immobilized on metal oxides. These changes were evaluated based on the structural interactions determined by infrared (IR) spectroscopy. Systematic structural differences were considered to investigate the factors affecting the thermal stability of bulk ILs, and their counterparts immobilized on MgO and SiO2. These structural changes were the change in the alkyl chain length, the methylation on C2 site in imidazolium ILs, the change in substituent position in the pyridinium ring, the change in the anion, and the change in the IL family. The strongest factor controlling the thermal sta-bility limits of both bulk ILs and their supported counterparts was determined as the anion type. Accordingly, the basicity of the anion and the surface acidity of the metal oxide and their resulting inter-actions were found to have a significant effect on the thermal stability limits. Data presented here offer the opportunity to pick a suitable anion and cation pair according to the metal oxide, so that the sup-ported IL can withstand the desired operation conditions in various applications, such as catalysis or gas separation.
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    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; 280298
    The 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.
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    Recent Advances in Molecular Dynamics Simulations of Gas Diffusion in Metal Organic Frameworks
    (Intech Europe, 2012) N/A; Department of Chemical and Biological Engineering; Keskin, Seda; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 40548
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    Enhancing biocompatibility of NiTi shape memory alloys by simple NH3 treatments
    (Elsevier, 2020) N/A; N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Mechanical Engineering; Öztulum, Samira Fatma Kurtoğlu; Yağcı, Mustafa Barış; Uzun, Alper; Ünal, Uğur; Canadinç, Demircan; PhD Student; Researcher; Faculty Member; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Mechanical 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; N/A; College of Engineering; College of Sciences; College of Engineering; 384798; N/A; 59917; 42079; 23433
    This paper presents the treatment of NiTi shape memory alloys (SMAs) in flowing ammonia at 700 degrees C as a simple and cost-effective nitriding process to provide a protective surface layer hindering Ni ion release in biological environments. Experimental results demonstrated that a smooth protective TiN layer on the NiTi SMAs along with TiOxNy and TiO2 formed on the surface upon treating the as-received NiTi SMA in ammonia at 700 degrees C. The protective TiN layer and the smooth surface hinder the amount of Ni ion release to artificial saliva (AS) after 28 days of immersion, while the dry air treatment at similar conditions results in a significantly rough surface, leading to about 20 times higher Ni ion release. Overall, the findings presented herein demonstrate that NH3 nitriding is an effective method to eliminate the Ni presence from the surface and to obtain a smooth final surface, which, in turn, restricts the Ni ion release from the NiTi SMA into AS. Consequently, nitriding the surface of NiTi under NH3 at 700 degrees C turned out as a promising method to lower Ni ion release and thereby contribute to the biocompatibility of NiTi SMAs, which, however; needs to be further validated through further experimentation.
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    Selection rules for estimating the solubility of C4-hydrocarbons in imidazolium ionic liquids determined by machine-learning tools
    (Elsevier, 2019) Can, Elif; Yıldırım, Ramazan; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Jalal, Ahsan; Keskin, Seda; Uzun, Alper; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; 40548; 59917
    Solubilities of C-4-hydrocarbons, 1,3-butadiene (13BD), trans/cis-2-butene (T2B and C2B), 1-butene (1B), isobutene (i-But), isobutane (i-B), and butane (B), in 3267 different imidazolium-type ionic liquids (ILs) in a temperature range from 273.15 to 373.15 K were estimated by means of the COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) calculations. Simple temperature-dependent mathematical expressions were developed to predict the solubility of 13BD, C2B, T2B, 1B, i-But, i-B, and B at any temperature in a range from 273 to 373 K. The COSMO-RS results for each hydrocarbon considered were then analyzed using machine learning tools, induding association rule mining and decision tree classification, using semi-empirically derived molecular descriptors of ILs. It was found that the polarizabilities of both cation and anion, together with the anion's CPK (space filling model) area, are the most important descriptors for determining the affinity of ILs towards C-4-hydrocarbons. Results also present the selection rules for imidazolium ILs, offering opportunities for the rational design of new ILs by using these simply-determined structural descriptors to meet the desired solubility (or selectivity) requirements for each C-4-hydrocarbon considered.
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    Two novel 2D and 3D coordination polymers constructed from pyrazine-2,3-dicarboxylic acid and chloride bridged secondary building units
    (Elsevier Science Sa, 2011) Gunay, Gunes; Yesilel, Okan Zafer; Soylu, Mustafa Serkan; Dal, Hakan; Department of Chemical and Biological Engineering; Keskin, Seda; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 40548
    The synthesis, spectroscopic properties and crystal structures of {[Cu-2(mu-Cl)(2)(mu(3)-Hpzdc)(Cl)(H2O)(2)]center dot 1.5H(2)O}(n) (1) and {[Cd(mu-Cl)(mu-Hpzdc)]center dot H2O)}(n) (2) complexes were reported (H(2)pzdc = pyrazine-2,3-dicarboxylic acid). H(2)pzdc is singly deprotonated in both complexes and the coordination mode of Hpzdc ligand in 1 has been first reported in this presentation. The complex 1, which has a 3D framework structure, was formed with double mu-chloride and mu(3)-Hpzdc bridges. In 1, water molecules occupy in the 1D channel as guest molecules. Furthermore, unprecedented 1D hybrid water-chloride anionic [(H2O)(8)Cl-2](n) cluster has been structurally identified. In the complex 2, the Cd(II) atom is seven-coordinated by two hydrogen pyrazine-2,3-dicarboxylate, two chloride and one aqua ligands in a distorted monocapped octahedral coordination geometry. The Cd(II) atoms are bridged by the bis(bidentate) Hpzdc ligands, forming 1D polymer chain. The adjacent 10 chains are linked each other through the double chloride bridges to form 20 layer. The layers are connected together through O-H center dot center dot center dot O interactions resulting in a three-dimensional framework. The mechanisms for these compounds were validated by density functional theory (DFT) calculations on the experimental geometries. The photoluminescent property of 2 was investigated in the solid state at room temperature. Moreover, in order to assess the potentials of 1 and 2 in gas storage applications, we performed atomically detailed simulations.