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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Tracing the phase formation and stability of the clathrate phase BaGe5(Elsevier Inc., 2024) Baitinger, Michael; Grin, Yuri; Burkhardt, Ulrich; Department of Chemistry; Aydemir, Umut; 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 SciencesThermal stability and phase formation of the clathrate phase BaGe5 and its formation from the clathrate-I phase Ba8Ge43 square(3) (square = vacancy in the crystal structure) have been investigated by microstructure analysis, differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD). The experiments confirm the peritectic formation of the high-temperature phase Ba8Ge43 square(3) from alpha-Ge and liquid at 810 degrees C, and the eutectic temperature of Ba8Ge43 square(3) and Ba6Ge25 at 808 degrees C. At T = 770 degrees C, Ba8Ge43 square(3) decomposes by a eutectoid reaction to Ba6Ge25 and alpha-Ge, and at T = 520 degrees C, the low-temperature phase BaGe5 forms in a peritectoid reaction from these two phases. BaGe5 was synthesized by decomposition of the high-temperature clathrate-I phase Ba8Ge43 square(3) at temperatures between 350 degrees C and 520 degrees C. Annealing and DSC experiments verify that BaGe5 is an equilibrium phase at ambient pressure. The formation of BaGe5 from Ba8Ge43 square(3) was traced through microstructure analysis, revealing microdomains with pleochroic behavior in polarized light.Publication Metadata only Photocatalytic performance of disordered titanium-based hollow nanosheet metal-organic frameworks in wastewater treatment(Elsevier, 2024) Hassandoost, Ramin; Khataee, Alireza; Department of Chemistry; Doustkhah, Esmail; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of SciencesBackground: The low long-range order in the crystallinity of metal-organic frameworks (MOFs), commonly known as disordered MOFs, can lead to critical property variations. However, controlling the synthesis conditions for a reproducible outcome is somehow cumbersome, especially if this control is accompanied by morphology engineering to be utilized in photocatalysis where band structure, band gap, surface area, and porosity matter. Methods: Here, we report a crystal and structure-directing approach for the morphology engineering of NTU-9-like MOF aggregated particles (Ti-DHTA(AP)) (composed of Ti4+ and 2,5-dihydroxyterephthalic acid (DHTA)) into a hollow nanosheet (Ti-DHTA(HNS)) morphology. Triethylamine (TEA), here, acts as a structure-directing agent (SDA), and monodispersed polystyrene (PS) as a hard template. The three obtained Ti-DHTAs were eventually investigated in the photocatalytic removal of organic contaminants (dye and pharmaceuticals) and comprehensively characterized by (photo)electrochemical approaches. Significant Findings: The hollow nanosheet-architected Ti-DHTA(HNS) with a superior photocatalytic activity than the other morphologies also exhibits an overall photocatalytic removal (synergic adsorption-photodegradation) of similar to 6.5-fold higher than the commercial TiO2 (P25) under the visible light irradiation, with a degradation turnover (dTON) of 27 mmol h(-1) g(cat)(-1). Ti-DHTA(HNS) also shows promising results in the photocatalytic removal of dye and pharmaceutical wastewater. Photoelectrocatalytic characterizations were provided to compare the photocatalytic performance of synthesized Ti-DHTAs (e.g., in cyclic chronoamperometry (CA), 6-fold higher photoresponse than Ti-DHTA(AP)). Nyquist plots further exhibit that the charge transfer resistance (R-ct) of the unmodified Ti-DHTA(AP) is similar to 10-fold higher than Ti-DHTA(HNS) under visible light illumination. Furthermore, the actual water samples and the reusability of Ti-DHTA(HNS) were investigated. The addition of the radical scavenger agent can confirm the presence of varoius active radicals during the degradation, and hence, the formation of hydroxyl radicals was probed by adding o-phenylenediamine as a trapping agent. During methylene blue (MB) photodegradation, the LC-MS analysis exhibits acetoacetic acid formation (m/z = 102.03) as the dominant intermediate.Publication Metadata only Collision-induced state-changing rate coefficients for cyanogen backbones NCN 3Σ− and CNN 3Σ− in astrophysical environments(Royal Society of Chemistry, 2023) González-Sánchez, Lola; de la Fuente, Jorge Alonso; Sanz-Sanz, Cristina; Wester, Roland; Gianturco, Francesco A.; Department of Chemistry; Department of Chemistry; College of SciencesWe report quantum calculations involving the dynamics of rotational energy-transfer processes, by collision with He atoms in interstellar environments, of the title molecular species which share the presence of the CN backbone and are considered of importance in those environments. The latter structural feature is taken to be especially relevant for prebiotic chemistry and for its possible role in the processing of the heterocyclic rings of RNA and DNA nucleobases in the interstellar space. We carry out ab initio calculations of their interaction potentials with He atoms and further obtain the state-to-state rotationally inelastic cross sections and rate coefficients over the relevant range of temperatures. The similarities and differences between such species and other similar partners which have been already detected are analyzed and discussed for their significance on internal state populations in interstellar space for the two title molecular radicals.Publication Metadata only Three-body collisions driving the ion-molecule reaction c 2-+ h2 at low temperatures(Amer Chemical Soc, 2023) Lochmann, Christine; Notzold, Markus; Wild, Robert; Satta, Mauro; Gianturco, Francesco A.; Wester, Roland; Department of Chemistry; Department of Chemistry; College of SciencesWe report on the three-body reaction rate of C-2- with H-2 producing C2H- studied in a cryogenic 16-pole radio frequency ion trap. The reaction was measured in the temperature range from 10 to 28 K, where it was found to only take place via three-body collisions. The experimentally determined termolecular rate coefficient follows the form of a center dot(T/T)b 0 with T0 = 20 K, where a = 8.2(3) x 10(-30) cm(6)/s and b = -0.82(12) denotes the temperature dependence. We additionally performed accurate ab initio calculations of the forces between the interacting partners and carried out variational transition state theory calculations, including tunneling through the barrier along the minimum energy path. We show that, while a simple classical model can generally predict the temperature dependence, the variational transition state theoretical calculations, including accurate quantum interactions, can explain the dominance of three-body effects in the molecular reaction mechanism and can reproduce the experimentally determined reaction coefficients, linking them to a temperature-dependent coupling parameter for energy dissipation within the transition complex.Publication Metadata only Rotational state-changes in C5N− by collisions with He and H2(Oxford University Press, 2023) Biswas,R.; Giri,K.; González-Sánchez,L.; Gianturco,F.A.; Lourderaj,U.; Sathyamurthy,N.; Veselinova,A.; Wester,R.; Department of Chemistry; Department of Chemistry; College of SciencesThe anion C5N− is one of the largest linear (C, N)-bearing chains detected in the interstellar medium. Here we present and discuss the general features of new ab initio potential energy surfaces describing the interaction of this linear anion with He and H2. We employ a Legendre Polynomials expansion representation for the former and an artificial neural network fit for the latter. We then carry out quantum scattering calculations to yield rotationally inelastic cross-sections for collisions with He and H2, using relative translational energy values in the range of 0.1-300 cm−1. We then obtained the corresponding inelastic rate coefficients as a function of temperature covering the range from 1 to 100 K. The results for these two systems are compared with each other, as well as with the earlier results on the C3N− colliding with the same partners. We found that the final inelastic rate coefficients for this anion are all fairly large, those from collisions with H2 being the largest. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are discussed in our conclusions.Publication Metadata only Solar-light-driven photocatalytic hydrogen evolution activity of gCN/WS2 heterojunctions incorporated with the first-row transition metals(Elsevier Science Sa, 2023) Acar, Eminegul Genc; Aslan, Emre; Patir, Imren Hatay; Department of Chemistry; Yılmaz, Seda; Eroğlu, Zafer; Metin, Önder; Department of Chemistry; 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 SciencesThe design of semiconductor-based heterojunctions is an effective strategy to build highly active photo-catalyst systems. In this study, tungsten disulfide (WS2) modified graphitic carbon nitride (gCN) hetero-junction (gCN/WS2) is incorporated with Co and Ni (gCN/WS2-Co and gCN/WS2-Ni) to enhance the photocatalytic hydrogen evolution reaction (HER) activity of gCN/WS2 via performing a chemical reduction method and characterized by advanced analytical techniques. The photocatalytic HER activities of gCN, gCN/ WS2, gCN/WS2-Ni and gCN/WS2-Co were measured as 0.126, 0.221, 0.237 and 0.249 mmol g-1h-1, respec-tively, under the visible light irradiation. The improvement of photocatalytic activity and stability of gCN/ WS2-Ni and gCN/WS2-Co nanocomposites could be attributed to the 2D/2D heterojunction structure, ex-tended light harvesting ability, increased electron-hole lifetime and decreased recombination rate of the charge carriers. Moreover, mechanistic studies revealed that a S-scheme heterojunction is attributed to the enhanced photocatalytic HER by the gCN/WS2-Ni and gCN/WS2-Co photocatalysts, which provides pro-moted efficiency by photocarrier transfer and separation.Publication Metadata only Black phosphorus/WS2-TM (TM: Ni, Co) heterojunctions for photocatalytic hydrogen evolution under visible light illumination(MDPI, 2023) Acar, Emineguel Genc; Çekceoglu, Ilknur Aksoy; Aslan, Emre; Patir, Imren Hatay; Department of Chemistry; Yılmaz, Seda; Eroğlu, Zafer; Metin, Önder; Department of Chemistry; 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 SciencesBlack phosphorus (BP) has recently emerged as a versatile photocatalyst owing to its unique photophysical properties and tunable bandgap. Nonetheless, the rapid recombination of the photogenerated charges of pristine BP samples has significantly hindered its practical applications in photocatalysis. Herein, we report, for the first time, the effect of transition metal nanoparticles (Ni and Co) as co-catalysts on the photocatalytic activity of BP/tungsten disulfide (WS2) binary heterojunctions (BP/WS2-TM (TM: Ni, Co)) in the hydrogen evolution reaction (HER) under visible light irradiation (& lambda; > 420 nm). Ternary heterojunctions named BP/WS2-TM (TM: Ni, Co) were synthesized via a chemical reduction method, leading to the formation of an S-scheme heterojunction, in which BP acts as a reduction catalyst and WS2 serves as an oxidation catalyst. BP/WS2-Ni and BP/WS2-Co performed substantial amounts of hydrogen generation of 9.53 mmol h(-1)g(-1) and 12.13 mmol h(-1)g(-1), respectively. Moreover, BP/WS2-Co exhibited about 5 and 15 times higher photocatalytic activity compared to the binary BP/WS2 heterojunctions and pristine BP, respectively. The enhanced photocatalytic activity of the heterojunction catalysts is attributed to the extended light absorption ability, enhanced charge separation, and larger active sites. This study is the first example of photocatalytic hydrogen evolution from water by using Ni- and Co-doped binary BP/WS2 heterojunctions.Publication Metadata only Influence of soft segment structure, hydrogen bonding, and diisocyanate symmetry on morphology and properties of segmented thermoplastic polyurethanes and polyureas(Tubitak Scientific & Technological Research Council Turkey, 2023) Department of Chemistry; Yılgör, Emel; Yılgör, İskender; Department of Chemistry; College of SciencesA comprehensive review of the structure-morphology-property relations in segmented thermoplastic polyurethanes and polyureas (TPU) is provided. Special emphasis is given to the influence of the soft segment structure, polarity, and molecular weight, diisocyanate symmetry and the nature, extent, and strength of hydrogen bonding on the morphology and thermal and mechanical properties of TPUs. Experimental results obtained on composition-dependent TPU morphology and properties by various techniques were also compared by the morphology profiles generated by computational methods such as quantum mechanical calculations and molecular dynamics simulations.Publication Metadata only Polyurethanes for elastomers(American Chemical Society, 2023) Department of Chemistry; Yılgör, Emel; Yılgör, İskender; Department of Chemistry; College of SciencesPolyurethanes consisting of hard and soft segments—chemically linked together with covalent bonds along a linear or crosslinked polymeric backbone—display mechanical properties ranging from soft elastomers to tough rubbers (depending on their chemical compositions), along with chain topologies and bulk morphologies. The availability of a wide selection of starting materials—with a large variety of physical and chemical properties—allows the tailoring of the design and synthesis of a very large number of linear, highly branched, and crosslinked polyurethane elastomers. In this chapter, preparation of polyurethane elastomers is discussed. This chapter also discusses the effects of various critical parameters, such as chemical composition, segment type, segment molecular weight, solubility parameters, and the nature and extent of hydrogen bonding on the morphology and properties of these materials. Although the focus will be on linear, segmented thermoplastic polyurethane/urea elastomers, this chapter also provides a discussion on the preparation and properties of hyperbranched and crosslinked polyurethane/urea elastomers.Publication Metadata only Meso-2,3-dimercaptosuccinic acid-based macromers for ph-sensitive degradable hydrogelsa(Amer Chemical Soc, 2023) Guven, Melek Naz; Demirci, Gozde; Avci, Duygu; Department of Chemistry; Acar, Havva Funda Yağcı; Department of Chemistry; College of SciencesOne way of tailoring the properties of hydrogels is using functional cross-linkers. In this study, four highly watersoluble and degradable carboxylated diacrylate and diacrylamide macromeric cross-linkers were designed as precursors to prepare pH-sensitive and degradable hydrogels. The macromers were synthesized from thiol-Michael addition reaction of meso-2,3dimercaptosuccinic acid (DMSA) with poly(ethylene glycol) diacrylate (PEGDA, M-n = 575 g/mol) or N,N '-methylene bis(acrylamide) (MBA) in the presence of triethyl amine or sodium hydroxide. They were used as cross-linkers in fabrication of 2-hydroxyethyl methacrylate (HEMA)-based hydrogels, whose swelling strongly depended on pH, macromer structure, and hydrogel composition. The degradabilities of the hydrogels were greatly enhanced by increasing the concentration of the cross-linkers. The mechanical properties of the hydrogels can be tuned by tailoring the cross-linking macromer. The hydrogels were proven to have metal chelating ability in the context of Fe3+ ions, and upon this chelation, Young's modulus was also observed to increase significantly. In vitro cytotoxicity evaluations against U-2 OS human bone osteosarcoma epithelial cells and C2C12 mouse myoblast cells showed that the PEGDA functional macromers are not toxic.