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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 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 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 A water-soluble Irgacure 2959-based diallylammonium salt system for antibacterial coatings(Wiley, 2024) Balaban, Burcu; Avci, Duygu; Department of Chemistry; Güner, Pınar Tatar; Acar, Havva Funda Yağcı; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of SciencesA water-soluble mixture of a novel diallylammonium salt photoinitiator based on 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (Irgacure 2959 or I2959) and diallylammonium tosylate has been prepared. It shows excellent water-solubility of 6.8 wt% in water, much greater than the solubility of I2959 (<2 wt%). It has a strong absorbance at 269 nm (epsilon similar to 15731) in methanol. It exhibits 15.6 times higher migration stability than I2959 due to its monomeric nature. Its photoinitiating efficiency of 2-hydroxyethylmethacrylate (HEMA) and poly(ethylene glycol) diacrylate (PEGDA, M-n = 575 D) was found to be similar to I2959. PEGDA hydrogels prepared using the synthesized photoinitiator (PI) were found to have highly porous structures (15.44 mu m) compared with those using I2959. PEGDA film prepared using this PI has demonstrated antibacterial properties against gram-negative Pseudomonas aeruginosa (ATCC 15442) and gram-positive Staphylococcus aureus (ATCC 23235) bacterial species.Publication Metadata only Immune compatibility of 2D bismuthene nanosheets for future combined magnetic hyperthermia and photothermal therapy(Mary Ann Liebert, Inc, 2023) Giro, Linda; Gurcan, Cansu; Gazzi, Arianna; Ekim, Okan; Ceylan, Ahmet; Unal, Mehmet Altay; Ari, Fikret; Cinar, Ozge Ozgenc; Besbinar, Omur; Yilmazer, Acelya; Delogu, Lucia Gemma; Department of Chemistry; Eroğlu, Zafer; Sündü, Buse; Metin, Önder; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM); College of Sciences; Graduate School of Sciences and EngineeringPublication Metadata only Modification of tetrahedrite Cu12Sb4S13 thermoelectric performance via the combined treatment of mechanochemistry and composite formation(Elsevier Masson S.R.L., 2024) Baláž, Peter; Mikula, Andrzej; Nieroda, Pawel; Baláž, Matej; Findoráková, Lenka; Bureš, Radovan; Puchý, Viktor; Erdemoğlu, Murat; Achimovičová, Marcela; Guilmeau, Emmanuel; Bacha, Sandy Al; Department of Chemistry; Burçak, Arda Baran; Aydemir, Umut; Department of Chemistry; College of SciencesTetrahedrite Cu12Sb4S13 with its low thermal conductivity represents a flagship in sulphide thermoelectrics. However, to achieve a reasonable figure-of-merit ZT (measure of thermoelectric efficiency), adequate doping or special sample processing is needed. In this work, a different approach (without doping) is illustrated for the two tetrahedrite-containing systems. In the first approach binary composite tetrahedrite Cu12Sb4S13/chalcopyrite CuFeS2 was prepared by mechanochemical leaching with the aim to obtain partly decomposed tetrahedrite. In this approach, the alkaline leaching medium (Na2S + NaOH) was applied to extract Sb from tetrahedrite thus changing its composition. The obtained composite (formed from its own phases in an intrinsic mode) shows low values of ZT = 0.0022@673 K in comparison with the non-treated tetrahedrite where ZT was 0.0090@673 K. In this case the extremely high electric resistivity (6–20 mΩ cm−1) was documented. In the second approach binary composite tetrahedrite Cu12Sb4S13/muscovite KAl2(AlSi3O10)(OH)2 (formed from its own and foreign phases in an extrinsic mode) was prepared by two-step mechanical activation in which combined treatment of industrial vibratory milling and subsequent laboratory planetary milling was applied. The addition of a foreign phase, muscovite, did not give extraordinary thermoelectric performance results. However, the two-step milling process (without the addition of foreign phase) gives the value of ZT = 0.752@673 K which belongs to the highest in the tetrahedrite thermoelectric community. In this case, the two-times increase in specific surface area and the increased amount of tetrahedrite in comparison to famatinite are suspectable for this effect. Both applied non-traditional approaches to synthesize tetrahedrite composites form a platform for potential modification of its thermoelectric performance. © 2024 The AuthorsPublication Metadata only Control of heparin surface density in multilayers of partially hydrolyzed poly(2-ethyl-2-oxazoline) by degree of hydrolysis(Wiley, 2024) Department of Chemistry; Saadatlou, Ghazaleh Azizi; Güner, Pınar Tatar; Demirel, Adem Levent; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of SciencesControlling the surface density of heparin in active coatings is important in providing anticoagulation while preventing bleeding. An approach based on tuning the degree of hydrolysis of poly(2-ethyl-2-oxazoline) (PEOX) is presented to control the surface density of heparin in layer-by-layer (LbL) assembled films. Multilayers are prepared at pH 5 in 0.5 M aqueous NaCl solutions by electrostatic interactions between negatively charged heparin and the positively charged amine groups in hydrolyzed PEOX. Characterization of the multilayers by quartz crystal microbalance with dissipation (QCM-D), toluidine blue (TBO) assay and X-ray Photoelectron Spectroscopy (XPS) all shows that the amount of heparin deposited increases with the degree of hydrolysis. While non-hydrolyzed PEOX/heparin multilayers do not grow, the average deposited mass per area per bilayer as determined by QCM-D measurements increases with the degree of hydrolysis. At 50% hydrolysis, TBO assay gives a heparin surface density of 1.03 mu g/cm(2) and atomic % of sulfur as determined by XPS leveled off at similar to 14%. These results show the potential of acidic hydrolysis of PEOX combined with LbL assembly of heparin as a reproducible method for controlling the surface density of heparin in anticoagulant coatings.Publication Metadata only Step-edge decoration and clustering of Pt atoms on a Cu(211) stepped surface(Amer Chemical Soc, 2024) Department of Chemistry; Mohammadpour, Amin; Kaya, Sarp; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of SciencesThe atomic manipulation of the low-coordination sites of metal catalysts can give rise to activity enhancement;however, it is rather challenging to locally probe the dynamic changes and activities of these sites. Herein, step-edge/terrace site decoration and site exchange of Pt atoms with a stepped Cu(211) surface were investigated by a combination of infrared reflection absorption spectroscopy (IRRAS) and temperature-programmed desorption (TPD) of carbon monoxide (CO). For a low coverage of Pt, step decoration and site exchange with Cu were found to be two pathways to isolate Pt as single atoms. CO preferentially adsorbs near the Cu step sites on the lower terrace, and the binding energies of CO show strong Pt coverage dependence. The presence of Pt on terrace and step sites modifies the binding energy of CO absorbed on Cu in the proximity. Increased Pt-Pt lateral coordination changes the site preference;however, the reduced binding energy of CO to Pt is attributed to heteroatom bond formation rather than the strain induced by the lattice mismatch.Publication Metadata only Layer-by-layer assembly of Chitosan and Quince seed gum polyelectrolytes as a pH-responsive, on-off switchable multilayer film for controlled release of Ibuprofen(ELSEVIER, 2024) Kaviani, Alireza; Pircheraghi, Gholamreza; Bagheri, Reza; Department of Chemistry; Saadatlou, Ghazaleh Azizi; Demirel, Adem Levent; Department of Chemistry; Graduate School of Sciences and Engineering; College of SciencesPolysaccharide-based multilayer films have shown substantial potential for drug delivery applications. In the meantime, researchers have been captivated by Quince seed gum (QSG) with a high content of acidic polysaccharides because of its versatile responsiveness to salts, pH, and solvents. Accordingly, polyelectrolyte multilayers using Chitosan (CS) and Quince seed gum (QSG) were constructed and the effects of assembly pH, salt concentration, and post-assembly pH were systematically investigated. It was evident that both mass per unit area (10,000 ng/cm2) and the wet thickness (107.8 nm) after the deposition of 5 bilayers were accurately estimated by the viscoelastic model due to the highly swollen state of films. Atomic force microscopy could feasibly demonstrate the development of globular structures during the layer-by-layer assembly. Ellipsometry analysis showed that the variation of assembly pH resulted in conformational changes from extended to coiled. Consequently, different optical thicknesses as well as transitions from exponential to linear growth were observed. Moreover, extrinsic charge compensation was responsible for coiling or extensive counterion screening of polyelectrolyte chains depending on the NaCl concentration. CS/QSG films displayed pH-stimulus responsive on-off switching behavior at pH 2 and 7.4 for 3 cycles. The constructed film could absorb 1200 ng/cm2 Ibuprofen within 60 min at pH 7.4. The in vitro release kinetics from Ibuprofen-loaded samples showed pH dependency. The CS/QSG multilayer film can be considered as a smart pH tunable system for drug loading/release applications.Publication Metadata only Nitrogen-based imperfections in graphitic carbon nitride - new trend for enhancing photocatalytic activity?(Wiley, 2024) Department of Chemistry; Eroğlu, Zafer; Özer, Melek Sermin; Metin, Önder; Department of Chemistry; College of SciencesThis review comprehensively explores the engineering of nitrogen vacancies (N-vacancies) in polymeric carbon nitride (CN) and uncovering their profound impact on the photocatalytic applications of CN. The intentional creation of N-vacancies in CN obtained by removing the targeted N atoms emerges as a crucial strategy for fine-tuning its photo(catalytic)physical properties. Defect-centric investigations illuminate enlarged surface areas, increased substrate interactions and spotlight the correlation between N-vacancy and photoredox transformations. Key N-vacancies (NHx, N2C, N3C) play exceptional roles in elevating the photocatalytic activity of CN. Besides comprehensively navigating the competitive literature of CN research, this review highlights the controlled manipulation of N-vacancies in CN as an instrumental avenue for customized property tailoring. Additionally, it provides a perspective on the generation of N-vacancies considering temperature, time, and reaction atmosphere by inspecting available synthesis strategies, particularly thermal treatments, along with advanced characterization techniques shedding light on the profound influence of N-vacancies on the structural and electronic properties of CN. Moreover, this review underlines the impact of defects in CN on its photocatalytic performance, tuning bandgaps, midgap state formation, and creating active sites within the lattice. The versatile strategy employed in vacancy engineering within CN shows great potential for designing new-generation photocatalysts with tailored functionalities. This review provides a perspective for researchers in the relevant field by depicting the challenges, providing an insightful perspective, and exploring future directions aimed at catalyzing advances in the field of N-vacancy CN for various photocatalytic applications.