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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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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 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.Publication Metadata only Bulk MgB2 superconductor for levitation applications fabricated with boron processed by different routes(Elsevier Science Sa, 2023) Savaskan, B.; Ozturk, U. K.; Guner, S. B.; Abdioglu, M.; Bahadir, M. V.; Acar, S.; Ionescu, A. M.; Locovei, C.; Enculescu, M.; Badica, P.; Department of Chemistry; Somer, Mehmet Suat; Department of Chemistry; College of SciencesBulk MgB2 discs were prepared by an in situ route from mixtures of magnesium and boron powders. The boron powders were produced by two methods. The first one consisted of a self-propagating high tem-perature magnesiothermic synthesis (SHS) process followed by acid and fluorine cleaning and a heat treatment in inert atmosphere. This approach produced boron with purities between 86 % and 97 %, where the main impurity was Mg. Depending on the final heat treatment, these boron powders were amorphous or crystalline. In the second route, high purity nano powders (99 %) of boron were obtained by a diborane pyrolysis process. Bulks of MgB2 were characterized by structural, microstructural, and magnetic mea-surements. Critical current density, pinning force aspects and levitation force (including guiding force) details were assessed. Amorphous lower purity boron (86-97 %) obtained by the first processing route was found to promote the largest levitation forces of the MgB2 bulks and, among these samples, the best le-vitation results were recorded when using boron with a purity of 95-97 %. Use of a lower purity boron that decreases the cost of MgB2 promotes large scale production at industrial level of bulk MgB2 super-conducting magnets for levitation applications and enhances the applicability potential of MgB2 super-conductor. The relationship between levitation force and specific features of the samples such as pinning force details are discussed.Publication Metadata only Single-atom SN-loaded exfoliated layered titanate shows photocatalytic activity in hydrogen generation(NLM (Medline), 2023) Ide, Yusuke; Matsumoto, Hiroaki; Igarashi, Keisuke; Department of Chemistry; Üstünel, Tuğçe; Doustkhah, Esmail; 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 SciencesN/APublication 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 Optical imaging probes for selective detection of butyrylcholinesterase(Royal Soc Chemistry, 2024) Chan, Jefferson; Department of Chemistry; Dırak, Musa; Kölemen, Safacan; Department of Chemistry; Graduate School of Sciences and Engineering; College of SciencesButyrylcholinesterase (BChE), a member of the human serine hydrolase family, is an essential enzyme for cholinergic neurotransmission as it catalyzes the hydrolysis of acetylcholine. It also plays central roles in apoptosis, lipid metabolism, and xenobiotic detoxification. On the other side, abnormal levels of BChE are directly associated with the formation of pathogenic states such as neurodegenerative diseases, psychiatric and cardiovascular disorders, liver damage, diabetes, and cancer. Thus, selective and sensitive detection of BChE level in living organisms is highly crucial and is of great importance to further understand the roles of BChE in both physiological and pathological processes. However, it is a very complicated task due to the potential interference of acetylcholinesterase (AChE), the other human cholinesterase, as these two enzymes share a very similar substrate scope. To this end, optical imaging probes have attracted immense attention in recent years as they have modular structures, which can be tuned precisely to satisfy high selectivity toward BChE, and at the same time they offer real time and nondestructive imaging opportunities with a high spatial and temporal resolution. Here, we summarize BChE selective imaging probes by discussing the critical milestones achieved during the development process of these molecular sensors over the years. We put a special emphasis on design principles and biological applications of highly promising new generation activity-based probes. We also give a comprehensive outlook for the future of BChE-responsive probes and highlight the ongoing challenges. This collection marks the first review article on BChE-responsive imaging agents. Butyrylcholinesterase (BChE) is a human serine hydrolase, which plays critical roles in various physiological and pathological states. Here, we summarized the optical probes that can selectively monitor the BChE activity in different biological models.Publication Metadata only Understanding the role of additional Cu intercalation in electronic and thermal properties of p-type Cu2.9Te2-incorporated Bi0.5Sb1.5Te3 thermoelectric alloys(Elsevier, 2024) Park, Hyunjin; Kim, Sang-il; Hwang, Seong-Mee; Kim, Se Yun; Lee, Kyu Hyoung; Kim, Hyun-Sik; Department of Chemistry; Yahyaoğlu, Müjde; Sağlık, Kıvanç; Öztulum, Sefa; 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); Graduate School of Sciences and Engineering; College of SciencesWhile extensive research has explored Cu doping in n-type Bi-2(Te,Se)(3) for its beneficial effects on reproducibility and mobility, its impact on p-type (Bi,Sb)(2)Te-3 remains incompletely understood. Recently, Saglik et al. demonstrated Cu2.9Te2 incorporation into Bi0.5Sb1.5Te3 as a novel approach for simultaneous Cu doping and intercalation, surpassing prior studies focused solely on Cu doping at Bi/Sb sites. The influence of additional Cu intercalation on both electronic band parameters (density-of-states effective mass, deformation potential, and weighted mobility) and phonon scattering by point defects has yet to be investigated. Here, we employ the Effective Mass model to comparatively assess the impact of Cu intercalation on these band parameters relative to single Cu doping. Furthermore, the Callaway-von Baeyer and Debye-Callaway models are employed to evaluate the effect of Cu intercalation in scattering phonons. Our findings reveal that additional Cu intercalation effectively suppresses the lattice thermal conductivity of Bi0.5Sb1.5Te3 to the amorphous limit, offering the potential to improve the figure-of-merit (zT) to similar to 2.0 near 420 K with optimized carrier concentration. This approach highlights Cu intercalation as a readily applicable and powerful tool for maximizing the thermoelectric performance of Bi2Te3-based materials.Publication Metadata only Enhanced performance and cycling behavior in symmetric supercapacitors developed by pure HfB2 and HfB2-SiC composites(Elsevier, 2024) Yildirim, Ipek Deniz; Gungor, Ahmet; Erdem, Emre; Department of Chemistry; Paksoy, Aybike; Arabi, Seyedehnegar; Balcı, Özge; 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); Graduate School of Sciences and Engineering; College of SciencesBoron-based materials have attracted growing interest as promising candidates for energy storage applications. This study focuses on synthesizing pure HfB2 powders through a straightforward method involving the mechanical activation of a powder mixture comprising hafnium tetrachloride (HfCl4), boron (B), and magnesium (Mg). The HfB2 powders were mechanically alloyed with varying amounts of SiC powders to create HfB2-based composite structures. The chemical and microstructural properties of the synthesized samples were assessed using XRD, SEM/EDX, and DLS characterization techniques. Supercapacitor device performances of all resulting powders as symmetrical electrodes were systematically investigated. The test results revealed that the pure HfB2 electrode material exhibited a pseudocapacitor behavior, whereas composite powders exhibited battery-like behavior. Composite powders, demonstrated enhanced supercapacitor performance surpassing that of pure powder in terms of energy density and cycle efficiency. The pure HfB2 electrode displayed the highest power density (95 Wkg 1) among all samples: Its distinctive pseudocapacitor behavior results in the highest power density, providing valuable insights into the intricate relationship between composition and electrochemical performance in boron-based supercapacitor materials. Moreover, these results propose that by synthesizing composite powders, the charge storage mechanism can be altered and used to improve the energy density.Publication Metadata only Surface hardening of Ti-AL-V superalloy spinal implant by using the boronization method(IOS Press, 2024) Hekimoğlu, Mehdi; Özer, Hidir; Onursal, Ceylan; Department of Chemistry; Kiraz, Kamil; Özer, Ali Fahir; Department of Chemistry; College of Sciences; School of MedicineBackground: We compared the raw Ti-Al-V super alloy transpedicular implant screws with boronized and surfacehardened transpedicular implant screws. OBJECTIVE: To improve patients' postoperative prognosis with the production of harder and less fragile screws. METHODS: Surface hardening was achieved by applying green-body encapsulation of the specimen with elemental boron paste which is sintered at elevated temperatures to ensure the boron-metal diffusion. Boron transported into the Ti-Al-V super alloy matrix gradually while suppressing aluminum and a homogeneously boronized surface with a thickness of similar to 15 microns was obtained. The uniform external shell was enriched with TiB2, which is one of the hardest ceramics. The Ti-Al-V core material, where boron penetration diminishes, shows cohesive transition and ensures intact core-surface structure. RESULTS: Scanning electron microscope images confirmed a complete homogeneous, uniform and non-laminating surface formation. Energy-dispersive X-ray monitored the elemental structural mapping and proved the replacement of the aluminum sites on the surface with boron ending up the TiB2. The procedure was 8.6 fold improved the hardness and the mechanical resistance of the tools. CONCLUSIONS: Surface-hardened, boronized pedicular screws can positively affect the prognosis. In vivo studies are needed to prove the safety of use.Publication Metadata only Feeble single-atom Pd catalysts for H2 production from formic acid(American Chemical Society, 2024) Nao Tsunoji; Shinya Mine; Takashi Toyao; Ken-ichi Shimizu; Tetsuro Morooka; Takuya Masuda; M. Hussein N. Assadi; Yusuke Ide; Department of Chemistry; Doustkhah, Esmail; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of SciencesSingle-atom catalysts are thought to be the pinnacle of catalysis. However, for many reactions, their suitability has yet to be unequivocally proven. Here, we demonstrate why single Pd atoms (Pd-SA) are not catalytically ideal for generating H-2 from formic acid as a H-2 carrier. We loaded Pd-SA on three silica substrates, mesoporous silicas functionalized with thiol, amine, and dithiocarbamate functional groups. The Pd catalytic activity on amino-functionalized silica (SiO2-NH2/Pd-SA) was far higher than that of the thiol-based catalysts (SiO2-S-Pd-SA and SiO2-NHCS2-Pd-SA), while the single-atom stability of SiO2-NH2/Pd-SA against aggregation after the first catalytic cycle was the weakest. In this case, Pd aggregation boosted the reaction yield. Our experiments and calculations demonstrate that Pd-SA in SiO2-NH2/Pd-SA loosely binds with amine groups. This leads to a limited charge transfer from Pd to the amine groups and causes high aggregability and catalytic activity. According to the density functional calculations, the loose binding between Pd and N causes most of Pd's 4d electrons in amino-functionalized SiO2 to remain close to the Fermi level and labile for catalysis. However, Pd-SA chemically binds to the thiol group, resulting in strong hybridization between Pd and S, pulling Pd's 4d states deeper into the conduction band and away from the Fermi level. Consequently, fewer 4d electrons were available for catalysis.