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Item Metadata only Enhancing thermoelectric and mechanical properties of P-Type (Bi, Sb)2Te3 through rickardite mineral (Cu2.9Te2) incorporation(Amer Chemical Soc, 2023) 0000-0003-1164-1973; 0000-0001-9098-2869; N/A; Department of Chemistry; N/A; N/A; Aydemir, Umut; Yahyaoğlu, Müjde; Sağlık, Kıvanç; Faculty Member; PhD Student; PhD Student; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 58403; N/A; N/ABi2Te3-based alloys are widely utilized in Peltier coolers owing to their highest thermoelectric performance at near-room-temperatures. However, their peak dimensionless thermo-electric figure of merit, zT, is limited to a narrow temperature window due to minority carrier excitation emerging upon heating at around 400 K. Here, we show how this issue can be overcome by incorporating a synthetic rickardite mineral, Cu3-xTe2, in p-type (Bi, Sb)2Te3. The significant enhancement of the electronic and thermal properties could be achieved due to small Cu incorporation into the crystal structure of (Bi, Sb)2Te3 and homogeneous precipitation of Cu3-xTe2 at the grain boundaries. This leads to a high average zT value (zTave) of 1.22 between 350 and 500 K for two compositions, Bi0.5Sb1.5Te3 (BST-5) and Bi0.3Sb1.7Te3 (BST-3), with peak zT values of 1.32 at 467 K and 1.30 at 400 K, respectively. These high zT values result in a considerably high maximum device ZT of ca. 1.15 and a theoretical efficiency of up to 7% between 325 and 525 K. Additionally, room-temperature micro-hardness is substantially improved, which is desirable for constructing reliable and durable thermoelectric modules.Item Metadata only In situ design of a nanostructured ınterface between NiMo and CuO derived from metal-organic framework for enhanced hydrogen evolution in alkaline solutions(Amer Chemical Soc, 2024) 0000-0003-1164-1973; 0000-0002-2991-5488; N/A; 0000-0003-0832-0546; Yildirim, Ipek Deniz; Erdem, Emre; Department of Chemistry; N/A; N/A; N/A; Aydemir, Umut; Peighambardoust, Naeimeh Sadat; Chamani, Sanaz; Sadeghi, Ebrahim; Faculty Member; Researcher; Researcher; PhD Student; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; N/A; N/A; Graduate School of Sciences and Engineering; 58403; N/A; N/A; N/AHydrogen shows great promise as a carbon-neutral energy carrier that can significantly mitigate global energy challenges, offering a sustainable solution. Exploring catalysts that are highly efficient, cost-effective, and stable for the hydrogen evolution reaction (HER) holds crucial importance. For this, metal-organic framework (MOF) materials have demonstrated extensive applicability as either a heterogeneous catalyst or catalyst precursor. Herein, a nanostructured interface between NiMo/CuO@C derived from Cu-MOF was designed and developed on nickel foam (NF) as a competent HER electrocatalyst in alkaline media. The catalyst exhibited a low overpotential of 85 mV at 10 mA cm(-2) that rivals that of Pt/C (83 mV @ 10 mA cm(-2)). Moreover, the catalyst's durability was measured through chronopotentiometry at a constant current density of -30, -100, and -200 mA cm(-2) for 50 h each in 1.0 M KOH. Such enhanced electrocatalytic performance could be ascribed to the presence of highly conductive C and Cu species, the facilitated electron transfer between the components because of the nanostructured interface, and abundant active sites as a result of multiple oxidation states. The existence of an ionized oxygen vacancy (O-v) signal was confirmed in all heat-treated samples through electron paramagnetic resonance (EPR) analysis. This revelation sheds light on the entrapment of electrons in various environments, primarily associated with the underlying defect structures, particularly vacancies. These trapped electrons play a crucial role in augmenting electron conductivity, thereby contributing to an elevated HER performance.Item Metadata only Designing ın situ grown ternary oxide/2D Ni-BDC MOF nanocomposites on nickel foam as efficient electrocatalysts for electrochemical water splitting(Amer Chemical Soc, 2022) 0000-0003-1164-1973; 0000-0002-2991-5488; N/A; 0000-0003-0832-0546; Department of Chemistry; N/A; N/A; N/A; Aydemir, Umut; Peighambardoust, Naeimeh Sadat; Chamani, Sanaz; Sadeghi, Ebrahim; Faculty Member; Researcher; Researcher; PhD Student; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; N/A; N/A; Graduate School of Sciences and Engineering; 58403; N/A; N/A; N/AThe security of future energy, hydrogen, is subject to designing high-performance, stable, and low-cost electrocatalysts for hydrogen and oxygen evolution reactions (HERs and OERs), for the realization of efficient overall water splitting. Two-dimensional (2D) metal-organic frameworks (MOFs) introduce a large family of materials with versatile chemical and structural features for a variety of applications, such as supercapacitors, gas storage, and water splitting. Herein, a series of nanocomposites based on NCM/Ni-BDC@NF (N = Ni, C = Co, M:F = Fe, C = Cu, and Z = Zn, BDC: benzene dicarboxylic acid, NF: nickel foam) were directly developed on NF using a facile yet scalable solvothermal method. After coupling, the electronic structure of metallic atoms was well-modulated. Based on the XPS results, for the NCF/Ni-BDC, cationic atoms shifted to higher oxidation states, favorable for the OER. Conversely, for the NCZ/Ni-BDC and NCC/Ni-BDC nanocomposites, cationic atoms shifted to lower oxidation states, advantageous for the HER. The as-prepared NCF/ Ni-BDC demonstrated prominent OER performance, requiring only 1.35 and 1.68 V versus a reversible hydrogen electrode to afford 10 and 50 mA cm(-2) current densities, respectively. On the cathodic side, NCZ/Ni-BDC exhibited the best HER activity with an overpotential of 170 and 350 mV to generate 10 and 50 mA cm(-2), respectively, under 1.0 M KOH medium. In a two-electrode alkaline electrolyzer, the assembled NCZ/Ni-BDC (cathode). NCF/Ni-BDC (anode) couple demanded a cell voltage of only 1.58 V to produce 10 mA cm(-2). The stability of NCF/Ni-BDC toward OER was also exemplary, experiencing a continuous operation at 10, 20, and 50 mA cm(-2) for nearly 45 h. Surprisingly, the overpotential after OER stability at 50 mA cm(-2) dropped drastically from 450 to 200 mV. Finally, the faradaic efficiencies for the overall water splitting revealed the respective values of 100 and 85% for the H-2 and O-2 production at a constant current density of 20 mA cm(-2).Item Metadata only Tetra-functional multilayer coatings for cardiovascular stent materials(Elsevier, 2023) 0000-0001-6624-3505; 0000-0002-6976-942X; 0000-0001-6753-9316; 0000-0001-5547-6653; 0000-0002-7698-0872; N/A; 0000-0002-4588-5231; 0000-0003-0984-0375; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; N/A; N/A; N/A; Department of Molecular Biology and Genetics; N/A; N/A; N/A; Kavaklı, İbrahim Halil; Güner, Pınar Tatar; Motallebzadeh, Amir; Yalçın, Özlem; Gürpınar, Yunus; Sürme, Saliha; Ijaz, Aatif; Saadatlou, Ghazaleh Azizi; Sipahioğlu, Dilara; Faculty Member; Teaching Faculty; Researcher; Faculty Member; Researcher; Teaching Faculty; Researcher; PhD Student; Master Student; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; College of Sciences; N/A; School of Medicine; N/A; College of Sciences; N/A; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 40319; 188227; N/A; 218440; N/A; 389349; N/A; N/A; N/AFunctional coatings have been of great interest in enhancing the performance of implants in recent years. Here, for the first time, preparation and characterization of a tetra-functional coating is reported, exhibiting anticorrosion, antibacterial, biocompatible, and anticoagulant behaviors. Poly(2-ethyl-2-oxazoline)-copolyethyleneimine (PEOX-co-PEI) stabilized silver nanoparticles (AgNPs) and heparin were used to prepare the multifunctional multilayers. The coatings were deposited on nitinol and 316 L stainless steel substrates, the most used materials in coronary stents, via layer-by-layer (LbL) technique. Corrosion current density values obtained from Tafel plots are 1.61 x 10-9 A/cm2 and 6.79 x 10-8A/cm2 for coated and uncoated 316 L substrate, respectively. Similarly, the corrosion current density values shifted from 1.00 x 10-8A/cm2 for uncoated nitinol to 4.77 x 10-10A/cm2 after coating. Contact killing method against gram-positive (Staphylococcus aureus) and gram-negative (Pseudomonas aeruginosa) bacterial species concluded that the presence of the coating on the surfaces of the materials reduces the number of the survived colonies (in CFU/mL) for more than 99.9%independent of the underlying metal within 3 hours of incubation time. Prepared coatings demonstrated above 90% relative viability compared to the positive control in MTT assay using human umbilical vein endothelial cells (HUVEC), indicating no cytotoxic effect on adjacent healthy cells. The coagulation assay also exhibited a 50% reduction in the coagulation rate after coating compared to the bare substrates, confirming the antithrombogenicity of the coatings.Item Metadata only Tunable photocatalytic activity of CoFe prussian blue analogue modified SrTiO3 core-shell structures for solar-driven water oxidation(American Chemical Society, 2023) 0000-0003-1164-1973; 0000-0002-2991-5488; Sadigh Akbari, Sina; Lomlu, Rana; Karadas, Ferdi; Department of Chemistry; N/A; Aydemir, Umut; Peighambardoust, Naeimeh Sadat; Faculty Member; Researcher; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; N/A; 58403; N/AThis study presents a pioneering semiconductor-catalyst core-shell architecture designed to enhance photocatalytic water oxidation activity significantly. This innovative assembly involves the in situ deposition of CoFe Prussian blue analogue (PBA) particles onto SrTiO3 (STO) and blue SrTiO3 (bSTO) nanocubes, effectively establishing a robust p-n junction, as demonstrated by Mott-Schottky analysis. Of notable significance, the STO/PB core-shell catalyst displayed remarkable photocatalytic performance, achieving an oxygen evolution rate of 129.6 μmol g-1 h-1, with stability over an extended 9-h in the presence of S2O82- as an electron scavenger. Thorough characterization unequivocally verified the precise alignment of the band energies within the STO/PB core-shell assembly. Our research underscores the critical role of tailored semiconductor-catalyst interfaces in advancing the realm of photocatalysis and its broader applications in renewable energy technologies. © 2023 The Authors. Published by American Chemical Society.Item Metadata only Synthesis and capacitive performance of ZrB2 and its composites as supercapacitor electrodes(Elsevier, 2023) 0000-0001-6756-3180; 0000-0003-1925-9453; N/A; Buldu-Akturk, Merve; Erdem, Emre; Department of Chemistry; N/A; N/A; Balcı, Özge Çağıran; Paksoy, Aybike; Arabi, Seyedehnegar; Researcher; Master Student; PhD Student; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 295531; N/A; N/AThe possibility of using zirconium diboride (ZrB2) as an electrode for supercapacitor devices has yet to be extensively studied, even though there is a wealth of literature on various properties of ZrB2. In this study, ZrB2 and its composites were directly assembled as electrode materials into symmetric and asymmetric supercapacitor devices. ZrB2 powders were synthesized by using mechanical activation assisted direct synthesis route followed by a purification step. Powders were illustrated with precise size tuning in the 200-500 nm range. Then, the ZrB2-based composite materials containing silicon carbide (SiC) particles were prepared by using a mechanical alloying process. Microstructural and thermal analyses of the particles were carried out and optimum powders were selected for the measurements of electrochemical performance. Both symmetric and asymmetric supercapacitors exhibited excellent cycling performances: After 50 cycles, the devices display 79 and 69% capacitance retention as well as 108 and 123% coulombic efficiency at 0.1 A g-1, respectively for the symmetric ZrB2/ZrB2 and asymmetric ZrB2/ZrB2-15 wt%SiC supercapacitors. The symmetric supercapacitor exhibited higher performance than asymmetric one with a specific energy and power density of 4.2 W h kg-1 and 150 W kg-1, respectively. As a result, high energy density and high capacity values, and excellent cycling performances are obtained, meaning that ZrB2 and its composites are promising materials for energy storage purposes.Item Metadata only Understanding the enhanced corrosion performance of two novel Ti- based biomedical high entropy alloys(Elsevier Science Sa, 2023) 0000-0001-9961-7702; 0000-0001-6763-5770; 0000-0001-8160-0478; 0000-0002-8430-6941; 0000-0002-9841-7028; 0000-0003-4718-1243; Unal, U.; Maier, H. J.Yilmaz, R.; Department of Mechanical Engineering; N/A; N/A; N/A; N/A; Department of Chemistry; Canadinç, Demircan; Özdemir, Hüseyin Can; Kılıç, Elif Bedir; Nazarahari, Alireza; Yılmaz, Bengisu; Ünal, Uğur; Faculty Member; PhD Student; PhD Student; PhD Student; PhD Student; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of 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 Sciences; 23433; N/A; N/A; N/A; N/A; 42079The microstructure and corrosion behavior of two novel biomedical high entropy alloys (HEA)s, namely Hf27Nb12Ta10Ti23Zr28 and Hf30Nb14Ta10Ti28Zr18 that were previously designed utilizing machine learning, were investigated in depth. The microstructure of the alloys was determined to be dendritic, with some elemental segregations governed by the solidification kinetics occurring during the arc-melting process. Static immersion experiments were carried out in artificial saliva (AS) and simulated body fluid (SBF) to investigate the ion release behavior of the HEAs and reveal the dissolution kinetics of the passive film forming on the surface. The composition of the corresponding surface oxide layers was examined using X-ray photoelectron spectroscopy, which provided detailed insight into the stability of passive oxide layers and sub-oxide formation. Potentiodynamic polarization experiments performed in AS and SBF at 37 oC demonstrated that both HEAs exhibit superior corrosion behavior as compared to the CoCrMo alloy, one of the conventional metallic implant materials of choice. (c) 2023 Elsevier B.V. All rights reserved.Item Metadata only Aqueous colloidal nanoplatelets for imaging and improved ALA-based photodynamic therapy of prostate cancer cells(Royal Soc Chemistry, 2023) 0000-0001-5601-8814; 0000-0003-4952-7981; 0000-0001-6573-8565; Onbasli, Kubra; Demirci, Gozde; Isik, Furkan; Durmusoglu, Emek Goksu; Demir, Hilmi Volkan; Acar, Havva Yagci; Department of Chemistry; N/A; N/A; Acar, Havva Funda Yağcı; Demirci, Gözde; Onbaşlı, Kübra; Faculty Member; Master Student; PhD Student; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 178902; N/A; 365341Fluorescent, CdSe/CdS core/crown heterostructured nanoplatelets (NPLs) were transferred to the water via a simple, single-step ligand exchange using 2-mercaptopropionic acid in a simple extraction process. These stable, aqueous NPLs were loaded with a modal drug, 5-aminolevulinic acid (ALA). ALA-loaded NPLs emerged as a new class of theranostic nanoparticles for image-guided enhanced photodynamic therapy of both androgen-dependent and -independent human prostate cancer cells.Item Metadata only Ti3C2MXene/polyaniline/montmorillonite nanostructures toward solvent-free powder coatings with enhanced corrosion resistance and mechanical properties(Amer Chemical Soc, 2023) 0000-0003-1164-1973; 0000-0003-3243-6442; Hosseini, Seyyedeh Fatemeh; Dorraji, Mir Saeed Seyed; Rasoulifard, Mohammad Hossein; Department of Chemistry; N/A; Aydemir, Umut; Nazarlou, Ziba; Faculty Member; PhD Student; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); College of Sciences; Graduate School of Sciences and Engineering; 58403; N/ASolvent-free powdercoatings have become very popular in the coatingindustry in replacing conventional liquid coatings for the last decades.However, poor adhesion of powder coatings to the substrate and microporesinevitably created during the curing process of coatings lead to localizedcorrosion and reduced mechanical resistance. For this purpose, Ti3C2 MXene/polyaniline (PANI)/montmorillonite (MMT)nanocomposites with superior conductivity and adhesion capabilitieswere incorporated into the eco-friendly powder coating. The as-synthesizednanocomposites were analyzed using various techniques such as Fouriertransform infrared spectroscopy, X-ray diffraction, X-ray photoelectronspectroscopy, high-resolution transmission electron microscopy, field-emissionscanning electron microscopy, and Raman spectroscopy. To evaluatethe effectiveness of the powder coating in preventing corrosion ona mild steel substrate, two methods were employed: potentiodynamicpolarization and electrochemical impedance spectroscopy. The electrochemicaltests revealed that an excellent dispersion of 1.5 wt % Ti3C2 MXene/PANI/MMT nanosheets in a polyester/epoxy powdercoating resulted in superior anti-corrosion performance (4.8 x10(6) omega) after 42 days of immersion in 3.5 wt % NaClas compared to blank samples (7.2 x 10(2) omega).According to Tafel analysis, the corrosion potential of the optimalsample is -0.062 V, which is more positive than that of thepristine powder coating (-0.83 V). The polarization resistance(R (p)) and corrosion current (i (corr)) of the optimal sample are determined to be 3.39x 10(6) omega center dot cm(2) and 7.69 x10(-9) A center dot cm(-2), respectively.Moreover, the optimal sample marginally increased the hardness (229.42MPa) compared to the pure sample (152.68 MPa) due to the synergisticeffect of Ti3C2 MXene and flake-like MMT nanoparticles,which results in an improvement in the mechanical strength of powdercoatings. Additionally, the presence of PANI caused further crosslinkingand modulation of the electrical conductivity of the produced nanocomposites.The present study proposes a practical method to enhance the mechanicaland shielding properties of solvent-free powder coatings, making themsuitable for use in various real-world applications, including commercial,medical, and household sectors.Item Metadata only A facile tert-butyl nitrite-assisted preparation of deamino graphitic carbon nitride (DA-gCN) as a photocatalyst for the C-H arylation of heteroarenes using anilines as radical source(Tubitak Scientific and Technological Research Council Turkey, 2023) 0000-0003-1622-4992; N/A; 0000-0002-6922-3187; Department of Chemistry; N/A; N/A; Metin, Önder; Palani, Natarajan; Karapınar, Begümhan; Faculty Member; Researcher; PhD Student; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; N/A; Graduate School of Sciences and Engineering; 46962; N/A; N/AIn pristine graphitic carbon nitride (g-CN), amino groups often function as structural defects that trap photogenerated charges, resulting in low photocatalytic activity as well as reaction with nitrite, aldehyde, etc., ensuing in poor product yield. Without significantly altering the optical characteristics, the removal of amino groups is necessary to increase the photocatalytic activity and structural stability of pristine g-CN. The deamino graphitic carbon nitride (DA-gCN-5) was prepared by tert-butyl nitrite (TBN)treatment, characterized and used as a photocatalyst for the radical C-H arylation of heteroarenes using anilines as radical source. Indeed, the photophysical characteristics of DA-gCN-5 and those of pristine g-CN are very comparable, except that DA-gCN-5 has a fewer residual amino groups, higher crystallinity, and compressed structure with a different morphology. Moreover, DA-gCN-5- catalyzed C-H arylation reaction offers greater product yield in a shorter reaction time compared to that of pristine g-CN in the coupling between heteroarenes and the in situ generated aryl diazonium salts from anilines under visible light irradiation. The amino groups in pristine g-CN absorbed the TBN that was added to convert aniline into the appropriate diazonium ions during the reaction. As a result, deamino graphitic carbon nitride produced by chemical treatment has better photophysical properties and catalytic activity than pristine g-CN. Additionally, this is the first method that uses diazotization reaction for the preparation of deamino graphitic carbon nitride, as far as we are aware.