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Publication Metadata only Al-Sm alloys under far-from-equilibrium conditions(Springer International Publishing AG, 2021) Okuyucu, Can; Kaygusuz, Burçin; Işıksaçan, Cemil; Meydanoğlu, Onur; Özerinç, Sezer; Kalay, Yunus Eren; N/A; Motallebzadeh, Amir; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/ATraditional Al alloys have shown tremendous potential in the aerospace industry due to their attractive properties such as ductility, fracture toughness, and fatigue resistance. However, modern aerospace applications call for next-generation Al alloys with a stringent combination of properties such as high strength, low density, and excellent environmental stability. In that sense, we studied highly driven Al-Rare-Earth (RE) alloys under far-from-equilibrium conditions to investigate the possible effects of cooling rate on the expected microstructure, thus mechanical properties. Al94Sm6 was produced using a copper wheel melt spinner. XRD analysis showed the Sm is entirely trapped within the Al matrix. The heat-treated specimens resulted in the formation of the nanocrystalline Al4Sm phase embedded in the Al matrix, with a two-step precipitation sequence. The hardness values determined by nanoindentation shows that the initial supersaturated solid solution has 3.83 GPa hardness, while the heat-treated ones have 3.34 GPa. The mechanisms behind this extreme strength and ductility through solute trapping, and subsequent heat-treatments were discussed in detail using a combined study of micromechanical characterization, nanoindentation , electron microscopy, XRD, and DSC.Publication Metadata only Ammonia decomposition on a highly-dispersed carbon-embedded iron catalyst derived from Fe-BTC: stable and high performance at relatively low temperatures(Elsevier, 2020) N/A; N/A; Department of Chemical and Biological Engineering; Akarçay, Özge; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; PhD Student; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 384798; 59917Fe-BTC (iron 1,3,5-benzenetricarboxylic acid), a commercially available metal organic framework (MOF), was used as a sacrificial template to produce a series of carbon-embedded Fe catalysts upon its pyrolysis at different temperatures. The catalyst prepared by pyrolyzing Fe-BTC at 400 degrees C under flowing N-2 provided a high graphitic degree on the carbon support hosting highly dispersed Fe species at a Fe loading of 34 wt%. Performance measurements on ammonia decomposition to produce COx-free hydrogen showed that this catalyst provided an ammonia conversion of 73.8% at a space velocity of 6000 cm(3) NH3 h(-1) g(cat)(-1) and at 500 degrees C for at least 120 h. This stable performance, exceeding that of some of the best non-noble metal catalysts, was associated with the presence of highly-dispersed Fe species at a significantly high Fe loading, embedded in a carbonaceous shell. The presence of the carbonaceous shell not only protected the active species against sintering, but also made them electron rich owing to its high level of graphitization.Publication Metadata only An ultra-compact and wireless tag for battery-free sweat glucose monitoring(Elsevier Advanced Technology, 2022) N/A; Department of Mechanical Engineering; N/A; N/A; Department of Mechanical Engineering; N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Mirzajani, Hadi; Abbasiasl, Taher; Mirlou, Fariborz; İstif, Emin; Bathaei, Mohammad Javad; Dağ, Çağdaş; Deyneli, Oğuzhan; Dereli, Dilek Yazıcı; Beker, Levent; Researcher; PhD Student; PhD Student; Other; PhD Student; Faculty Member; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Koç Üniversitesi İş Bankası Enfeksiyon Hastalıkları Uygulama ve Araştırma Merkezi (EHAM) / Koç University İşbank Center for Infectious Diseases (KU-IS CID); n2STAR-Koç University Nanofabrication and Nanocharacterization Center for Scientifc and Technological Advanced Research; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; N/A; School of Medicine; School of Medicine; College of Engineering; N/A; N/A; N/A; N/A; N/A; N/A; 171914; 179659; 308798Glucose monitoring before, during, and after exercise is essential for people with diabetes as exercise increases the risk of activity-induced hyper- and hypo-glycemic events. The situation is even more challenging for athletes with diabetes as they have impaired metabolic control compared to sedentary individuals. In this regard, a compact and noninvasive wearable glucose monitoring device that can be easily worn is critical to enabling glucose monitoring. This report presents an ultra-compact glucose tag with a footprint and weight of 1.2 cm(2) and 0.13 g, respectively, for sweat analysis. The device comprises a near field communication (NFC) chip, antenna, electrochemical sensor, and microfluidic channels implemented in different material layers. The device has a flexible and conformal structure and can be easily attached to different body parts. The battery-less operation of the device was enabled by NFC-based wireless power transmission and the compact antenna. Femtosecond laser ablation was employed to fabricate a highly compact and flexible NFC antenna. The proposed device demonstrated excellent operating characteristics with a limit of detection (LOD), limit of quantification (LOQ), and sensitivity of 24 mu M, 74 mu M, and 1.27 mu A cm(-2) mM(-1), respectively. The response of the proposed sensor in sweat glucose detection and quantification was validated by nuclear magnetic resonance spectroscopy (NMR). Also, the device's capability in attachment to the body, sweat collection, and glucose measurement was demonstrated through in vitro and in vivo experiments, and satisfactory results were obtained.Publication Metadata only Binary CuPt alloy nanoparticles assembled on reduced graphene oxide-carbon black hybrid as efficient and cost-effective electrocatalyst for PEMFC(Pergamon-Elsevier Science Ltd, 2019) Yılmaz, Melike Sevim; Kaplan, Begüm Yarar; Gürsel, Selmiye Alkan; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; College of Sciences; 46962Addressed herein is the synthesis of binary CuPt alloy nanoparticles (NPs), their assembly on reduced graphene oxide (rGO), Vulcan XC72 (VC) and their hybrid (rGO-VC) to be utilized as electrocatalysts for fuel cell reactions (HOR and ORR) in acidic medium and PEMFC tests. The synthesis of nearly-monodisperse Cu45Pt55 alloy NPs was achieved by using a chemical reduction route comprising the reduction of commercially available metal precursors in a hot surfactant solution. As-synthesized Cu45Pt55 alloy NPs were then assembled on three support materials, namely rGO, VC and rGO-VC) via liquid phase self-assembly method. After the characterization, the electrocatalysts were prepared by mixing the yielded materials with Nafion and their electrocatalysis performance was investigated by studying CV and LSV for HOR and ORR in acidic medium. Among the three electrocatalysts tested, Cu45Pt55/rGO-VC hybrid showed the highest catalytic activity with ECSA of 119 m(2) g(-1) and mass activity of 165 mA mg(pt)(-1). After the evaluation of electrochemical performance of the three prepared electrocatalysts, their performance was then evaluated in fuel cell conditions. In similar to electrochemical activities, the Cu45Pt55/rGO-VC hybrid electrocatalyst showed a superior fuel cell performance and power output by providing a maximum power of 480 mW cm(-2) with a relatively low Pt loading (0.28 mg cm(-2)). Additionally, the Cu45Pt55/rGO-VC hybrid electrocatalyst exhibited substantially better activity as compared to Pt/rGO-VC electrocatalyst. Therefore, the present study confirmed that alloying Pt with Cu enhances the catalytic activity of Pt metal along with the help of beneficial features of rGO-VC hybrid support material. It should be noted that this is the first example of studying PEMFC performance of CuPt alloy NPs supported on rGO, VC and rGO-VC hybrid.Publication Metadata only Binary CuPt alloy nanoparticles assembled on reduced graphene oxide-carbon black hybrid as efficient and cost-effective electrocatalyst for PEMFC [Int J Hydrogen Energy 44 (2019) 14184–14192](Pergamon-Elsevier Science Ltd, 2021) Sevim, Melike; Kaplan, Begüm Yarar; Gürsel, Selmiye Alkan; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; College of Sciences; 46962N/APublication Metadata only Boosting electrocatalysis of oxygen reduction and evolution reactions with cost-effective cobalt and nitrogen-doped carbons prepared by simple carbonization of ionic liquids(Pergamon-Elsevier Science Ltd, 2022) Zdolsek, Nikola; Vujkovic, Milica; Brkovic, Snezana; Jocic, Ana; Dimitrijevic, Aleksandra; Trtic-Petrovic, Tatjana; Sljukic, Biljana; Department of Chemistry; Metin, Önder; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; 46962Development of cost-effective, bi-functional carbon electrocatalysts via direct carbonization of ionic liquids (bis(cholinium) tetrachlorocobaltate(II) ([Ch](2)[CoCl4]) and bis(1-butyl-3methylimidazolium) tetrachlorocobaltate(II) ([Bmim](2)[CoCl4])) is reported herein for the first time. Carbon electrocatalysts, dual-doped with cobalt and nitrogen, were tested for oxygen reduction (ORR) and oxygen evolution (OER) reactions. Both materials show high bifunctional catalytic activity and excellent stability due to synergistic effects arising from the presence of nitrogen and cobalt. Electrocatalyst prepared by carbonization of [Ch](2)[-CoCl4] show exceptional activity and selectivity toward ORR. Conversely, electrocatalyst prepared from [Bmim](2)[CoCl4] showed a slightly better OER performance indicating that different catalytic sites are responsible for O-2 reduction and H2O oxidation. Parent CoO particles with graphitic nitrogen boost activity for ORR, while elemental Co supported by nitrogen atoms is responsible for OER activity. Finally, energy consumption during electrolytic oxygen production was calculated revealing energy saving when using two materials as anode electrocatalysts.Publication Metadata only Charge storage characteristics of layer-by-layer assembled nickel hydroxide and graphene oxide nanosheets(Springer, 2019) N/A; Department of Chemistry; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Ünal, Uğur; Researcher; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; N/A; 42079In this study, layer-by-layer assembled thin films composed of nickel hydroxide and graphene oxide nanosheets were produced via simple dip coating process. The surface topography of the thin films was investigated by atomic force microscopy measurements. Electrical conductivity of the thin films was enhanced by chemical reduction with hydrazine vapor. The effect of chemical reduction on the surface chemical structure was analyzed by X-ray photoelectron spectroscopy. To utilize the produced thin films as possible electrodes for electrochemical energy storage devices, cyclic voltammetric measurements were performed. The areal capacitance of a reduced 9-bilayer [Ni(OH)(2)/graphene oxide] thin film reached 5.2mFcm(-2) at a scan rate of 2mVs(-1), outperforming similar layer-by-layer assembled metal hydroxide/graphene thin films. Lastly, charge storage characteristics of as-deposited and reduced films were investigated by performing cyclic voltammetry at different scan rates and electrochemical impedance spectroscopy.Publication Metadata only COx-free hydrogen production from ammonia decomposition over sepiolite-supported nickel catalysts(Pergamon-Elsevier Science Ltd, 2018) Soyer-Uzun, Sezen; N/A; N/A; N/A; N/A; Department of Chemical and Biological Engineering; Öztulum, Samira Fatma Kurtoğlu; Sarp, Seda; Akkaya, Ceren Yılmaz; Yağcı, Mustafa Barış; Uzun, Alper; PhD Student; Undergraduate Student; Researcher; Researcher; 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; College of Engineering; College of Engineering; N/A; College of Engineering; 384798; N/A; N/A; N/A; 59917Sepiolite, a clay mineral, was utilized as a support for nickel-based catalysts for COx-free hydrogen production from ammonia decomposition. First, the physical and chemical properties of sepiolite were changed by calcining it at temperatures varying from 500 to 1000 degrees C, then nickel was impregnated on these calcined supports and tested for ammonia decomposition at various temperatures following reduction at 650 degrees C. Results indicated that even though the catalysts contained almost the same amount of nickel, they showed different hydrogen production performance. Detailed characterization of the catalysts before and after reaction illustrated that the support obtained by calcining sepiolite at 700 degrees C shows good basic properties with a high surface area offering a high degree of nickel dispersion. These properties lead to promising hydrogen production rates which are on par, if not higher, than most of the nickel-based catalysts prepared on supports, which are either not cheap or require tedious preparation procedures.Publication Metadata only Detection of human kappa-opioid antibody using microresonators with integrated optical readout(Elsevier advanced Technology, 2010) N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Department of Mechanical Engineering; Timurdoğan, Erman; Özber, Natali; Nargül, Sezin; Yavuz, Serhat; Kılıç, M. Salih; Kavaklı, İbrahim Halil; Ürey, Hakan; Alaca, Burhanettin Erdem; PhD Student; Master Student; PhD Student; Master Student; Resercher; Faculty Member; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Department of Mechanical 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 Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 40319; 8579; 115108Label-free detection of the interaction between hexahistidine-tagged human kappa-opioid receptor membrane protein and anti-His antibody is demonstrated in liquid by an optical microelectromechanical system utilizing electromagnetically actuated microresonators Shift in resonance frequency due to accretion of mass on the sensitive surface of microresonators is monitored via an integrated optical readout a frequency resolution of 2 Hz is obtained Together with a sensitivity of 7 ppm/(ng/ml)) this leads to a minimum detectable antibody concentration of 57 ng/ml for a 50-kHz device the measurement principle is shown to impart immunity to environmental noise, facilitate operation in liquid media and bring about the prospect for further miniaturization of actuator and readout leading to a portable biochemical sensor.Publication Metadata only Digital monitoring of the microchannel filling flow dynamics using a non-contactless smartphone-based nano-liter precision flow velocity meter(Elsevier Advanced Technology, 2024) Xu, Weiming; Köydemir, Hatice Ceylan; Department of Mechanical Engineering; Atik, Abdulkadir Yasin; Beker, Levent; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of EngineeringMicrofluidic systems find widespread applications in diagnostics, biological research, chemistry, and engineering studies. Among their many critical parameters, flow rate plays a pivotal role in maintaining the functionality of microfluidic systems, including droplet-based microfluidic devices and those used in cell culture. It also significantly influences microfluidic mixing processes. Although various flow rate measurement devices have been developed, the challenge remains in accurately measuring flow rates within customized channels. This paper presents the development of a 3D-printed smartphone-based flow velocity meter. The 3D-printed platform is angled at 30 degrees to achieve transparent flow visualization, and it doesn't require any external optical components such as external lenses and filters. Two LED modules integrated into the platform create a uniform illumination environment for video capture, powered directly by the smartphone. The performance of our platform, combined with a customized video processing algorithm, was assessed in three different channel types: uniform straight channels, straight channels with varying widths, and vessel-like channel patterns to demonstrate its versatility. Our device effectively measured flow velocities from 5.43 mm/s to 24.47 mm/s, with video quality at 1080p resolution and 60 frames per second, for which the measurement range can be extended by adjusting the frame rate. This flow velocity meter can be a useful analytical tool to evaluate and enhance microfluidic channel designs of various lab-on-a-chip applications.