Publications without Fulltext
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
Browse
40 results
Search Results
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 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.Publication Metadata only Melt-centrifuged (BI,SB)(2)TE-3: engineering microstructure toward high thermoelectric efficiency(Wiley-V C H Verlag Gmbh, 2018) Pan, Yu; Grovogui, Jann A.; Witting, Ian T.; Hanus, Riley; Xu, Yaobin; Wu, Jinsong; Wu, Chao-Feng; Sun, Fu-Hua; Zhuang, Hua-Lu; Dong, Jin-Feng; Li, Jing-Feng; Dravid, Vinayak P.; Snyder, G. Jeffrey; Department of Chemistry; Department of Chemistry; Aydemir, Umut; Faculty Member; College of Sciences; 58403Microstructure engineering is an effective strategy to reduce lattice thermal conductivity (kappa(l)) and enhance the thermoelectric figure of merit (zT). Through a new process based on melt-centrifugation to squeeze out excess eutectic liquid, microstructure modulation is realized to manipulate the formation of dislocations and clean grain boundaries, resulting in a porous network with a platelet structure. In this way, phonon transport is strongly disrupted by a combination of porosity, pore surfaces/junctions, grain boundaries, and lattice dislocations. These collectively result in a approximate to 60% reduction of kappa(l) compared to zone melted ingot, while the charge carriers remain relatively mobile across the liquid-fused grains. This porous material displays a zT value of 1.2, which is higher than fully dense conventional zone melted ingots and hot pressed (Bi,Sb)(2)Te-3 alloys. A segmented leg of melt-centrifuged Bi0.5Sb1.5Te3 and Bi0.3Sb1.7Te3 could produce a high device ZT exceeding 1.0 over the whole temperature range of 323-523 K and an efficiency up to 9%. The present work demonstrates a method for synthesizing high-efficiency porous thermoelectric materials through an unconventional melt-centrifugation technique.Publication Metadata only A novel magnetomechanical pump to actuate ferrofluids in minichannels(Begell House, Inc, 2011) Bilgin, Alp; Kurtoglu, Evrim; Erk, Hadi Cagdas; Sesen, Muhsincan; Kosar, Ali; Department of Chemistry; Department of Chemistry; Acar, Havva Funda Yağcı; Faculty Member; College of Sciences; 178902An improvement in the current methods of ferrofluid actuation was presented in this paper. A novel magnetomechanical microfluidic pump design was implemented with a ferrofluid as the active working fluid. Obtained flow rates were comparable to previous results in this research line. It was also seen that the basic pump architecture, which the subject pump is based on, enables much more room for further development.Publication Metadata only Nanoparticle silicalite-1 crystallization from clear solutions: nucleation(Elsevier Science Bv, 2009) Tokay, Begüm; Erdem-Şenatalar, Ayşe; Schueth, Ferdi; Thompson, Robert W.; Department of Chemistry; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; College of Sciences; 178882Despite much effort spent by various research groups, there remain many aspects of nanoparticle silicalite-1 crystallization from clear solutions which require further investigation. In order to shed light, especially on the nucleation of silicalite-1, particle growth at 100 degrees C from several starting compositions known to yield colloidal silicalite-1, which have been studied previously by other researchers using various techniques, was followed in this study by laser light scattering using scattering angles of 90 degrees and 173 degrees, and zeta potential and pH measurements. Crystallinity was monitored by X-ray diffraction, Fourier transform infrared analysis and transmission electron microscopy. Thermogravimetric analyses and density measurements were also used to characterize the products obtained at various times during the syntheses. The results demonstrate that the distinct time of sudden jump in the effective diameter of the nanoparticles in solution, as observed more clearly by using the back-scattering device, and which marks the beginning of the constant linear growth rate of the particles, corresponds to the nucleation of the silicalite-1 crystal structure. This time was also shown to coincide with the exo-endo thermal switch time of the reaction mechanism, which has been observed previously by another research group. Nucleation was accompanied by an aggregation of a population of smaller particles, as indicated by the broadening of the particle size distribution, and the variation of the pH and zeta potential values during synthesis.Publication Metadata only Wetting behavior of superhydrophobic poly(methyl methacrylate)(Elsevier Science Sa, 2018) Department of Chemistry; N/A; Department of Chemistry; Department of Chemistry; Yılgör, Emel; Söz, Çağla Koşak; Yılgör, İskender; Researcher; PhD Student; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; 40527; N/A; 24181Superhydrophobic PMMA surfaces were prepared by spin-coating and doctor blade coating of PMAA/hydrophobic silica (1/10 by weight) dispersions in toluene onto glass substrates. Influence of the number of coating layers applied and gauge thickness of the doctor blade used on surface properties were investigated. Formation of dual scale, micro/nano surface topographies were demonstrated by scanning electron microscopy, atomic force microscopy and white light interferometry studies. Roughness factor (r) and average surface roughness (R-a) values of the surfaces were determined. Wetting behavior of superhydrophobic PMMA surfaces obtained by introducing micro-nano, hierarchical roughness to inherently hydrophilic smooth PMMA films cannot be explained by Wenzel model. Therefore, wetting behavior of these surfaces were analyzed using Cassie-Baxter model and area fraction of surface protrusions were estimated.Publication Metadata only Layer-by-layer grown electrodes composed of cationic Fe 3 O 4 nanoparticles and graphene oxide nanosheets for electrochemical energy storage devices(Amer Chemical Soc, 2019) Erdem, Emre; Department of Chemistry; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Öztuna, Feriha Eylül Saraç; Ünal, Özlem; Acar, Havva Funda Yağcı; Ünal, Uğur; Researcher; PhD Student; Faculty Member; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 178902; 42079Ultrathin electrodes composed of layer-by-layer assembled (3-aminopropyl)trimethoxysilane functionalized iron oxide nanoparticles and graphene oxide nanosheets were prepared by a simple and low-cost dip coating method without using any binders or conductive additives. The thickness of the Fe3O4/GO films was simply altered with the number of dip coating cycles. Multilayered films were chemically reduced with hydrazine vapor in order to increase the electrical conductivity. Characterization of multilayer films was performed with scanning transmission electron microscopy, UV-vis spectroscopy, atomic force microscopy, quartz crystal microbalance, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. We have performed cyclic voltammetry and electrochemical impedance spectroscopy for the evaluation of Fe3O4/GO multilayers as possible electrochemical capacitor electrodes. Reduced Fe3O4/GO films exhibit high specific capacitances (varying between 200 and 350 F g(-1) at 5 mV s(-1)), Outperforming the layer-by-layer assembled iron oxides/carbon derivatives (carbon nanotube, graphene).Publication Metadata only A universal method for the preparation of magnetic and luminescent hybrid nanoparticles(American Chemical Society (ACS), 2010) Topal, Uğur; N/A; N/A; Department of Chemistry; Department of Chemistry; Kaş, Recep; Sevinç, Esra; Acar, Havva Funda Yağcı; Master Student; Master Student; Faculty Member; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 178902Hybrid nanoparticles (MDOTs) composed of luminescent quantum dots (QDs) and superparamagnetic iron oxides (SPIOs) were prepared by the ligand-exchange mechanism in a simple and versatile extraction method. In this method, aqueous QDs (CdS or CdTe) coated with carboxylated ligands exchange the fatty acid (lauric acid) coating of SPIOs in a water chloroform extraction process. QDs form a coating around SPIOs and transfer them into the aqueous phase in high efficiency. The method worked successfully with both small and polymeric coating molecules selected as cysteine, 2-mercaptopropionic acid, and a poly(acrylic acid)/mercaptoacetic acid mixture. The original properties of the nanoparticles were well-preserved in the hybrid structures: All MDOTS showed ferrofluidic behavior and had a luminescence in the original color of the QD. Magnetic properties and the luminesence intensity of MDOTs can be easily tuned with the SPIO/QD ratio. All particles are small and show very good stability (optical and colloidal) over months. For stable MDOTs with good luminescence properties, highly luminescent aqueous QDs (CdS or CdTe) with the mentioned coatings were prepared. The first examples of CdTe coated with 2MPA emitting from green to red and CdTe-PAA/MAA were provided as well.Publication Metadata only Folic acid-conjugated cationic Ag2S quantum dots for optical imaging and selective doxorubicin delivery to HeLa cells(Future Medicine Ltd, 2017) Erkısa, Merve; Arı, Ferda; Ulukaya, Engin; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Duman, Fatma Demir; Khodadust, Rouhollah; Acar, Havva Funda Yağcı; PhD Student; Other; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Science and Engineering; College of Sciences; College of Sciences; N/A; N/A; 178902We aim to develop folic acid ( FA)-conjugated cationic Ag2S near-infrared quantum dots (NIRQDs) for the delivery of doxorubicin (DOX) selectively to folate receptor (FR)-positive cancer cells to achieve enhanced drug efficacy and optical tracking in the NIR region. Materials & methods: Cationic Ag2S NIRQDs were decorated with FA using a PEG bridge and loaded with DOX. In vitro studies were performed on FR-positive human cervical carcinoma cells and FR-negative A549 cells. Results: Significantly higher uptake of DOX by human cervical carcinoma cells cells and a greater therapeutic effect along with a strong intracellular optical signal were obtained with DOX-loaded FA-conjugated Ag2S NIRQDs. Conclusion: These Ag2S NIRQDs are promising theranostic nanoparticles for receptor-mediated delivery of DOX with enhanced drug efficacy combined with optical imaging.Publication Metadata only Development of highly stable and luminescent aqueous CdS quantum dots with the poly(acrylic acid)/mercaptoacetic acid binary coating system(Amer Scientific Publishers, 2009) Lieberwirth, I.; Department of Chemistry; N/A; Department of Chemical and Biological Engineering; Department of Chemistry; Department of Chemical and Biological Engineering; Acar, Havva Funda Yağcı; Çelebi, Serdar; Serttunalı, Nazlı İpek; Faculty Member; Master Student; Undergraduate Student; College of Sciences; Graduate School of Sciences and Engineering; College of Engineering; 178902; N/A; N/AHighly stable and luminescent CdS quantum dots (QD) were prepared in aqueous solutions via in situ capping of the crystals with the poly(acrylic acid) (PAA) and mercaptoacetic acid (MAA) binary mixtures. The effect of reaction temperature and coating composition on the particle size, colloidal stability and luminescence were investigated and discussed in detail. CdS QDs coated with either PAA or MAA were also prepared and compared in terms of properties. CdS-MAA QDs were highly luminescent but increasing reaction temperature caused an increase in the crystal size and a significant decrease in the quantum yield (QY). Although less luminescent and bigger than CdS-MAA, CdS-PAA QDs maintained the room temperature size and QY at higher reaction temperatures. CdS-MAA QDs lacked long term colloidal stability whereas CdS-PAA QDs showed excellent stability over a year. Use of PAA/MAA mixture as a coating for CdS nanoparticles during the synthesis provided excellent stability, high QY and ability to tune the size and the color of the emission. Combination of all of these properties can be achieved only with the mixed coating. CdS coated with PAA/MAA at 40/60 ratio displayed the highest QY (50% of Rhodamine B) among the other compositions.