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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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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; Aydemir, Umut; Faculty Member; Department of Chemistry; 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; Acar, Havva Funda Yağcı; Faculty Member; Department of Chemistry; 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; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; 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 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; Öztuna, Feriha Eylül Saraç; Ünal, Özlem; Acar, Havva Funda Yağcı; Ünal, Uğur; Researcher; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; 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; Kaş, Recep; Sevinç, Esra; Acar, Havva Funda Yağcı; Master Student; Master Student; Faculty Member; Department of Chemistry; 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; Duman, Fatma Demir; Khodadust, Rouhollah; Acar, Havva Funda Yağcı; PhD Student; Other; Faculty Member; Department of Chemistry; 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; Acar, Havva Funda Yağcı; Çelebi, Serdar; Serttunalı, Nazlı İpek; Faculty Member; Master Student; Undergraduate Student; Department of Chemistry; Department of Chemical and Biological Engineering; 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.Publication Metadata only Anticancer use of nanoparticles as nucleic acid carriers(Amer Scientific Publishers, 2014) Gozuacik, D.; Akkoc, Y.; Kosar, A.; Dogan-Ekici, A. Isin; Ekici, Sinan; Department of Chemistry; Acar, Havva Funda Yağcı; Faculty Member; Department of Chemistry; College of Sciences; 178902Advances in nanotechnology opened up new horizons in the field of cancer research. Nanoparticles made of various organic and inorganic materials and with different optical, magnetic and physical characteristics have the potential to revolutionize the way we diagnose, treat and follow-up cancers. Importantly, designs that might allow tumor-specific targeting and lesser side effects may be produced. Nanoparticles may be tailored to carry conventional chemotherapeutics or new generation organic drugs. Currently, most of the drugs that are commonly used, are small chemical molecules targeting disease-related enzymes. Recent progress in RNA interference technologies showed that, even proteins that are considered to be "undruggable" by small chemical molecules, might be targeted by small RNAs for the purpose of curing diseases, including cancer. In fact, small RNAs such as siRNAs, shRNAs and miRNAs can drastically change cellular levels of almost any given disease-associated protein or protein group, resulting in a therapeutic effect. Gene therapy attempts were failing mainly due to delivery viral vector-related side effects. Biocompatible, non-toxic and efficient nanoparticle carriers raise new hopes for the gene therapy of cancer. In this review article, we discuss new advances in nucleic acid and especially RNA carrier nanoparticles, and summarize recent progress about their use in cancer therapy.Publication Metadata only Emergence of 2MPA as an effective coating for highly stable and luminescent quantum dots(American Chemical Society (ACS), 2009) Özen, Can; Lieberwirth, Ingo; Department of Chemistry; N/A; Department of Chemistry; Acar, Havva Funda Yağcı; Kaş, Recep; Yurtsever, İsmail Ersin; Faculty Member; Master Student; Faculty Member; Department of Chemistry; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; 178902; N/A; 71293-Mercaptopropionic acid (3MPA) is a popular coating material for the preparation of aqueous quantum dots, yet its isomer 2-mercaptopropionic acid (2MPA) has not been much studied. Here, we present a detailed study on the aqueous synthesis of CdS quantum dots with a 2MPA coating. Reaction variables Such as the Cd/S ratio, 2MPA/Cd ratio, pH, and temperature were individually studied to evaluate the influence of these variables on particle size and luminescence. At the optimum ratios and reaction conditions, a quantum yield (QY) as high as 54% was achieved. These quantum dots (QDs) have exhibited excellent colloidal and photostability over eight months of study. The color of the emission can be tuned by the reaction temperature and/or Cd/S ratio. 3MPA-coated US nanoparticles were prepared at various 3MPA/Cd ratios for comparison. The highest QY achieved for CdS-3MPA was 15%, and the luminescence decreased dramatically overtime. Ab initio calculations and spectroscopic characterization did not reveal a significant difference in the structure or particle-coating interaction between 2MPA- and 3MPA-coated QDs. Luminesence lifetime measurements indicated longer lifetimes and a larger contribution of the surface-related emission, indicating better removal of quenching defects froth the surface in 2MPA-coated particles compared to that of CdS-3MPA. On the basis of the provided evidence, we report 2MPA as a new and better alternative to the widely used 3MPA for superior luminescence and long-term photo and colloidal stability.Publication Metadata only Mesoporous graphitic carbon nitride/black phosphorus/agpd alloy nanoparticles ternary nanocomposite: a highly efficient catalyst for the methanolysis of ammonia borane(Amer Chemical Soc, 2020) N/A; Department of Chemistry; N/A; Department of Chemistry; Korkut, Sibel Eken; Küçükkeçeci, Hüseyin; Metin, Önder; Researcher; Researcher; Faculty Member; Department of Chemistry; 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; N/A; N/A; 46962A novel ternary nanocomposite, mesoporous graphitic carbon nitride/black phosphorus-AgPd (denoted mpg-CN/BP-AgPd), was successfully fabricated by assembling the as -prepared AgPd alloy nanoparticles (NPs) on mesoporous graphitic carbon nitride/black phosphorus (mpg-CN/BP) binary composites. This novel nanocomposite comprises a heterojunction support material formed by two distinct nonmetallic semiconductors (mpg-CN and BP) with adaptable band gaps and edge voltages, providing enhanced catalytic activity to AgPd alloy NPs in hydrogen generation from the methanolysis of ammonia borane (AB) compared to its single components under the blue light-emitting diode (LED) light illumination. The yielded mpg-CN/BP-AgPd ternary nanocomposites were characterized by many advanced analytical techniques (transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), time-resolved spectroscopy, inductively coupled plasma-mass spectroscopy (ICP-MS), and fourier transform infrared (FTIR), and then they were tested as catalysts in hydrogen generation from the methanolysis of AB at room temperature. Several parameters such as the effect of mpg-CN/BP ratio, alloy composition, and type of the light source were studied to optimize the catalytic activity of the mpg-CN/BP-AgPd nanocomposites in the methanolysis of AB. The best catalytic activity of mpg-CN/BP-AgPd nanocomposites was obtained using an mpg-CN/BP ratio of 5/1 (wt/wt) and Ag50Pd50 alloy composition under the blue LED illumination at room temperature. The activity of the ternary nanocomposites was further enhanced by the acetic acid treatment, and a high initial turnover frequency of 43.7 mol(center dot H-2) mol(catalyst)(-1) min(-1) was reported. Besides their high catalytic activity, the mpg-CN/BP-AgPd nanocomposites were reusable catalysts in the methanolysis of AB. This study also included detailed kinetics of AB methanolysis catalyzed by mpg-CN/BP-AgPd nanocomposites.