Researcher:
Kaş, Recep

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Master Student

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Recep

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Kaş

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Kaş, Recep

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2009 - 200912010 - 20135

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Researcher Of Publications: search.filters.isAuthorOfPublication.22b4d6de-e238-4fbe-b313-1cdd9233e38f

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Now showing 1 - 6 of 6
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    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; 178902
    Hybrid 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.
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    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; 7129
    3-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.
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    Sonochemical shape control of copper hydroxysulfates
    (Elsevier, 2012) N/A; N/A; N/A; Kaş, Recep; Birer, Özgür; Master Student; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; N/A; N/A; N/A
    Shape control of inorganic nanoparticles generally requires the use of surfactants or ligands to passivate certain crystallographic planes. Additive free shape control methods utilize the differences in the growth rates of crystallographic planes. We combined this approach with the sonochemical method to synthesize copper hydroxysulfate (Brochantite) with morphologies ranging from flowers, to bricks, belts and needles. Sodium peroxydisulfate, which was used as the sulfate and hydroxide source, was decomposed thermally and/or sonically under various pH and temperature conditions. The relative release rates of the sulfate and hydroxide anions determined the final form of the crystals. This technique yielded products even at acidic pH, marking a distinction from the literature reactions, which start with stoichiometric amounts of sulfate and hydroxide anions and yield only a single crystal morphology.
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    Anticorrosion efficiency of ultrasonically deposited silica coatings on titanium
    (Elsevier Science Bv, 2013) N/A; N/A; Department of Chemistry; N/A; Ertan, Fatoş Sibel; Kaş, Recep; Miko, Annamaria; Birer, Özgür; Master Student; Master Student; Teaching Faculty; Researcher; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; 163509; N/A
    We utilized high intensity ultrasound to prepare coatings of silica and organically modified silica composed of multiple layers of densely packed nanoparticles. Ultrasound was used to collide nanoparticles onto an activated titanium surface with high speed. Large areas could be homogeneously coated by this method. These coatings were characterized by spectroscopy and microscopy methods and the anticorrosion efficiency in NaCl solution was evaluated by electrochemical measurements. The results indicated that the composite coatings provided good quality barrier layer on bare titanium and decreased the anodic corrosion rate. It was found that increase in the organic content of the coating shifted the passivation potential towards more positive direction. The comparison of the impedance results recorded at the corrosion potential pointed out that in each case a good quality barrier layer was formed on the titanium surface. The outstanding corrosion resistance of the composite coatings with only similar to 200 nm thickness shows that ultrasound assisted deposition can be a competitive method to obtain corrosion protective layers. (c) 2013 Elsevier B.V. All rights reserved.
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    Ultrasound assisted deposition of silica coatings on titanium
    (Elsevier, 2012) N/A; N/A; N/A; N/A; Kaş, Recep; Ertaş, Fatma Sinem; Birer, Özgür; Master Student; Master Student; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; N/A; N/A; N/A
    We present a novel ultrasound assisted method for silica coating of titanium surfaces. The coatings are formed by "smashing" silica nanoparticles onto activated titanium surface in solution using intense ultrasonic field. Homogeneous silica coatings are formed by deposition of dense multiple layers of silica nanoparticles. Since the nanoparticles also grow during the reaction, the layers of the coatings have smaller particles on the substrate and larger particles towards the surface. The thickness of the coatings can be controlled with several experimental parameters. Silica layers with thickness over 200 nm are readily obtained.
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    Sonochemical synthesis and electrochemical characterization of alpha-nickel hydroxide: precursor effects
    (Springer, 2013) N/A; N/A; Department of Chemistry; N/A; Ertaş, Fatma Sinem; Kaş, Recep; Ünal, Uğur; Birer, Özgür; Master Student; Master Student; Faculty Member; Researcher; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 42079; N/A
    Sonochemical degradation of urea was employed to synthesize alpha-nickel hydroxide from different nickel salts. Utilization of ultrasound yielded products with properties significantly different than the products obtained by thermal degradation of urea. the effect of intercalating chloride, nitrate, Acetate, and sulfate anions on morphology and electrochemical performance was studied. the sulfate-intercalated sample had the smallest interlayer spacing when obtained by the sonochemical method, contradicting all the previous thermal synthesis results. the specific capacitance trend also differed from the literature values, and the value for the sulfate-intercalated sample was larger than that of acetate-and nitrate-intercalated samples. Ultrasonic synthesis increased the specific capacitance of the sulfate-intercalated sample significantly. This sample was also the most reversible and had the highest charge efficiency.