Browsing by Author "CİHANER, Atilla"
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thesis.listelement.badge PREPARATION AND CHARACTERIZATION OF PALLADIUM-COPPER BIMETALLIC NANOPARTICLES SUPPORTED ON SILICA COATED COBALT FERRITE MAGNETIC PARTICLES FOR HYDROLYTIC DEHYDROGENATION OF AMMONIA BORANE(2015-06-25) AL-AQBI, Talaat Hikmat Hashim; KAYA, Murat; CİHANER, AtillaMetal nanoparticles have attracted much attention over the last decade due to their desired applications in catalytic systems and the usage of these particles in such systems are considered to be a promising way for bridging homogenous and heterogenous catalysis, that is to say for “quasihomogeneous” (or soluble heterogeneous) systems. Naked nanoparticles are due to high surface energy not stable and prone to coagulate while catalytic transformation is taking place. On the other hand, filtration techniques are not efficient to separate nanoparticles that have diameters of less than 100 nm. Under such circumstances, expensive ultracentrifugation is preferred to separate the product and catalyst. In order to get rid of the disadvantages of naked nanoparticles and to enhance the stability and to obtain reusable catalysts, immobilization of nanoparticles onto inorganic supports provide the desired properties for catalytic efficiency. Due to high hydrogen storage capacity (19.6 % wt) and low molecular weight, the innovations in the development of nanocomposite catalysts for the hydrolytic dehydrogenation of ammonia-borane (NH3BH3) is essential to use these catalysts as solid hydrogen carrier. In this thesis, new and reproducible catalyst system consists of palladium-copper bimetallic nanoparticles supported on silica coated magnetic particles has been prepared by wet-impregnation method. After addition of Pd2+ and Cu2+ ions on silica coated cobalt ferrite nanoparticles, nanoparticles formed by in situ reduction of the Pd2+ and Cu2+ ions with NH3BH3 on the surface of silica coated magnetic nanoparticles. The characterization of nanocomposite catalysts were done by inductively coupled plasma/optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high resolution- transmission electron microscopy (HR-TEM) and N2 adsorption–desorption technique. Palladium-Copper bimetallic nanoparticles supported on silica coated cobalt ferrite (PdCuNPs/SiO2-CoFe2O4) provide an initial turnover frequency (TOF) of 238 min-1 at room temperature that shows higher catalytic activity than both non-noble metal catalysts and noble metal based homogenous and heterogeneous catalysts that is used in the reaction of hydrolytic dehydrogenation of ammonia-borane. One of the most important opportunity of such catalyst system is that, catalysts can be collected with a magnet in the reactor wall and they are reusable for up to 5 recycles with the sustainable catalytic activity that exhibited excellent reusability of the catalyst.thesis.listelement.badge PREPARATION AND CHARACTERIZATION OF SILVER-PESeE FILM DEPOSITED ON ITO GLASS SURFACE AS A SURFACE ENHANCED RAMAN SCATTERING SUBSTRATE(2015-06-25) ALSHUWAİLİ, Kadhim Taresh Raisan; KAYA, Murat; CİHANER, AtillaSurface enhanced Raman scattering (SERS) is known as a very attractive technique for the characterization and detection of a variety of chemical and biological molecules due to their impressive characteristics such as giving spectral fingerprint of vibrations, high sensitivity and insensitivity to water. One of the most important points of the SERS technique is the requirement for producing a substrate having an ideal surface morphology to facilitate the achievement of the most favorable enhancement. Here a novel, simple, reliable, and reproducible one-step electrochemical method for the preparation of surface enhanced Raman-active polymer-mediated silver nanoparticles (Ag NPs) on planar indium tin oxide (ITO) coated glass substrates was reported. Poly (4,7-di-2,3-dihydrothieno [3,4-b] [1,4] dioxin-5-yl-2,1,3 benzoselena diazole) (PESeE) film was used as a support material for dispersing silver nanostructures on the surface homogeneously. The morphologies of the prepared substrates have been investigated by field emission scanning electron microscopy (FE-SEM). The effect of the thickness of PESeE polymer film and the amount of silver particles on the polymer film on the SERS response were studied as well as repeatability and stability of prepared substrates. Brilliant cresyl blue (BCB) has been used as Raman probes to evaluate the properties of the new SERS substrates.thesis.listelement.badge SYNTHESIS AND CHARACTERIZATION OF A NEW SELENOPHENE BASED ELECTROCHROMIC POLYMER(2015-01-31) KARABAY, Barış; CİHANER, AtillaA new derivative of 3,4-propylenedioxyselenophene bearing naphtyl appendages on the bridge, called 3,4-dihydro-3,3-bis ((naphthalen-1-yl)methyl)-2H selenopheno[3,4-b][1,4]dioxepine (ProDOS-Np2), was synthesized and polymerized via potentiostatic and potentiodynamic methods. Electrochemically obtained polymer film (PProDOS-Np2) is pure blue at the neutral state and highly transparent at the oxidized state. An increase in the size of the substituents on the bridge resulted in an increase in the optical contrast ratio. Upon moving from naked bridge to benzyl and to naphtyl substituents on the bridge center, the optical contrast changed from 51% to 65% and finally to 84%. When compared to polythiophene analogue, the PProDOS Np2 has lower oxidation potential and band gap, higher optical contrast ratio, coloration efficiency, robustness and stability. The polymer film preserved its properties even after thousands of cycles under ambient conditions.thesis.listelement.badge SYNTHESIS AND CHARACTERIZATION OF NEW DITHIENOSILOLE BASED CHROMIC POLYMERS(2015-06-27) AL-JUMAILI, MOHAMMED; CİHANER, Atilla2-Ethylhexyl substituted dithienosilole based soluble polymers including thiophene (P1) and bithiophene (P2) units were synthesized via Stille Coupling reaction. The polymers were characterized by using nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA) techniques. The presence of 2- ethylhexyl substituents on the silole ring gave solubility property to the polymers in common solvents. According to GPC measurements, weight average molecular weights of the polymers P1 and P2 were found to be as 70977 with a polydispersity index (PDI) of 2.30 and 110439 with a PDI of 1.42, respectively. Fluorescent polymers in toluene solution have maximum emisssion bands at 634 nm for P1 and 613 for P2. Chemical and electrochemical doping of the polymers in solution and film forms were monitored by using ultraviolet-visible (Uv-vis) spectroscopic technique. The polymers exhibited chromic (chemochromic and electrochromic) properties. While the colors of the neutral polymer films are purple for P1 and reddish brown for P2, both polymers are transparent sky blue at their oxidized states. The band gaps of polymers in film forms were calculated as 1.81 eV for P1 and 1.92 eV for P2. Also, electrochromic device applications of the polymers were done. Electrochemical and optical behaviors of the polymer demonstrated that they can be good candidates for optoelectronic applications.thesis.listelement.badge SYNTHESIS AND CHARACTERIZATION OF NEW POLYMERIC MATERIALS FROM ELEMENTAL SULFUR(2015-06-26) SALMAN, Mohamed Khalifa; CİHANER, AtillaNew elemental sulfur based polymeric materials called poly(sulfur-random divinylbenzene) (poly(S-r-DVB)) were synthesized by ring opening polymerization in the presence of a mixture of o-, m- and p-diviniylbenzene (DVB) as a crosslinker. In order to get the copolymers, the elemental sulfur was melted at 160 oC and therefore ring-opening polymerization of the S8 was promoted and a clear yellow/orange colored liquid was obtained. Then, various amounts of DVB were added to this liquid directly via a syringe and continued to further mixing at 200 oC for 10 minutes to get viscous reddish brown polymeric materials. The copolymers are soluble in common solvents like tetrahydrofuran, dichloromethane and chloroform, and they can be coated on any surface as thin film. The characterization of the materials were performed by using nuclear magnetic resonance, fourier transform infrared and Raman spectroscopies. The morphological properties were monitored via scanning electron microscope technique. Thermal analysis showed that an increase in the amount of DVB in the copolymers resulted in an increase in the termal decomposition temperature. On the other hand, poly(S-r-DVB) copolymers exhibited good percent transmittance as 50 %T between 1500 and 13000 nm in electromagnetic radiation spectrum, which make them good candidates to be amenable use in military and surveillance cameras.thesis.listelement.badge SYNTHESIS AND POLYMERIZATION OF BENZIMIDAZOLE BASED MONOMERS VIA A DONOR – ACCEPTOR APPROACH(2015-06-25) AL-OGAİDİ, Saad; CİHANER, AtillaA new series of fluorescent donor-acceptor-donor (D-A-D) type monomers based on benzimidazole acceptor unit bearing cycloalkane appendages, called 4,7-di-2,3- dihydrothieno[3,4-b][1,4]dioxin-5-ylspiro[benzimidazole-2,1'-cyclopentane] (E5E), 4,7-di-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-ylspiro[benzimidazole-2,1'- cyclohexane] (E6E) and 4,7-di-2-thienylspiro[benzimidazole-2,1'-cyclohexane] (T6T), were synthesized and polymerized via potentiostatic and potentiodynamic methods. The effect of ring size on benzimidazole unit and the kind of donor moiety in D-A-D system has been studied systematically on the electrochemical and optical properties. The optical studies showed that ring size of the benzimidazole unit has no effect on the absorbance and fluorescence properties, whereas the oxidation potential of E5E, E6E and T6T monomers varied with respect to both the ring size and donor unit: 0.89 V, 0.83 V and 1.22 V vs Ag/AgCl, respectively. All polymers have ambipolar (p- and n-type doping) and electrochromic properties. While the polymer films PE5E and PE6E are green at neutral state and transparent at oxidized state, the polymer PT6T has no appreciable color change between its neutral and oxidized state. The polymers bearing 3,4-ethylenedioxythiophene unit as donor units (PE5E and PE6E) exhibited lower band gap values (1.21 eV and 1.18 eV, respectively) than PT6T (1.53 eV). When compared to PT6T, PE5E and PE6E polymers are more stable under ambient condition. While PE5E retained 76% of its electroactivity after 4000 cycles, PE6E has 65% of its electroactivity after 2000 cycles.Item TÜRKİYE'DE TEMEL BİLİMLERİN ÇÖKÜŞÜ(Bilim ve Teknoloji, 2015-11-09) CİHANER, AtillaÖncelikle Türkiye'nin bugünkü bilim ve teknolojideki konumunu görmek ve kat ettiği mesafeyi anlayabilmek için, Türkiye'nin geçmişten bugüne olan bilim ve teknolojinin üç ayağı olarak nitelendirebileceğimiz, bilim politikalarını, bilim üretimini ve bilim anlayışını kısaca göz atmakta fayda var. Osmanlı'daki Batılılaşma, modernleşme ve yenileşme hareketleri 17. yy'ın sonlarına doğru başlayıp (1683 Viyana bozgunu sonrası) 18. yy'ın ilk yarısına kadar sürer. Lale Devri, ilk matbaa'nın kullanımı, II. Mahmut Devri, III. Selim Devri, Tanzimat, vb. olaylar Osmanlı'ını Batılılaşma ve modernleşme serüvenindeki önemli olaylardan birkaçıdır.Item TÜRKİYE’DE TEMEL BİLİMLERİN ÇÖKÜŞÜ(Bilim ve Teknoloji, 2015-11-09) CİHANER, AtillaÜniversitelerdeki ilk çöküşün habercisi, temel bilimler kontenjanında yaşanan sıkıntılar ve kapanan bölümler olmuştur. Yürütülen bilim politikalarının yanlışlığından kaynaklı olarak son yıllarda boş kontenjanlarla gündemde olan temel bilimler programlarıyla ilgili çalışma başlatan YÖK, 2014 yılında 11’den az öğrenci kaydolan devlet üniversitelerindeki programlara artık kontenjan verilmeyeceğini duyurmuştur. Uygulanan bilim politikasının yanlışlığını 2010 yılında üniversitelerin temel bilimler bölümlerine ayrılan kontenjan sayılarından net olarak anlamak mümkündür. Bir yıl öncesinde mevcut kontenjanlar doldurulmamış olmasına rağmen kontenjan sayıları arttırılırken bu bölümlere yerleşen öğrenci sayılarında dramatik bir düşüş görülmüştür. YÖK’ün kontenjan verilmeyeceğine dair yaptığı açıklama bir domino etkisi yaratmış ve sonraki yıllarda temel bilimler bölümleri bir bir kapanmaya başlamıştır.