WoS
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14411/18
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Article Citation - WoS: 18Citation - Scopus: 19Synthesis and Enhanced Photocatalytic Activity of Nitrogen-Doped Triphasic Tio<sub>2</Sub> Nanoparticles(Elsevier Science Sa, 2019-05) Erdogan, Nursev; Bouziani, Asmae; Park, Jongee; Micusik, Matej; Kim, Soo Young; Majkova, Eva; Ozturk, AbdullahTiO2 nanoparticles of the single anatase phase, binary anatase-brookite phases, and ternary anatase-brookite-rutile phases were synthesized using an HNO3-catalyzed hydrothermal process. The types and amounts of phases varied depending on the hydrothermal synthesis conditions. The results revealed that N dissolves in different amounts and chemical states, depending on the phases present and their proportions in the nano particles. Brookite and rutile nanoparticles oriented through one direction were found to be crystallized by the surface transformation from anatase. Photocatalytic activity tests, evaluated by degradation of methylene blue (MB) under ultraviolet (UV) and visible light illumination, revealed that the N-doped TiO2 nanoparticles containing a ternary-phase mixture had the best photocatalytic activity. The MB degradation of the visible light-active nanoparticles was three times better than that of a commercially available well-known TiO2 powder, P25 under UV illumination. The enhanced photoactivity was attributed to the following: i) a high surface area, ii) suppression of the recombination of electron-hole pairs with ternary-phase mixture crystallized in heterojunctions, iii) larger anatase phase content, and iv) narrower band gap and facilitation of charge separation by dissolved N atoms.Article Citation - WoS: 51Citation - Scopus: 57Synthesis of Α-fe<sub>2</Sub>o<sub>3< Heterogeneous Composites by the Sol-Gel Process and Their Photocatalytic Activity(Elsevier Science Sa, 2020-09) Bouziani, Asmae; Park, Jongee; Ozturk, Abdullahalpha-Fe2O3/TiO2 heterogeneous composites were synthesized by the sol-gel process to increase the photocatalytic activity of TiO2. The structural, morphological, and optical characteristics of the composites were determined by X-ray diffraction, scanning electron microscope, and UV-vis diffuse reflectance spectroscopy. Results revealed that the incorporation of alpha-Fe2O3 to TiO2 widened the visible light absorption ability of TiO2. It was realized that the calcination temperature plays a crucial role in morphology development hence photocatalytic activity of the alpha-Fe2O3/TiO2 heterogeneous composites. The photocatalytic activity of the composites calcined at various temperatures was evaluated for the degradation of Methylene Blue (MB) and Phenol (Ph) in aqueous medium under UV and sun-like illuminations. The alpha-Fe2O3-TiO2 composites exhibits superior photocatalytic efficiency to degrade both MB and Ph as compared to both pristine TiO2 and pristine alpha-Fe2O3 under sun-like illumination. The alpha-Fe2O3/TiO2 composite degraded approximately 90 % of MB and 50 % of Ph in 180 min sun-like illumination. Improvement in photocatalytic activity is attributed to the separation of photogenerated electron/hole pairs through the interaction of alpha-Fe(2)O(3 )and TiO2.Article Citation - WoS: 6Citation - Scopus: 7An Electrochromic Polymer Based on Cyclopenta[2,1-B;3,4 Effect of a Single Atom Alteration on the Electrochemical and Optical Properties of the Polymer Backbone(Elsevier Science Sa, 2020-07) Tutuncu, Esra; Varlik, Bengisu; Kesimal, Busra; Cihaner, Atilla; Ozkut, Merve Icli; Icli Ozkut, MerveAn electrochromic polymer, namely "poly(2,6-(3,3-didecyl-3,4-dihydro-2H-thieno [3,4-b] [1,4]dioxepin-6-yl)-4,4-dioctyl-4H-cyclopenta[2,1-b;3,4-b']dithiophene)" (P1), was electrochemically synthesized successfully, and its electrochemical and optical properties were investigated. The band gap of the polymer P1 was calculated as 1.77 eV with -5.45 eV Highest Occupied Molecular Orbital (HOMO) and -3.68 eV Lowest Unoccupied Molecular Orbital (LUMO) energy levels. The polymer P1 is bluish purple when neutralized and highly transparent greenish purple when oxidized. This color change was observed around 1.4 s between its redox states and optical contrast ratio was found to be as 49 % and 53 % with 234 cm(2)/C and 239 cm(2)/C coloration efficiencies at 590 nm and 634 nm, respectively. Moreover, the properties of this polymer were compared to its analogues and also during this comparison the effect of alteration of a single atom in the pendant unit was tried to be understood.Article Citation - WoS: 29Citation - Scopus: 31Composition-tuned band gap energy and refractive index in GaS<sub>x</sub>Se<sub>1-x</sub> layered mixed crystals(Elsevier Science Sa, 2017-04) Isik, Mehmet; Gasanly, NizamiTransmission and reflection measurements on GaSxSe1-x mixed crystals (0 <= x <= 1) were carried out in the 400-1000 nm spectral range. Band gap energies of the studied crystals were obtained using the derivative spectra of transmittance and reflectance. The compositional dependence of band gap energy revealed that as sulfur (selenium) composition is increased (decreased) in the mixed crystals, band gap energy increases quadratically from 1.99 eV (GaSe) to 2.55 eV (GaS). Spectral dependencies of refractive indices of the mixed crystals were plotted using the reflectance spectra. It was observed that refractive index decreases nearly in a linear behavior with increasing band gap energy for GaSxSe1-x mixed crystals. Moreover, the composition ratio of the mixed crystals was obtained from the energy dispersive spectroscopy measurements. The atomic compositions of the studied crystals are well-matched with composition x increasing from 0 to 1 by intervals of 0.25. (C) 2016 Elsevier B.V. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 6Nonlinear Error Correction Based Cointegration Test in Panel Data(Elsevier Science Sa, 2017-08) Omay, Tolga; Emirmahmutoglu, Furkan; Denaux, Zulal S.We propose a nonlinear error correction-based cointegration test in a panel data setting and provide their small sample properties. (C) 2017 Elsevier B.V. All rights reserved.Article Citation - WoS: 48Citation - Scopus: 48Global Risk Aversion and Emerging Market Return Comovements(Elsevier Science Sa, 2018-12) Demirer, Riza; Omay, Tolga; Yuksel, Asli; Yuksel, AydinUtilizing the recently developed measure of global risk aversion by Xu (2017), we show that global risk aversion is a significant determinant of international equity correlations, consistently across all emerging markets examined. The positive effect of risk aversion on emerging market comovements is particularly strong for South Africa and Turkey and is consistent with contagion effects. The results underscore the importance of non-cash flow shocks in models of contagion and portfolio risk. (C) 2018 Elsevier B.V. All rights reserved.Article Citation - WoS: 24Citation - Scopus: 27Nanocrystalline Metal Organic Framework (mil-101) Stabilized Copper Nanoparticles: Highly Efficient Nanocatalyst for the Hydrolytic Dehydrogenation of Methylamine Borane(Elsevier Science Sa, 2018-11) Baguc, Ismail Burak; Ertas, Ilknur Efecan; Yurderi, Mehmet; Bulut, Ahmet; Zahmakiran, Mehmet; Kaya, MuratThe copper nanoparticles stabilized by nanocrystalline MIL-101 framework (Cu/nano-MIL-101) was reproducibly prepared by following double solvent method combined with liquid phase chemical reduction technique. The characterization of the resulting new material was done by using various analytical techniques including ICP-OES, P-XRD, N-2-adsorption-desorption, XPS, FE-SEM, SEM-EDX, BFTEM and HAADF-STEM; the summation of their results reveals that the formation of well-dispersed and very small sized (0.8 nm) copper nanoparticles within nanocrystalline MIL-101 framework. The catalytic performance of Cu/nano-MIL-101 in terms of activity and stability was tested in the hydrolytic dehydrogenation of methylamine borane (CH3NH2BH3), which has been considered as one of the attractive materials for the efficient chemical hydrogen storage. Cu/nano-MIL-101 catalyzes the hydrolytic dehydrogenation of methylamine borane with high activity (turnover frequency; TOF = 257 mot H-2/mol Cu x h) and conversion ( > 99%) under air at room temperature. Moreover, these nano-MIL-101 framework stabilized copper nanoparticles show great durability against to sintering and leaching, which make Cu/nano-MIL-101 reusable nanocatalyst in the hydrolytic dehydrogenation of methylamine-borane. Cu/nano-MIL-101 nanocatalyst retains 83% of its inherent activity at complete conversion even at 10th recycle in the hydrolytic dehydrogenation of methylamine borane.Article Citation - WoS: 6Citation - Scopus: 5Growth and Characterization of Pbmo0.75w0.25o4 Single Crystal: a Promising Material for Optical Applications(Elsevier Science Sa, 2023-02) Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.The present paper reports the structural and optical properties of PbMo0.75W0.25O4 single crystals grown by Czochralski method. XRD pattern of the crystal indicated well-defined two diffraction peaks associated with tetragonal crystalline structure. Raman and infrared spectra of the grown single crystals were presented to get information about the vibrational characteristics. Observed Raman modes were associated with modes of PbMoO4 and PbWO4. Eight bands were revealed in the infrared spectrum. The bands observed in the spectrum were attributed to multiphonon absorption processes. Transmission spectrum was measured in the 375-700 nm spectral region. The analyses of the spectrum resulted in direct band gap energy of 3.12 +/- 0.03 eV. The compositional dependent band gap energy plot was drawn considering the reported band gap energies of PbMoO4, PbWO4 and revealed band gap of PbMo0.75W0.25O4 single crystal. An almost linear behavior of composition-band gap energy was seen for PbMo1-xWxO4 compounds. Urbach energy was also found from the absorption coefficient analysis as 0.082 +/- 0.002 eV.Article Citation - WoS: 3Citation - Scopus: 3D-A Type Conjugated Polymers in Dual Electrochromic Devices Tuning From Green To Blue Colors(Elsevier Science Sa, 2023-07) Ozkut, Merve Icli; Onal, Ahmet M.; Cihaner, Atilla; Icli Ozkut, MerveIn this study, the electrochemical and electro-optical properties of four different dual electrochromic devices were unraveled. In all devices, soluble donor-acceptor-donor (D-A-D) type conjugated electrochromic polymers based on didecyl substituted 3,4-propylenedioxythiophene and heterodiazole analogs were used, and they were coated on ITO electrochemically for the construction of the electrochromic devices. Because all D-A-D polymers and PEDOT are colorful in their neutral states and colorless in their oxidized states, it is possible to observe one -to-one colors of pure two polymers in their electrochromic devices rather than a mixture of colors. It was observed that devices changed their colors from the tunes of green to blue under applied external voltage. Switching times, coloration efficiencies and stabilities of the electrochromic devices were calculated as ranging from 1.0 to 6.0 s, 133-544 cm2/C and 54-91 %, respectively, after 5000 cycles. The P(PSeP-C10)-P(PNP-C10) device showed the highest coloration efficiency (544 cm2/C) as well as the best optical and electrochemical stabilities among the electrochromic devices after 5000 cycles (91 % and 92 %, respectively).Article Citation - WoS: 9Citation - Scopus: 10Electronic, Optical and Thermodynamic Characteristics of Bi12sio20 Sillenite: First Principle Calculations(Elsevier Science Sa, 2021-07) Isik, M.; Surucu, G.; Gencer, A.; Gasanly, N. M.Bi12XO20 (X: Si, Ge, Ti) ternary semiconducting compounds are known as sillenites and take a remarkable attention thanks to their attractive photorefractive properties. The present paper reports electronic, optical and thermodynamic characteristics of Bi12SiO20 by means of density functional theory (DFT) calculations. The crystalline structure of the compound was revealed as cubic with lattice constant of 10.135 angstrom. XRD pattern obtained from DFT calculations were compared with experimental data and there is a good consistency between them. The electronic band structure and density of state plots were presented in detail. The band gap energy of the compound was determined from electronic band structure and spectra of optical constants. The spectral dependencies of real and imaginary components of dielectric function, refractive index, extinction coefficient, absorption coefficient and loss function were plotted in the 0-12 eV spectral range. The revealed structural, electronic and optical characteristics were discussed taking into account the previously reported theoretical and experimental studies on the Bi12SiO20 sillenite.
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