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Öğe 1D Amorphous Tungsten-Based Ternary Refractory Metal Sulfides for Catalytic Hydrogen Evolution at Soft Interfaces(WILEY-V C H VERLAG GMBH, 2019) Aslan, Emre; Sarilmaz, Adem; Ozel, Faruk; Patir, Imren Hatay; Girault, Hubert H.Transition metals incorporated into molybdenum sulfide and tungsten sulfide matrixes are promising candidates for hydrogen evolution due to the unique chemical and physical properties. Here, we first describe a general strategy for the synthesis of rod-like ternary refractory metal sulfides (MWSx; M=Ni, Co, Fe and Mn) through a simple hot-injection method. The newly developed materials are affirmed as valuable alternatives to noble metal Pt due to their simple fabrication, inexpensive and impressive catalytic performance. We present that highly efficient catalysts for the hydrogen evolution at a polarized water/1,2-dichloroethane (DCE) interface by using the decamethylferrocene (DMFc). Kinetics of hydrogen evolution studies are monitored by two phase reactions using UV/Vis spectroscopy, and also further proved by gas chromatography. These ternary refractory metal sulfide catalysts show high catalytic activities on hydrogen evolution comparable to platinum. The rate of hydrogen evolution for the MWSx catalysts changed in the order Ni>Co>Fe>Mn according to the type of first row transition metals.Öğe Chemical and Physical Modification of Surfaces(WILEY-V C H VERLAG GMBH, 2017) Karaman, Mustafa; Gursoy, Mehmet; Kus, Mahmut; Ozel, Faruk; Yenel, Esma; Sahin, Ozlem G.; Kivrak, Hilal D.[Abstract not Available]Öğe Colloidal CuZnSnSe4-xSx nanocrystals for hybrid solar cells(ELSEVIER, 2015) Kus, Mahmut; Ozel, Faruk; Buyukcelebi, Sumeyra; Aljabour, Abdalaziz; Erdogan, Aysenur; Ersoz, Mustafa; Sariciftci, Niyazi SerdarWe report the synthesis of different colloidal CZTSe(4-x)S(x) nanocrystals and their performance in [6,6]-phenyl C61 butyric acid methyl ester (PCBM) based organic/inorganic hybrid bulk heterojunction solar cells. Synthesis of colloidal CuZnSnSe4-xSx were performed and characterized by XRD, TEM, SEM, UV-Visible absorption techniques. Electrochemical and photovoltaic properties were investigated. The best device concept, ITO/PEDOT:PSS/CZTS:PCBM blend (1:10)/Al, showed 280 mu A/cm(2) short circuit current, I-sc with 300 mV open circuit voltage V-oc, and fill factor FF of 0.38. (C) 2014 Elsevier B.V. All rights reserved.Öğe A comparative study on fabrication of Cu2ZnSnS4 (CZTS) nanofibers using acetate and chloride metal precursors(SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2015) Buyukbekar, Burak Zafer; Ozel, Faruk; Sakalak, Huseyin; Cavusoglu, Halit; Ersoz, Mustafa; Kus, Mahmut; Yavuz, Mustafa SelmanThis study reports, for the first time, the fabrication of electrospun Cu2ZnSnS4 (CZTS) nanofibers using metal acetate precursors. Viscous poly(vinyl pyrrolidone) (PVP) solution containing acetate or chloride salts of copper, zinc, and tin was electrospun onto a conductive substrate. The PVP nanofibers that have a mixture of metal salts were annealed at elevated temperatures. After calcination, these nanofibers were treated with the sulfur source and then annealed again in order to generate CZTS nanofibers. The CZTS nanofibers generated from acetate and chloride salts were characterized and compared. Belt-like and wire-like nanofibers were obtained when using metal acetate and chloride precursors, respectively.Öğe Dye-Sensitized Cu2XSnS4 (X=Zn, Ni, Fe, Co, and Mn) Nanofibers for Efficient Photocatalytic Hydrogen Evolution(WILEY-V C H VERLAG GMBH, 2016) Gonce, Mehmet Kerem; Aslan, Emre; Ozel, Faruk; Patir, Imren HatayThe photocatalytic hydrogen evolution activities of low-cost and noble-metal-free Cu2XSnS4 (X=Zn, Ni, Fe, Co, and Mn) nanofiber catalysts have been investigated using triethanolamine as an electron donor and eosinY as a photosensitizer under visible-light irradiation. The rates of hydrogen evolution by Cu2XSnS4 (X=Zn, Ni, Fe, Co, and Mn) nanofibers have been compared with each other and with that of the noble metal Pt. The hydrogen evolution rates for the nanofibers change in the order Cu2NiSnS4>Cu2FeSnS4>Cu2CoSnS4>Cu2ZnSnS4>Cu2MnSnS4 (2028, 1870, 1926, 1420, and 389molg(-1)h(-1), respectively). The differences between the hydrogen evolution rates of the nanofibers could be attributed to their energy levels. Moreover, Cu2NiSnS4, Cu2FeSnS4, and Cu2CoSnS4 nanofibers show higher and more stable photocatalytic hydrogen production rates than that of the noble metal Pt under long-term irradiation with visible light.Öğe Earth-Abundant Cu2CoSnS4 Nanofibers for Highly Efficient H-2 Evolution at Soft Interfaces(WILEY-V C H VERLAG GMBH, 2015) Ozel, Faruk; Yar, Adem; Aslan, Emre; Arkan, Emre; Aljabour, Abdalaziz; Can, Mustafa; Patir, Imren HatayCu2CoSnS4 (CCTS) nanofibers have been fabricated by electrospinning and exhibit an excellent morphology with an average nanofiber diameter of 150 nm. Polyacrylonitrile (PAN) was used as templating polymer that leads to a decrease in imperfections in the crystalline nanofibers. CCTS and Cu2ZnSnS4 (CZTS) nanofibers, based on abundant and environmental friendly elements, efficiently enhanced the rates of biphasic proton reduction in the presence of an organic solubilized electron donor, decamethylferrocene (DMFc). This work paves the way for the exploration of copper-based chalcogenides as electrocatalysts for the hydrogen evolution reaction to replace noble metal Pt.Öğe Electrospinning of Cu2ZnSnSe4-xSx nanofibers by using PAN as template(ELSEVIER SCIENCE BV, 2015) Ozel, Faruk; Kus, Mahmut; Yar, Adem; Arkan, Emre; Yigit, M. Zeliha; Aljabour, Abdalaziz; Buyukcelebi, SumeyraWe firstly demonstrate the synthesis of Cu2ZnSnSe4-xSx (CZTSeS) nanofibers through versatile electrospinning technique. Polyacrylonitrile (PAN) was used as templating polymer that leads to decrease in imperfections on crystal fibers and yields outstanding structure including a few defects with diameter around 250 nm. Sulfurization and/or selenization processes were carried out separately and simultaneously depending upon the demanded chemical structure. Detailed characterization and electrochemical response indicate their potential application for solar cells as p-type semiconductors. (C) 2014 Elsevier B.V. All rights reserved.Öğe Fabrication of Cu2ZnSnS4 (CZTS) nanofibers via electrospinning(AMER CHEMICAL SOC, 2014) Buyukbekar, Burak Zafer; Ozel, Faruk; Sakalak, Huseyin; Kus, Mahmut; Yavuz, Mustafa Selman[Abstract not Available]Öğe Fabrication of quaternary Cu2FeSnS4 (CFTS) nanocrystalline fibers through electrospinning technique(SPRINGER, 2015) Ozel, Faruk; Kus, Mahmut; Yar, Adem; Arkan, Emre; Can, Mustafa; Aljabour, Abdalaziz; Varal, Nurhan MehmetCopper-based quaternary chalcogenide Cu2FeSnS4 (CFTS) is an important material due to its indium-free nature and presence of earth-abundant elements. Herein, CFTS nanofibers have been first fabricated via a facile two-step approach using a simple and inexpensive electrospinning technique. X-ray diffraction and scanning electron microscopy techniques were used to determine structural, morphological, and compositional features of the obtained films. Nanofibers annealed at 500 degrees C for 1 h were characterized by (112), (200), (220), (312) preferred orientations via X-ray diffraction method. Nanofibers showed well crystallization and tetragonal phase. The average diameters of obtained fibers were found to be 100 +/- 50 nm. Cyclic voltammograms showed that CFTS fibers showed p-type behavior.Öğe Hydrogen Evolution Catalyzed by Cu2WS4 at Liquid-Liquid Interfaces(AMER CHEMICAL SOC, 2016) Ozel, Faruk; Aslan, Emre; Sarilmaz, Adem; Patir, Imren HatayThe present study reports, for the first time, both a facile synthesis for ternary Cu2WS4 nanocubes, which were synthesized by a simple and low-cost hot-injection method, and the hydrogen evolution reaction at a biomembrane-like polarized water/1,2-dichloroethane interface catalyzed by Cu2WS4 nanocubes. The rate of hydrogen evolution reaction is increased by about 1000 times by using Cu2WS4 nanocubes when compared to an uncatalyzed reaction.Öğe The influence of CdS quantum dots incorporation on the properties of CdO thin films(EDP SCIENCES S A, 2013) Gultekin, Aytac; Karanfil, Gamze; Ozel, Faruk; Kus, Mahmut; Say, Ridvan; Sonmezoglu, SavasThe aim of our work is to obtain nano-structured cadmium oxide (CdO) thin films by sol-gel spin coating method and to investigate the effects of cadmium sulfide quantum dots (CdS QDs) doping on the structural modification and surface morphology evolution. X-ray diffraction (XRD) results show that the intensities of the peaks of the crystalline phase increase with the increase in CdS QDs concentrations. From scanning electron microscopy (SEM) images, the distinct variations in the morphology of the thin films were also observed. In addition, the evolution of surface morphology, roughness and granularity has been characterized by atomic force microscopy (AFM). Moreover, we have performed the optical characteristics of the thin films such as transparency, energy band gap and Urbach tail. The optical band gap of the thin films increases from 2.23 to 2.51 eV with the increase in CdS QDs concentrations due to the Moss-Burstein effect. The enhanced values of the transparency, energy band gap and crystallity indicate that addition of CdS QDs can be used to modify the optical, structural and morphological properties of CdO thin films.Öğe Investigation of optical and device parameters of colloidal copper tungsten selenide ternary nanosheets(SPRINGER, 2018) Yildirim, Murat; Sarilmaz, Adem; Ozel, FarukHot injection synthesis route has been successfully applied for the preparation of high quality Cu2WSe4 (CWSe) nanosheets in order to determine their optical characterization and device parameters. Several techniques including XRD, SEM, TEM and SAED were used to characterize these nanosheets. These techniques confirmed that Cu2WSe4 nanosheets crystal shapes of synthesized are rectangular and square sheet and the average crystal size is between 20 and 40 nm. The spin coating technique was successfully used to deposit uniform of Cu2WSe4 thin film. Cu2WSe4 thin film has directly transition with a band gap of 1.64 eV. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple-Didomenico (WD) model. The single oscillator energy and the dispersion energy were estimated. Au/Cu2WSe4/n-Si structures was fabricated and its main electrical characteristics described by using current-voltage (I-V) methods. The forward and reverse bias current voltage (I-V) characteristics of Au/Cu2WSe4/n-Si at room temperature were studied to investigate its basic electrical parameters [i.e. saturation current (), ideality factor (), barrier height (), series ()]. Structural and optical mechanisms were discussed for future applications in optoelectronic devices.Öğe Investigation of optical framework of chalcostibite nanocrystal thin films: An insight into refractive index dispersion, optical band gap and single-oscillator parameters(ELSEVIER SCIENCE SA, 2017) Yildirim, Murat; Aljabour, Abdalaziz; Sarilmaz, Adem; Ozel, FarukHerein, we report the synthesis of chalcostibite ( CuSbS2) nanocrystals based on hot injection method and the characterization of CuSbS2 thin films by spin coating technique. The deposited films were subjected to the UV-Vis spectrophotometer, XRD, TEM and SAED for optical, structural, morphological and elemental analysis. XRD pattern showed that CuSbS2 nanocrystals have chalcostibite structures and SAED diffraction spots supported the XRD results. Different optical parameters like extinction coefficient, refractive index, real and imaginary parts of dielectric constant and surface and volume energy loss functions have been calculated applying single term Sellmeier dispersion relation and Wemple eDiDomenico single oscillator model. The obtained results are discussed in detail. The optical dispersion and dielectric properties of the CuSbS2 have been determined by the transmittance and reflectance modes in the range of 300-1600 nm. Thus, the CuSbS2 is transparent up to 40-45% in the visible range. The optical bandgap determined by the optical absorbance spectrum analysis showed that thin films possess direct bandgap of 1.86 eV. The calculated refractive index of thin film varies between 1.76 and 2.11 throughout the spectral region considered. The results presented here permit a better understanding of the properties of the chalcostibite nanocrystals which in turn result in the design of more efficient solar cells. (C) 2017 Elsevier B. V. All rights reserved.Öğe Investigation of structural, optical and dielectrical properties of Cu2WS4 thin film(SPRINGER, 2017) Yildirim, Murat; Ozel, Faruk; Sarilmaz, Adem; Aljabour, Abdalaziz; Patir, Imren HatayTernary I-Cu2WS4 were synthesized based on hot-injection process and their thin films are prepared by spin coating techniques at ambient temperature. The energy dispersive analysis of X-rays of the thin films confirmed that synthesized thin film is stoichiometric. Transmittance and reflectance have been used to determine the optical, dispersion and dielectric properties of the Cu2WS4 in the range of 200-2400 nm. The transparency of the Cu2WS4 is 40-45% in the visible range. Optical dispersion parameters have been calculated by using the single term Sellmeier dispersion relation and Wemple-DiDomenico single oscillator model. Several dispersion parameters were determined by the analysis of refractive index dispersion.Absorption coefficient (alpha), extinction coefficient (), the Urbach energy (), real and imaginary parts of dielectric constant (epsilon) and surface and volume energy loss function have been calculated. The optical bandgap determined by the optical absorbance spectrum analysis showed that thin films possess a direct bandgap of 1.74 eV.Öğe LUMINESCENCE ENHANCEMENT OF OLED PERFORMANCE BY DOPING COLLOIDAL MAGNETIC Fe3O4 NANOPARTICLES(EMW PUBLISHING, 2013) Kus, Mahmut; Ozel, Faruk; Varal, Nurhan M.; Ersoz, MustafaWe report synthesis of magnetic Fe3O4 nanoparticles (MNPs) based on two phase method and their application in organic light-emitting devices (OLEDs) as blend with emissive Polyfluorene (PFO) matrix. Two phase method allows to successively synthesizing oleic acid capped MPNs with 5-10 nm particle size. Colloidal MNPs can be easily mixed with emissive polymer solutions to obtain a blend for OLED application. The electroluminescence efficiency increases by doping with MNPs into emissive layer. Different dopant concentrations varied from 0,4% to 2% were monitored. It was observed that the electroluminescence increases up to 1% w/v doping ratio. The luminance of OLEDs increased from 15.000 cd/m(2) to 24.000 cd/m(2) in comparison pristine device with 1% MNP doped device.Öğe Magnetite nanoparticles: Synthesis, thin film properties and inkjet printing of magnetic cores for inductor applications(ELSEVIER SCIENCE SA, 2014) Marjanovic, Nenad; Chiolerio, Alessandro; Kus, Mahmut; Ozel, Faruk; Tilki, Serhad; Ivanovic, Nenad; Rakocevic, ZlatkoMagnetic thin films of preferred thickness, patterns, and characteristics were produced using digital printing at room temperature and under ambient conditions to realize magnetic cores for Radio Frequency Identification resonators. The magnetite nanoparticles (Fe3O4) covered with oleic acid were synthesized for that purpose and inkjet printed from chlorobenzene solution on flexible polyimide (PI) substrate and on paper. The obtained nanoparticles have a homogenous morphology, approximately round shape and a size distribution of 7-10 nm. The crystallite size in the films remains the same as in the powder, although aggregation takes place to various extents in the films providing different magnetic properties in each of them. The inkjet printed magnetic cores were investigated in the frequency range from 10 kHz to 11 MHz. Only the magnetic cores printed on PI and annealed at 300 degrees C for 1 h and 2 h exhibit ferromagnetism (mu(r) > 1) at low frequencies, and at higher frequencies all films saturate to mu(r) < 1. For the 300 degrees C-2 h annealed films the mu(r) saturation value is distinctly lower than for other films. mu(r) of the core realized on paper is lower than unity in the entire investigated range of frequencies and very uniform, especially at high frequencies. The presented results put forward the possibility of exploitation of the inkjet printed thin magnetic films in well-established manufacturing industries, such as the watch making, banknote watermarking, and the smart tag production. (C) 2014 Elsevier B.V. All rights reserved.Öğe Mechanical properties of zirconia after different surface treatments and repeated firings(KOREAN ACAD PROSTHODONTICS, 2014) Subasi, Meryem Gulce; Demir, Necla; Kara, Ozlem; Ozturk, A. Nilgun; Ozel, FarukPURPOSE. This study investigated the influence of surface conditioning procedures and repeated firings on monoclinic content and strength of zirconia before cementation. MATERIALS AND METHODS. Sintered bar-shaped zirconia specimens were subjected to no surface treatment (control), air abrasion, Or grinding (n=21). Their roughness was evaluated using a profilometer, and microscope analysis was performed on one specimen of each group. Then, 2 or 10 repeated firings (n=10) were executed, the monoclinic content of specimens was analyzed by X-ray diffraction, and a three-point flexural strength test was performed. Surface roughness values were compared using one-way analysis of variance (ANOVA) and Tukey honestly significant difference (HSD) tests, the monoclinic content values were tested using Kruskal-Wallis and Mahn-Whitney U tests, and the flexural strength values were tested using two-way ANOVA and Tukey HSD tests (P=.05). Spearman's correlation test was performed to define relationships among measured parameters. RESULTS. Surface-treated specimens were rougher than untreated specimens and had a higher monoclinic content (P<.005), and the relationship between roughness and monoclinic content was significant (P<.000). Neither surface treatment nor firing significantly affected the flexural strength, but Weibull analysis showed that for the air-abraded samples the characteristic strength was significantly. lower after the 10th firing than after. the 2nd firing. CONCLUSION. After firing, a negligible amount of monoclinic content remained on the zirconia surfaces, and rougher surfaces had higher monoclinic contents than untreated surfaces. Multiple firings Could be performed if necessary, but the fracture probability could increase after multiple firings for rougher surfaces.Öğe Nanofibrous cobalt oxide for electrocatalysis of CO2 reduction to carbon monoxide and formate in an acetonitrile-water electrolyte solution(ELSEVIER SCIENCE BV, 2018) Aljabour, Abdalaziz; Coskun, Halime; Apaydin, Dogukan Hazar; Ozel, Faruk; Hassel, Achim Walter; Stadler, Philipp; Sariciftci, Niyazi SerdarThe electrocatalytic reduction of carbon dioxide (CO2) is an attractive option to efficiently bind electrical energy from renewable resources in artificial carbon fuels and feedstocks. The strategy is considered as crucial part in closing the anthropogenic carbon cycle. In particular, the electrosynthetic production of Cl species such as carbon monoxide (CO) would radiate immense power, since these building blocks offer a versatile chemistry to higher carbon products and fuels. In the present study we report the exploration of the catalytic behavior of semiconducting Co3O4 nanofibers for the conversion of CO2 to CO predominantly with a Faradaic efficiency of 65%. We assist the process by expanding the electrode network with nanofibrous interconnections and hence are able to demonstrate the electrosynthesis of CO without applying any metal supplement. We use polyacrylnitrile (PAN) as template polymer to generate highly crystalline Co3O4 fibers to expand the catalytically active surface to volume ratio. The stability of the nanofibrous electrodes remains for 8 h at a geometric current density of approximately 0.5 mA/cm(2) on a flat surface. The ease of synthesis and the comparatively high Faradaic yield for CO makes Co3O4 nanofibers a potential candidate for future large scale electrode utilization.Öğe Penternary chalcogenides nanocrystals as catalytic materials for efficient counter electrodes in dye-synthesized solar cells(NATURE PUBLISHING GROUP, 2016) Ozel, Faruk; Sarilmaz, Adem; Istanbullu, Bilal; Aljabour, Abdalaziz; Kus, Mahmut; Sonmezoglu, SavasThe penternary chalcogenides Cu2CoSn(SeS)(4) and Cu2ZnSn(SeS)(4) were successfully synthesized by hot-injection method, and employed as a catalytic materials for efficient counter electrodes in dye-synthesized solar cells (DSSCs). The structural, compositional, morphological and optical properties of these pentenary semiconductors were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS) and ultraviolet-visible (UV-Vis) spectroscopy. The Cu2CoSn(SeS)(4) and Cu2ZnSn(SeS)(4) nanocrystals had a single crystalline, kesterite phase, adequate stoichiometric ratio, 18-25 nm particle sizes which are forming nanospheres, and band gap energy of 1.18 and 1.45 eV, respectively. Furthermore, the electrochemical impedance spectroscopy and cyclic voltammograms indicated that Cu2CoSn(SeS)(4) nanocrystals as counter electrodes exhibited better electrocatalytic activity for the reduction of iodine/iodide electrolyte than that of Cu2ZnSn(SeS)(4) nanocrystals and conventional platinum (Pt). The photovoltaic results demonstrated that DSSC with a Cu2CoSn(SeS)(4) nanocrystals-based counter electrode achieved the best efficiency of 6.47%, which is higher than the same photoanode employing a Cu2ZnSn(SeS)(4) nanocrystals (3.18%) and Pt (5.41%) counter electrodes. These promising results highlight the potential application of penternary chalcogen Cu2CoSn(SeS)(4) nanocrystals in low-cost, high-efficiency, Pt-free DSSCs.Öğe Photocatalytic H-2 evolution with a Cu2WS4 catalyst on a metal free D-pi-A organic dye-sensitized TiO2(ELSEVIER SCIENCE BV, 2017) Aslan, Emre; Gonce, Mehmet Kerem; Yigit, Mesude Zeliha; Sarilmaz, Adem; Stathatos, Elias; Ozel, Faruk; Can, MustafaA system comprising of a noble metal free Cu2WS4 catalyst and donor-pi-bridge-acceptor metal-free organic dyes (MZ-341 and MZ-235) sensitized TiO2 has been reported for the photocatalytic hydrogen production using triethanolamine (TEOA) as the sacrificial reagent under visible light irradiation. Cu2WS4 nanocubes were synthesized according to hot-injection reaction technique. The structural properties of the Cu2WS4 nanocubes were examined by microscopy (HR-TEM) and XRD techniques where the formation of nanocubes (rectangular and square cubes) with average edge length to be ranged from 100 to 500 nm and tetragonal phase (I-42m) was proved respectively. It was found that MZ-341 and MZ-235 dyes sensitized TiO2 have been produced 661 mol g 1 h(-1) and 531 mol g(-1) h(-1) hydrogen, respectively in TEOA solution at pH 9. When Cu2WS4, was used as a co-catalyst, hydrogen evolution by MZ-341 and MZ-235 sensitized TiO2 have been slightly increased to 1406 mol g(-1) h(-1) and 943 mol g(-1) h(-1), respectively. (C) 2017 Elsevier B.V. All rights reserved.
