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    Facile synthesis of cobalt-doped zinc oxide thin films for highly efficient visible light photocatalysts
    (ELSEVIER SCIENCE BV, 2016) Yildirim, Ozlem Altintas; Arslan, Hanife; Sonmezoglu, Savas
    Cobalt-doped zinc oxide (Co:ZnO) thin films with dopant contents ranging from 0 to 5 at.% were prepared using the sol-gel method, and their structural, morphological, optical, and photocatalytic properties were characterized. The effect of the dopant content on the photocatalytic properties of the films was investigated by examining the degradation behavior of methylene blue (MB) under visible light irradiation, and a detailed investigation of their photocatalytic activities was performed by determining the apparent quantum yields (AQYs). Co2+ ions were observed to be substitutionally incorporated into Zn2+ sites in the ZnO crystal, leading to lattice parameter constriction and band gap narrowing due to the photoinduced carriers produced under the visible light irradiation. Thus, the light absorption range of the Co:ZnO films was improved compared with that of the undoped ZnO film, and the Co:ZnO films exhibited highly efficient photocatalytic activity (similar to 92% decomposition of MB after 60-min visible light irradiation for the 3 at.% Co:ZnO film). The AQYs of the Co:ZnO films were greatly enhanced under visible light irradiation compared with that of the undoped ZnO thin film, demonstrating the effect of the Co doping level on the photocatalytic activity of the films. (C) 2016 Elsevier B.V. All rights reserved.
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    Room temperature synthesis of Cu incorporated ZnO nanoparticles with room temperature ferromagnetic activity: Structural, optical and magnetic characterization
    (ELSEVIER SCI LTD, 2016) Yildirim, Ozlem Altintas; Durucan, Caner
    Copper-incorporated zinc oxide (ZnO:Cu) nanoparticles with different amounts of Cu incorporation (Cu:Zn ratio at% of 1.25, 2.5 and 5) were synthesized for the first time by a room temperature precipitation technique without any subsequent post thermal treatment. Pure ZnO nanoparticles were also synthesized for direct structural and property-related comparison purposes. ZnO:Cu nanoparticles were thoroughly characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy, vibrating sample magnetometer, UV-visible and photoluminescence spectroscopy. Detailed crystallographic investigation was accomplished through Rietveld refinement. ZnO:Cu nanoparticles exhibited room temperature ferromagnetic (RTFM) property. The origin of RTFM in ZnO:Cu nanoparticles has been investigated and this property was attributed to the substitutional incorporation of Cu ions into the ZnO lattice. The evidence for substitutional incorporation has been demonstrated with the positional changes in XRD peaks of ZnO and accompanying precise lattice parameter analyses by Rietveld refinement. Chemical analysis by XPS revealed incorporation of copper as Cu2+ ions. The Rietveld-based percent occupancy values for Zn sites imply certain limited substitution of the Cu2+ ions into the ZnO lattice with the increasing amount of Cu. Meanwhile, the magnetization enhanced with increasing Cu amount, due to the narrowing band gap, suggesting that RTFM characteristics are an intrinsic property of ZnO:Cu nanoparticles. This work gives insight into the origin of RTFM in ZnO nanoparticles and can be used to enhance ferromagnetism in diluted magnetic semiconductors. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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    Synthesis of uniformly distributed single- and double-sided zinc oxide (ZnO) nanocombs
    (ELSEVIER SCIENCE BV, 2015) Yildirim, Ozlem Altintas; Liu, Yuzi; Petford-Long, Amanda K.
    Uniformly distributed single- and double-sided zinc oxide (ZnO) nanocomb structures have been prepared by a vapor-liquid-solid technique from a mixture of ZnO nanoparticles and graphene nanoplatelets. The ZnO seed nanoparticles were synthesized via a simple precipitation method. The structure of the ZnO nanocombs could easily be controlled by tuning the carrier-gas flow rate during growth. Higher flow rate resulted in the formation of uniformly-distributed single-sided comb structures with nanonail-shaped teeth, as a result of the self-catalysis effect of the catalytically active Zn-terminated polar (0001) surface. Lower gas flow rate was favorable for production of double-sided comb structures with the two sets of teeth at an angle of similar to 110 degrees to each other along the comb ribbon, which was attributed to the formation of a bicrystal nanocomb ribbon. The formation of such a double-sided structure with nanonail-shaped teeth has not previously been reported. (C) 2015 Elsevier B.V. All rights reserved,