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Author: search.filters.author.Pecharapa, WisanuSubject: search.filters.subject.Perovskite

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    Sonochemical Synthesis, Characterization, and Photocatalytic Activity of Perovskite ZnTiO3 Nanopowders
    (2016-10-01)
    Wattanawikkam, Chakkaphan
    ;
    Pecharapa, Wisanu
    Perovskite zinc titanate (ZnTiO<inf>3</inf>) nanopowders were synthesized using the sonochemical method combined with calcinations at 500 °C and 900 °C for 2 h to improve their crystallinity. The effect of calcination temperature on their structural, optical, and photocatalytic properties has been studied. The cubic phase and the mixing phase of cubic and hexagonal were observed in sample calcined at 600 °C and 700 °C, respectively, while the spinel ZnTiO<inf>3</inf> and rutile TiO<inf>2</inf> phase arises in sample calcined over 700 °C. The valence state was investigated by the X-ray absorption near-edge spectroscopy technique, and the corresponding results indicate the existence of Zn<sup>2+</sup> and Ti<sup>4+</sup> in the powders. The chemical states of the samples were scrutinized by X-ray photoelectron spectroscopy. The average particle size is approximately 20-240 nm. The excellent photocatalytic performance of ZnTiO<inf>3</inf> nanoparticle calcined at 700 °C gave complete degradation Rhodamine B (RhB) in 75 min under ultraviolet light exposure with the k rate of 0.033 min<sup>-1</sup> and 55% of decolorization RhB in 210 min under visible irradiation. The sample calcined at 700 °C ensures a good dielectric permittivity with a value 20 and the loss tangent of about 10<sup>-2</sup>.
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    Synchrotron X-ray absorption spectroscopy study of the local atomic structures and cation ordering in perovskite- and spinel-type zinc stannate synthesized by co-precipitation method
    (2015-12-15)
    Tangcharoen, Thanit
    ;
    Kongmark, Chanapa
    ;
    Pecharapa, Wisanu
    Zinc stannate nanocrystalline powders with two different crystal structures were synthesized from two different initial Zn<sup>2+</sup>/Sn<sup>4+</sup> ratios by a simple co-precipitation method. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) techniques were used to investigate crystal structure, oxidation, and cation ordering of the after-calcined powders. XRD patterns clearly showed that the ZnSnO<inf>3</inf> perovskite phase was obtained using an equal initial Zn<sup>2+</sup>/Sn<sup>4+</sup> ratio of 1:1, while a double Zn<sup>2+</sup> excess sample (2:1) produced the pure Zn<inf>2</inf>SnO<inf>4</inf> spinel phase. The chemical shifts in Zn K- and Sn L3-edge XANES spectra supported that only Zn<sup>2+</sup> and Sn<sup>4+</sup> ions existed in these stannate samples. Moreover, the theoretical simulation of the Zn K-edge EXAFS experimental data also indicated a change in the cation ordering from orthorhombic, for perovskite ZnSnO<inf>3</inf>, to cubic for spinel Zn<inf>2</inf>SnO<inf>4</inf>. This is the first time that the local atomic structural characterization of zinc stannate powders derived from EXAFS analysis has been presented.