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Structures, electron density and characterization of novel photocatalysts, (BaTaO2N)1−x(SrWO2N)x solid solutions

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Abstract

Tungsten-modified barium tantalum oxynitride is a new visible-light photocatalyst for water oxidation. In the present work, novel barium tantalum strontium tungsten oxynitride solid solutions, (BaTaO2N)1−x(SrWO2N)x, with a cubic Pm[3 with combining macron]m perovskite-type structure (x = 0.01 and 0.02) have been prepared by heating oxide precursors under an ammonia flow. These (BaTaO2N)1−x(SrWO2N)x catalysts exhibited photocatalytic water oxidation activity under visible light irradiation. The crystal structure, electron-density distribution, and optical properties of (BaTaO2N)1−x(SrWO2N)x (x = 0, 0.01, and 0.02) have been studied using synchrotron X-ray powder diffraction, Rietveld analysis, the maximum-entropy method (MEM), and UV-Vis reflectance measurements. The lattice parameters of (BaTaO2N)1−x(SrWO2N)x decreased linearly with increasing SrWO2N content x. The minimum electron density (MED) at the (Ta,W)–(O,N) bond, determined by the MEM analysis of (BaTaO2N)1−x(SrWO2N)x, increased with x, as supported by DFT-based calculations. These results indicate the formation of (BaTaO2N)1−x(SrWO2N)x solid solutions and enhanced covalent bonding due to the stronger W–N bond. The MED of the (Ta,W)–(O,N) bond was higher than that of (Ba,Sr)–(O,N), indicating that the (Ta,W)–(O,N) bond is more covalent. The presence of nitrogen in (BaTaO2N)1−x(SrWO2N)x was confirmed by the occupancy factor refined using neutron diffraction data and by the weight gain observed by thermogravimetric analysis in air. UV-Vis reflectance spectra and DFT calculations indicated that (BaTaO2N)1−x(SrWO2N)x contains W5+ cations with a [Xe] 4f14 5d1 electron configuration and exhibits a more n-type semiconducting character compared with BaTaO2N, which could improve the photocatalytic water oxidation activity under visible-light irradiation.

Graphical abstract: Structures, electron density and characterization of novel photocatalysts, (BaTaO2N)1−x(SrWO2N)x solid solutions

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Publication details

The article was received on 04 Aug 2017, accepted on 25 Sep 2017 and first published on 26 Sep 2017


Article type: Paper
DOI: 10.1039/C7DT02873C
Citation: Dalton Trans., 2017, Advance Article
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    Structures, electron density and characterization of novel photocatalysts, (BaTaO2N)1−x(SrWO2N)x solid solutions

    K. Hibino, M. Yashima, T. Oshima, K. Fujii and K. Maeda, Dalton Trans., 2017, Advance Article , DOI: 10.1039/C7DT02873C

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