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Perovskite Sr1−xBaxW1−yTay(O,N)3: synthesis by thermal ammonolysis and photocatalytic oxygen evolution under visible light

Kawashima, Kenta and Hojamberdiev, Mirabbos and Stabler, Christina and Vrankovic, Dragoljub and Yubuta, Kunio and Riedel, Ralf and Domen, Kazunari and Teshima, Katsuya (2017):
Perovskite Sr1−xBaxW1−yTay(O,N)3: synthesis by thermal ammonolysis and photocatalytic oxygen evolution under visible light.
In: Materials for Renewable and Sustainable Energy, Springer Berlin, Heidelberg, 6, (2), ISSN 2194-1459,
DOI: 10.1007/s40243-017-0094-4,
[Online-Edition: https://doi.org/10.1007/s40243-017-0094-4],
[Article]

Abstract

To study the effect of partial Ba2+-to-Sr2+ and/or Ta5+-to-W4–6+ substitution on various properties of SrW(O,N)3, cubic perovskite-type W- and/or Ta-based oxynitrides Sr1−x Ba x W1−y Ta y (O,N)3, where x,y = 0,0; 0.25,0; 0.125,0.125; 0,0.25; and 1.1, were synthesized by ammonolyzing their corresponding oxide precursors under an NH3 flow. The synthesized oxynitrides have highly porous structures and consist of small crystallites in the range of 53–630 nm and with specific surface areas in the range of 5.4–14.7 m2·g−1. Interestingly, the Ta5+-to-W4~6+ substitution in SrW(O,N)3 can suppress the formation of reduced tungsten species during thermal ammonolysis. The weaker absorptions beyond 560 and 580 nm in the UV–Vis diffuse reflectance spectra, which correspond to reduced tungsten species, are observed in SrW0.75Ta0.25(O,N)3 and Sr0.875Ba0.125W0.875Ta0.125(O,N)3 compared to SrW(O,N)3 and Sr0.75Ba0.25W(O,N)3. The XPS results reveal that low-valent transition metal oxides, nitrides, and oxynitrides and/or tungsten metal are present on the surfaces of the as-synthesized oxynitrides. After 5 h of the photocatalytic oxygen evolution reaction, CoO x -loaded SrW0.75Ta0.25(O,N)3 exhibited the highest amount of evolved O2 gas due to its higher specific surface area and lower concentration of intrinsic defects. During the photocatalytic reaction, the N2 gas is also evolved because of the self-oxidation of oxynitrides consuming photo-generated holes. The estimated TONs of the oxynitride samples exceeded one, evidencing that the observed O2 gas evolution reactions were catalytic. Accordingly, the photostability enhancement of oxynitrides reduces the loss of photo-generated charge carriers and increases their photocatalytic activity.

Item Type: Article
Erschienen: 2017
Creators: Kawashima, Kenta and Hojamberdiev, Mirabbos and Stabler, Christina and Vrankovic, Dragoljub and Yubuta, Kunio and Riedel, Ralf and Domen, Kazunari and Teshima, Katsuya
Title: Perovskite Sr1−xBaxW1−yTay(O,N)3: synthesis by thermal ammonolysis and photocatalytic oxygen evolution under visible light
Language: English
Abstract:

To study the effect of partial Ba2+-to-Sr2+ and/or Ta5+-to-W4–6+ substitution on various properties of SrW(O,N)3, cubic perovskite-type W- and/or Ta-based oxynitrides Sr1−x Ba x W1−y Ta y (O,N)3, where x,y = 0,0; 0.25,0; 0.125,0.125; 0,0.25; and 1.1, were synthesized by ammonolyzing their corresponding oxide precursors under an NH3 flow. The synthesized oxynitrides have highly porous structures and consist of small crystallites in the range of 53–630 nm and with specific surface areas in the range of 5.4–14.7 m2·g−1. Interestingly, the Ta5+-to-W4~6+ substitution in SrW(O,N)3 can suppress the formation of reduced tungsten species during thermal ammonolysis. The weaker absorptions beyond 560 and 580 nm in the UV–Vis diffuse reflectance spectra, which correspond to reduced tungsten species, are observed in SrW0.75Ta0.25(O,N)3 and Sr0.875Ba0.125W0.875Ta0.125(O,N)3 compared to SrW(O,N)3 and Sr0.75Ba0.25W(O,N)3. The XPS results reveal that low-valent transition metal oxides, nitrides, and oxynitrides and/or tungsten metal are present on the surfaces of the as-synthesized oxynitrides. After 5 h of the photocatalytic oxygen evolution reaction, CoO x -loaded SrW0.75Ta0.25(O,N)3 exhibited the highest amount of evolved O2 gas due to its higher specific surface area and lower concentration of intrinsic defects. During the photocatalytic reaction, the N2 gas is also evolved because of the self-oxidation of oxynitrides consuming photo-generated holes. The estimated TONs of the oxynitride samples exceeded one, evidencing that the observed O2 gas evolution reactions were catalytic. Accordingly, the photostability enhancement of oxynitrides reduces the loss of photo-generated charge carriers and increases their photocatalytic activity.

Journal or Publication Title: Materials for Renewable and Sustainable Energy
Volume: 6
Number: 2
Publisher: Springer Berlin, Heidelberg
Uncontrolled Keywords: Water oxidation, Oxynitride, perovskite, Visible light, Substitution
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Dispersive Solids
Date Deposited: 17 Jan 2018 11:29
DOI: 10.1007/s40243-017-0094-4
Official URL: https://doi.org/10.1007/s40243-017-0094-4
Funders: This research was supported in part by the Japan Technological Research Association of Artificial Photosynthetic Chemical Process (ARPChem).
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