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Open AccessArticle

Reversible Redox Property of Co(III) in Amorphous Co-doped SiO2/γ-Al2O3 Layered Composites

1
Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
2
Centre Européen de la Céramique, University of Limoges, 12 Rue Atlantis, 87068 Limoges, France
*
Author to whom correspondence should be addressed.
Materials 2020, 13(23), 5345; https://doi.org/10.3390/ma13235345
Received: 29 October 2020 / Revised: 17 November 2020 / Accepted: 23 November 2020 / Published: 25 November 2020
(This article belongs to the Section Materials Chemistry)
This paper reports on a unique reversible reducing and oxidizing (redox) property of Co(III) in Co-doped amorphous SiO2/γ-Al2O3 composites. The Fenton reaction during the H2O2-catalyzed sol–gel synthesis utilized in this study lead to the partial formation of Co(III) in addition to Co(II) within the composites. High-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analyses for the composite powder sample with a composition of Al:Si:Co = 85:10:5 showed the amorphous state of the Co-doped SiO2 that modified γ-Al2O3 nanocrystalline surfaces. In situ X-ray absorption fine structure (XAFS) spectroscopic analysis suggested reversible redox reactions of Co species in the composite powder sample during heat-treatment under H2 at 500 °C followed by subsequent cooling to RT under Ar. Further analyses by in situ IR spectroscopy combined with cyclic temperature programmed reduction/desorption (TPR/TPD) measurements and X-ray photoelectron spectroscopic (XPS) analysis revealed that the alternating Co(III)/(II) redox reactions were associated with OH formation (hydrogenation)-deformation (dehydrogenation) of the amorphous aluminosilicate matrix formed in situ at the SiO2/γ-Al2O3 hetero interface, and the redox reactions were governed by the H2 partial pressure at 250–500 °C. As a result, a supported mesoporous γ-Al2O3/Co-doped amorphous SiO2/mesoporous γ-Al2O3 three-layered composite membrane exhibited an H2-triggered chemical valve property: mesopores under H2 flow (open) and micropores under He flow (closure) at 300–500 °C. View Full-Text
Keywords: Co(III); aluminosilicate; reversible Co(III)/(II) redox property; membrane; H2-triggered chemical valve property Co(III); aluminosilicate; reversible Co(III)/(II) redox property; membrane; H2-triggered chemical valve property
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MDPI and ACS Style

Tada, S.; Saito, S.; Mori, A.; Mizuno, H.; Ando, S.; Asaka, T.; Daiko, Y.; Honda, S.; Bernard, S.; Iwamoto, Y. Reversible Redox Property of Co(III) in Amorphous Co-doped SiO2/γ-Al2O3 Layered Composites. Materials 2020, 13, 5345. https://doi.org/10.3390/ma13235345

AMA Style

Tada S, Saito S, Mori A, Mizuno H, Ando S, Asaka T, Daiko Y, Honda S, Bernard S, Iwamoto Y. Reversible Redox Property of Co(III) in Amorphous Co-doped SiO2/γ-Al2O3 Layered Composites. Materials. 2020; 13(23):5345. https://doi.org/10.3390/ma13235345

Chicago/Turabian Style

Tada, Shotaro; Saito, Shota; Mori, Akito; Mizuno, Hideki; Ando, Shiori; Asaka, Toru; Daiko, Yusuke; Honda, Sawao; Bernard, Samuel; Iwamoto, Yuji. 2020. "Reversible Redox Property of Co(III) in Amorphous Co-doped SiO2/γ-Al2O3 Layered Composites" Materials 13, no. 23: 5345. https://doi.org/10.3390/ma13235345

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