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

ABSTRACT: This paper reports on a unique reversible reducing and oxidizing (redox) property of Co(III) in Co-doped amorphous SiO₂/?-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 ?-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/?-Al₂O₃ hetero interface, and the redox reactions were governed by the H₂ partial pressure at 250-500 °C. As a result, a supported mesoporous ?-Al₂O₃/Co-doped amorphous SiO₂/mesoporous ?-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.

SUBMITTER: Tada S 

PROVIDER: S-EPMC7728299 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature