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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

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

Tada Shotaro S Saito Shota S Mori Akito A Mizuno Hideki H Ando Shiori S Asaka Toru T Daiko Yusuke Y Honda Sawao S Bernard Samuel S Iwamoto Yuji Y

Materials (Basel, Switzerland) 20201125 23

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 ...[more]

PMID: 33255789

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Project description:Our studies of amorphous calcium phosphate (ACP)-based materials over the last decade have yielded bioactive polymeric composites capable of protecting teeth from demineralization or even regenerating lost tooth mineral. The anti-cariogenic/re-mineralizing potential of these ACP composites originates from their propensity, when exposed to the oral environment, to release in a sustained manner sufficient levels of mineral-forming calcium and phosphate ions to promote formation of stable apatitic tooth mineral. However, the less than optimal ACP filler/resin matrix cohesion, excessive polymerization shrinkage and water sorption of these experimental materials can adversely affect their physicochemical and mechanical properties, and, ultimately, limit their lifespan. This study demonstrates the effects of chemical structure and composition of the methacrylate monomers used to form the matrix phase of composites on degree of vinyl conversion (DVC) and water sorption of both copolymers and composites and the release of mineral ions from the composites. Modification of ACP surface via introducing cations and/or polymers ab initio during filler synthesis failed to yield mechanically improved composites. However, moderate improvement in composite's mechanical stability without compromising its remineralization potential was achieved by silanization and/or milling of ACP filler. Using ethoxylated bisphenol A dimethacrylate or urethane dimethacrylate as base monomers and adding moderate amounts of hydrophilic 2-hydroxyethyl methacrylate or its isomer ethyl-α-hydroxymethacrylate appears to be a promising route to maximize the remineralizing ability of the filler while maintaining high DVC. Exploration of the structure/composition/property relationships of ACP fillers and polymer matrices is complex but essential for achieving a better understanding of the fundamental mechanisms that govern dissolution/re-precipitation of bioactive ACP fillers, and, ultimately, the suitability of the composites for clinical evaluation.

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

Publications

Reversible Redox Property of Co(III) in Amorphous Co-doped SiO<sub>2</sub>/γ-Al<sub>2</sub>O<sub>3</sub> Layered Composites.

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Dataset Information

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

Publications

Reversible Redox Property of Co(III) in Amorphous Co-doped SiO<sub>2</sub>/γ-Al<sub>2</sub>O<sub>3</sub> Layered Composites.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

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