Synthesis and Redox Properties of Iron and Iron Oxide Nanoparticles Obtained by Exsolution from Perovskite Ferrites Promoted by Auxiliary Reactions

Abstract

Nanoparticles of iron and iron oxides, as well as their composites, are of great scientific and technological interest. However, their properties and sustainability strongly depend on the preparation methods. Here, we present an original approach to synthesizing Fe and FeNix metal nanoparticles by exsolution, in a reducing environment at elevated temperatures from perovskite ferrites (La1−xCaxFeO3−γ, CaFeO2.5, etc.). This approach is made possible by the auxiliary reactions of non-reducible A-site cations (in ABO3 notation) with the constituents of reducing compounds (h-BN etc.). The nanoparticles exsolved by our process are embedded in oxide matrices in individual voids formed in situ. They readily undergo redox cycling at moderate temperatures, while maintaining their localization. Fe nanoparticles can be obtained initially and after redox cycling in the high-temperature γ-form at temperatures below equilibrium. Using their redox properties, a new route to producing hollow and layered oxide magnetic nanoparticles (Fe3O4, Fe3O4/La1−xCaxFeO3−γ), by separating the oxidized exsolved particles, was developed. Our approach provides greater flexibility in controlling exsolution reactions and matrix compositions, with a variety of possible starting compounds and exsolution degrees, from minimal up to ~100% (in some cases). The described strategy is highly important for the development of a wide range of new functional materials.

Keywords

• transition metal-embedded nanoparticles
• metal exsolution
• ⁵⁷Fe Mössbauer spectroscopy
• redox behavior
• hollow and layered oxide nanoparticles
• cup-shaped nanoparticles