Nano-micro-architectural composites with acid properties: Magnetic iron oxides/amorphous silicate prepared from iron oxide produced by iron-oxidizing bacterium, Leptothrix ochracea

摘要

To develop novel magnetic composites with acid functionalities, iron oxide produced by iron-oxidizing bacterium, Leptothrix ochracea, was used as a precursor. The composites were prepared by thermal treatment and subsequent reduction of the bacterial iron oxide. a-Fe_2O_3 nanoparticles obtained in air were thermally reduced to Fe3O4 and gradually oxidized to 7-Fe_2O_3. The obtained composites with Fe_3O_4 and γ-Fe_2O_3 have high magnetization values that are approximately half those of pure Fe_3O_4 and γ-Fe_2O_3. All samples have an interesting nano-micro-architectural structure: ～40-nm-diameter crystalline particles covered with ～8-nm-thick amorphous silicate are intricately interconnected into ～1 -μ-m-diameter microtubules. Pyridine adsorption spectra indicate that the surface amorphous silicate has both Bronsted and Lewis acid properties.