Formation of Hollow and Porous Nanostructures of Iron Oxides via Oxidation of Iron Nanoparticles and Nanowires

Changes in morphology during the oxidation of iron nanoparticles and nanowires at 473~ 873 K have been studied by transmission electron microscopy. Iron nanoparticles and wires become hollow nanoparticles and nanotubes of Fe3O4 at temperatures below 673 K as a result of vacancy aggregation in the oxidation process. On the other hand, the hollow magnetite transforms into duplex porous structures with an interior nanopore and additional nanovoids at higher temperatures above 673 K, where the shrinkage of hollow nanoparticles and nanotubes starts and the phase transformation from Fe3O4 to -Fe2O3 occurs. Transition in porous structure seems to be related to the outward diffusion of vacancies from interior pore and the phase transformation in the shrinkage process.