Porous alpha-Fe2O3 nanostructures with branched topology: growth, formation mechanism, and properties

Porous hematite (alpha-Fe2O3) with branched nanostructures such as V and Y shapes were prepared through dehydration of goethite (alpha-FeOOH) precursor, while alpha-FeOOH branched nanostructures are self-organized by straight nanorods via facet-mediated oriented attachment mechanism at high pH without the use of organic additives. This novel approach is different from the mechanisms reported for other alpha-Fe2O3 anisotropic structures. Based on combined TEM, high-resolution TEM and AFM analyses, a possible formation mechanism of branched nanostructures was suggested. A V-shaped rod with a dihedral angle of (118.0 +/- 4.0)degrees is connected by two straight needle-shaped rods sharing comparable three dimensions; the subsequent merger of a V-shaped rod with a straight rod leads to a Y-shaped rod. This is the first demonstration of branched topology with single-domain crystallinity for alpha-Fe2O3. The as-prepared alpha-Fe2O3 nanostructures displays two Morin transition temperatures at 195 and 243 K. The results from the current study could provide potential implications in self-and directed-engineering shape anisotropy with unique and useful magnetic and other properties through the oriented attachment mechanism.