Porous α-Fe₂O₃ nanostructures with branched topology: Growth, formation mechanism, and properties

Porous hematite (α-Fe₂O₃) with branched nanostructures such as V and Y shapes were prepared through dehydration of goethite (α-FeOOH) precursor, while α-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 α-Fe₂O ₃ 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)° 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 α-Fe₂O₃. The as-prepared α-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.