Nanocystals of Hematite with Unconventional Shape-Truncated Hexagonal Bipyramid and Its Optical and Magnetic Properties

The capping agent plays a critical function in anisotropic crystal growth to induce polyhedral morphology of a nanocrystal. Uniform and single-crystalline alpha-Fe2O3 polyhedral nanoparticles in the hexagonal single crystal system named truncated hexagonal bipyramid for the first time were successfully synthesized by a facile one-step hydrothermal method with the aid of carboxymethyl cellulose and hydrazine molecules. The appearance and crystal structure of these iron oxide nanopartides were characterized in detail by physicochemical methods. The results show that the as-synthesized alpha-Fe2O3 particles are bound by 12 same-side crystalline facets {101} and two other same facets {001} at the tops. These obtained iron oxide particles belong to a pure hematite phase, and the particle size is around 400 nm. The optical property of the assynthesized product was analyzed, and the determined indirect band gap value E-g is 2.08 eV. The magnetic property studies of truncated hexagonal bipyramid hematite particles have shown that this kind of alpha-Fe2O3 possess a weak ferromagnetism under the T-M, and the saturation points do not reach up to the maximum applied magnetic field. Role of the reactants was discussed and investigated systematically in the work. Furthermore, a schematic illustration for the probable formation of this alpha-Fe2O3 morphology in whole of the synthetic process was also proposed.