Size Control Synthesis of Uniform β-FeOOH to High Coercive Field Porous Magnetic α-Fe2O3 Nanorods

Abstract

Uniform β-FeOOH (akaganeite) nanorods with different sizes featuring highly ordered channel-type nanoporous structures were synthesized by simple reproducible one-step hydrothermal method without surfactant and size selection processes. Systematic control of the aspect ratio and mean size of the β-FeOOH nanorods was achieved by regulating the concentration of hydrochloric acid. The length and diameter of these rods could be varied from 270 to 650 nm and from 32 to 21 nm, respectively. It is seen that the size of the β-FeOOH rods strongly depends upon the chloride ion concentration and also upon other added foreign inorganic salt and base. In particular, the β-FeOOH nanorods synthesized with small diameter less than 10 nm are reported for the first time here. The nanorod formation mechanism was proposed on the basis of the evolution of the structure and the morphology, along with variation of the ion concentration. The resulting rod-shaped iron hydroxides were transformed into porous α-Fe2O3 nanorods by slow heating at 250 °C for 2 h. The magnetic properties measured by superconducting quantum interference device technique revealed that the α-Fe2O3 nanorods displayed ferromagnetic behavior. High coercive value up to 1.46 T, which is the largest, reported so far is observed for these α-Fe2O3 magnetic nanorods.