Synthesis of various magnetite nanoparticles through the simple phase transformation and their shape-dependent magnetic properties

Abstract

Shape-controlled synthesis of iron oxide nanoparticles had been successfully carried out through the simple phase transformation via polyol process using akaganeite (β-FeOOH) as a single precursor material. Different shapes of iron oxide nanoparticles including solid spheres, solid rods, and hollow rods could be obtained by either adding appropriate amount of sodium acetate (NaOAc) or the anion exchange of β-FeOOH. The possible mechanism for formation of Fe3O4 with different shapes was proposed. The NaOAc could make it possible to retain the rod shape of precursor materials (β-FeOOH) during the phase transformation by coordinating the surface and controlling basic pH to slow down dissolution-recrystallization mechanism. We also proposed that chloride ions in β-FeOOH structure play a key role in the formation of hollow structure. The shape-dependent magnetic properties were investigated with magnetic property measurement system at 300K. All iron oxide nanoparticles exhibited ferromagnetic behavior with different value of saturation magnetization (Ms) and coercivity (Hc) which highly depended on the shape of the nanoparticles due to their different grain size, spin disorder, shape and surface anisotropy. It would be systematic studies of shape-dependent magnetic properties, especially for comparison between hollow rods and solid rods, because of their comparable structural size and average grain size and negligible effect of other parameters such as surfactant that could affect crystallinity and crystal defects of nanoparticles.