Preparation of echinoid-like aggregated hematite particles by forced hydrolysis with PEO-PPO-PEO triblock copolymers

Sub-micrometre sized hematite particles with a controlled structure were prepared by forced hydrolysis of a Fe(NO3)3·9H2O aqueous solution in the presence of poly(alkylene oxide) triblock copolymer (Pluronic P123). The resulting particles show an echinoid-like shape and a narrow size distribution. After removal of the polymer by calcination at 500 C for 3 h, the resulting particles show a retained size and shape with disordered mesopores. Calcination also leaded to the complete transformation of crystallinity from ferric oxyhydroxide to hematite. Forced hydrolysis of the ferric ion solution in the presence of poly(ethylene oxide) (PEG) and poly(N-vinyl-2-pyrrolidone) (PVP) was also carried out to investigate the mechanism of the particle formation. Particles which resulted from PEG and PVP solutions have a different shape or a randomly aggregated form. The formation of micelles of Pluronic P123 copolymer and the hydrogen bonding between the exterior of micelles and inorganic precursors are responsible for the isotropic shape of particles.