Preparation and characterization of disk-shaped hematite particles by a forced hydrolysis reaction in the presence of polyvinyl alcohol

The effect of polyvinyl alcohol (PVA) on the formation of spherical hematite particles from a forced hydrolysis reaction of acidic FeCl3 solution was examined. With increasing the PVA concentration, the shape of hematite particles was varied from spherical to disk-like by reducing their thickness. TEM and SEM observations clearly revealed that the disk-like hematite particles with average diameters of ca. 500 nm and aspect ratios of about 2 are consisting of aggregated cluster particles with a diameter of ca. 5–10 nm. The hematite particles formed with PVA were hydrohematite with a crystal lattice distortion and exhibited a polycrystalline nature. These particles changed from microporous to mesoporous after elimination of residual PVA molecules adsorbing on cluster particles by evacuating the samples above 300 °C. This result supports the fact that hematite particles produced by the forced hydrolysis reaction are aggregates, as we further revealed recently by using simultaneous temperature programmed desorption, mass spectroscopy and thermogravimetric measurements (Phys. Chem. Chem. Phys., 2001, 3, 2949). It was suggested that the large voids between the cluster particles filled with PVA molecules within the disk-like particles produce mesopores after eliminating the PVA molecules.