Preparation and characterization of uniform pseudocubic hematite particles by utilizing polyethylene oxide polymers in forced hydrolysis reaction

Abstract

The monodispersity of pseudocubic hematite particles, produced from a forced hydrolysis reaction of acidic FeCl 3 solution, were controlled by using five kinds of polyethylene oxides (PEO; Alkox μ ; Mesei Chemical Works. Ltd.) (02 wt.%). Alkox μ possesses nominal formula of (CH 2 CH 2 O) n . The fairly uniform pseudocubic particles was precipitated for PEO with low M w value and narrow molecular weight distribution. However, POEs with large molecular weight and wide molecular weight distribution produced polydispersed pseudocubic hematite particles. The PEO with the largest molecular weight attained nearly spherical with large particle size distribution. From the calculation of crystallite size, all the pseudocubic hematite particles were regarded as a polycrystal as well as the large spherical hematite particles produced without Alkox μ (control system). This polycrystallinity of the particles provided an evidence that the particles are grown by aggregation of polynuclear (PN) primary particles. The specific surface areas of the particles (SSA) were ranged in 410 m 2 /g and no large difference can be recognized among five kinds of PEOs. Since the measured SSA values were corresponded to the SSA one calculated by assuming monodispersed cubic particle with 300 nm in edge length, the pseudocubic hematite particles are non-porous. The time resolved XRD, TEM, ICP-AES and TOC measurements employed on the systems produced for pseudocubic particles elucidated that the pseudocubic crystal habit was formed by the specific adsorption of PEO molecules together with chloride ions and/or chloro ferric complexes to the {012} faces, restraining the growth process through stacking of ultrafine PN particles in the direction of normal to the {012} faces but strictly restricting the growth and mutual fusion of PN ones. The uniform pesudocubic particles found to be effective photocatalytic material than spherical and/or polydispersed pseudocubic hematite ones due to their large size with uniform flat crystal faces.