Ammonium mediated hydrothermal synthesis of nanostructured hematite (α-Fe2O3) particles

Uniform α-Fe2O3 particles of different shapes have been synthesized through hydrothermal process. The additives, the type of Fe(III) salts and reaction conditions in hydrothermal process were thoroughly investigated. The crystalline structure and morphology of the as-synthesized powder have been characterized by using X-ray powder diffraction, scanning electron microscopy and field emission scanning electron microscopy. Rod and ellipsoidal-shaped α-Fe2O3 were obtained with ferric chloride as a precursor, while only irregular-shaped particles were synthesized by using ferric nitrate as precursors in the absence of NH4OH. Direct transformation of micro-rod hematite to ellipsoidal particles with FeCl3 as precursor was also observed by adding NH4OH. It is shown that the nanorod was formed through presumed directional aggregation of rapidly formed nucleus, while the formation of ellipsoidal hematite particles may undergo a nucleation–aggregation–dissolution–recrystallization process in the presence of ammonium.