Hydrothermal synthesis, characterization, and growth mechanism of hematite nanoparticles

Polyhedron-shaped hematite (α-Fe₂O₃) nanoparticles have been successfully synthesized via a facile hydrothermal method by mixing FeCl₃ and NH₄OH at high temperature. In this work, the influences of experimental conditions such as the effects of the concentration of iron's ion, NH4OH concentration, and reaction temperature on the hematite's particle size, dispersity, and growth rate were investigated. Results show that hematite nanoparticles with good crystallinity with the particle size of 100 nm could be obtained when the hydrothermal reaction was carried out with concentration of Fe³⁺ = 16 mM, NH₄OH = 40 mM, reaction temperature = 120 °C, and reaction time = 24 h. In addition, this study investigates the hematite nanoparticle-formation mechanism with reaction time. It is observed that the formation of hematite nanoparticles are initiated by the formation of intermediate phase of goethite nanorods in the early stage of hydrothermal reaction, which further transform into hematite crystal as the reaction is progressed.