Iron(III) oxide nanoparticles occur in several phases, particularly α-Fe₂O₃ (hematite) and γ-Fe₂O₃ (maghemite), each with distinct magnetic and electronic properties. At the nanoscale, they exhibit high surface activity and stable dispersion in aqueous systems. They are used as pigments, in catalytic and photocatalytic reactions such as solar water splitting, and in magnetic adsorbents for environmental remediation.