Growth Mechanism of Dendritic Hematite via Hydrolysis of Ferricyanide

The detailed process of the hydrolysis of ferricyanide into dendritic α-Fe2O3 (hematite) crystals with snowflake-like, feather-like, and leaf-like morphologies has been investigated. [Fe(CN)6]3– anions were found to polymerize into large, disordered soft matter aggregates at an early stage. The nucleation of hematite crystals took place near the surface of these aggregates via further hydrolysis. After the crystals grew to a certain size, branches started to appear. When the concentration of ferricyanide was low (i.e. 2 mM to 3.8 mM), growth was preferentially along the six equivalent ⟨1120⟩ directions, resulting in a flat snowflake-like shape, while high concentrations (i.e. 9 mM to 500 mM) of ferricyanide led to the growth of selective directions along the ⟨1011⟩ zone axes, forming a feather-like or leaf-like morphology. Highly selective adsorption and surface hydrolysis of [Fe(CN)6]3– anions on α-Fe2O3 crystals was found to be a crucial process in the formation of these novel morphologies. It was fou...