A closer look at the synthesis and formation mechanism of hematite nanocubes

We have synthesized hematite cube-shaped nanoparticles using different synthesis paths to examine the effect of the intermediate product akaganeite (β-FeOOH) on the size and shape of the final hematite particles. Akaganeite spindles and hematite nanocubes are prepared using forced hydrolysis of iron chloride (FeCl3) salt. We use a combination of transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) and dynamic light scattering (DLS). Akaganeite particles are found to be spindles, with an average length that depends linearly on the FeCl3 concentration, while their aspect ratio is hardly affected by the same parameter. Adjusting the akaganeite concentration from 0.01 M to 0.10 M equivalent of FeCl3 in the subsequent transformation to hematite leads to single crystal nanocubes with sizes ranging from 37 to 175 nm. The combination of akaganeite concentration and size is found to be the key parameter to control the size and crystallinity of the resulting hematite particles. Possible formation mechanisms of single and polycrystalline hematite nanocubes are discussed.