pH value-dependant growth of α-Fe2O3 hierarchical nanostructures

The controllable synthesis of two kinds of α-Fe2O3 hierarchical nanostructures, i.e., three-dimentional (3D) houseleek-like and two-dimentional (2D) snowflake-like dendrites were achieved through a simple hydrothermal route by changing pH value. The growth of α-Fe2O3 dendrites was proceeded by self-assembly through two different modes of oriented attachment (OA): when pH⩽6, primary α-Fe2O3 nanoparticles attached preferentially along the six crystallographically equivalent 〈11¯00〉 directions, resulting in the formation of sixfold-symmetric dendrites. While at pH⩽5, the growth process involved two steps: firstly, primary nanoparticles aggregated to form round flakes with their up and bottom surfaces parallel to {0 0 0 1} plane. These flakes stacked face-to-face with each other along [0 0 0 1] direction to construct the single crystalline spindle-like α-Fe2O3, which then aggregated together at the tips to construct the 3D houseleek-like dendrites. As far as we know, this is the first time using different modes of OA to realize the morphology control of hierarchical structures in one reaction system.