Self-assembly of single-crystalline α-Fe2O3 nanoplates into columnar superstructures: controllable synthesis, growth mechanism, and properties

Self-assembly of crystalline alpha-Fe2O3 nanoplates into columnar one dimensional superstructures (CODS) was achieved in high yield by a simple hydrothermal route in the presence of glycerin. The alpha-Fe2O3 micro-/nanocrystals with controllable sizes and morphologies, such as nanospheres, nanoparticles, polyhedrons and plates, were also synthesized by this facile process. Contrast experiments indicated that the glycerin not only acted as a structure-directing agent for controlling growth of alpha-Fe2O3 plates but also played a role in assembling alpha-Fe2O3 individual plates into columnar superstructures. Based on the time-dependent experiments, a reasonable growth mechanism of alpha-Fe2O3 CODS has been proposed. The obtained alpha-Fe2O3 crystals displayed ferromagnetic behavior and their magnetic properties were dependent on their sizes and shapes. Furthermore, the coercivity values of the alpha-Fe2O3 single microplates (similar to 2.5 mu m in diameter) and CODS (similar to 2.2 mu m in length) were high up to 1872.6 Oe and 889.7 Oe, respectively. In addition, gas sensors based on plate-like alpha-Fe2O3 and their CODS exhibited high sensitivity for ethanol and formaldehyde, respectively.