Continuous Shape- and Spectroscopy-Tuning of Hematite Nanocrystals

Abstract

Uniform hexagonal hematite (α-Fe₂O₃) nanoplates have been synthesized by a facile alcohol-thermal reaction, and a new nanostructure of α-Fe₂O₃ has been proposed. Each nanoplate is enclosed by (0001) basal planes and {101̅2} side surfaces. The phase, size, shape, and growth orientation of these nanocrystals were characterized by powder X-ray diffraction and electron microscopy. The thickness and diameter of these nanocrystals could be finely tuned by the selective use of alcohol solvent with increasing carbon atom number in the linear alkyl chain. A variety of nanocrystals with systemically changeable shapes from nanoplates to nanograins have been obtained. Specific adsorption of alcohol molecules on polar (0001) facets is proposed to be the main issue to modify the growth behavior of hematite nanocrystals. The presence of distilled water and the addition of sodium acetate have also been investigated. Either of them has a great influence on the growth of hematite nanocrystals, and shape-controlled growth can be rationally achieved. In addition, the post-aging of as-grown hematite nanocrystals in alcohol and distilled water has also been described. Both vibration spectroscopy (i.e., FTIR and Raman) and electronic spectra (diffused reflectance spectra) of these nanocrystals with a continuing shape change show a highly shape-dependent nature.