Hydrothermal Synthesis of Octadecahedral Hematite (α-Fe2O3) Nanoparticles: An Epitaxial Growth from Goethite (α-FeOOH)

• Published in: Journal of physical chemistry. C 2014-05, Vol.118 (20), p.10903-10910
• Main Authors: Lin, Ming, Tng, Liling, Lim, Tongyi, Choo, Meeling, Zhang, Jia, Tan, Hui Ru, Bai, Shiqiang
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp502087h

Driven by the demand for shape-controlled synthesis of α-Fe2O3 nanostructures and the understanding of their growth mechanism and shape-dependent properties, we report the synthesis of octadecahedral α-Fe2O3 nanocrystals with a hexagonal bipyramid shape by introducing F– anions in the solution. The hydrothermal growth process from hydrolysis of Fe3+ precursors involves three steps: the nucleation of akaganeite (β-FeOOH) nanorods, followed by the formation of goethite (α-FeOOH) crystals with acicular and twinned shapes, and a subsequent transformation into hematite (α-Fe2O3) nanoparticles. The phase transformation and growth of α-Fe2O3 particles from α-FeOOH follows dissolution of goethite and reprecipitation as hematite process. The initial nucleation of α-Fe2O3 particles was found to form epitaxially on goethite {001} surfaces due to a perfect lattice match between goethite {001} surface and hematite {001} planes. The structural relationship between goethite and hematite is G(020)//H(030) with G[100]//H[100]. The obtained α-Fe2O3 hexagonal bipyramid particles are enclosed by 12 {113} planes and six {104} facets. Since the twinned α-FeOOH particles are one of the typical shapes of intermediate goethite crystals, the nucleation of hematite particles on two twinned arms gives rise to the formation of twinned hematite particles. F– anions play an important role in the formation of α-Fe2O3 particles with a hexagonal bipyramid shape because high concentration of F– anions can stabilize the exposed {113} surfaces. The controlled synthesis of α-Fe2O3 nanoparticles with defined surfaces not only provides significant information on hematite surface structures and energies but also is critical to give the structure–property relationship for the application of hematite materials.