Synthesis of hexagonal and triangular Fe₃O₄ nanosheets via seed-mediated solvothermal growth

Hexagonal and triangular monodisperse Fe₃O₄ nanosheets have been synthesized via a two-step microemulsion solvothermal approach in which uniform Fe₃O₄ nanoparticles are first prepared and then these hydrophobic nanocrystals are dispersed in a uniform microemulsion environment as "seeds" for further re-growth through a secondary solvothermal process. The growth of anisotropic morphologies has been explained by the presence and orientation of twin planes in the face-centered cubic Fe₃O₄ which direct the shape of the growing particles. In particular, reentrant grooves resulting from twin planes are favorable sites for the addition of adatoms, leading to anisotropic growth. Triangular nanosheets are believed to contain one twin face which directs the growth of the primary particles in two dimensions. Hexagonal nanosheets are believed to contain two parallel planes that allow the growth edges to regenerate one another. The growth mechanism is evidenced by the analysis of high-resolution transmission electron microscopy (HRTEM) results and the as-prepared Fe₃O₄ nanoparticles have been shown to be an effective catalyst in the synthesis of quinoxaline.