Facile synthesis, shape evolution and magnetic properties of polyhedral 50-facet Fe3O4 nanocrystals partially enclosed by {311} high-index planes

Abstract

Magnetite (Fe₃O₄) polyhedral nanocrystals have been prepared successfully by a simple solvothermal reaction using a mixture of ethylene glycol (EG) and H₂O as the solvent without the addition of any surfactants or templates. Based on SEM and TEM characterization, the products were determined to be 50-facet Fe₃O₄ nanocrystals, 200–300 nm in diameter, enclosed by {100}, {110}, {111}, and high-index {311} facets. The morphological evolution of 50-facet Fe₃O₄ polyhedra was studied carefully and in detail by adjusting the reaction parameters such as the reaction temperature, the reaction time, the amount of urea, and the volume ratio of EG to H₂O in the solvent. The results indicated that an appropriate EG/H₂O ratio in the solvent was crucial for the formation of the polyhedral nanocrystals and when the solvent was fixed, the size of the polyhedral nanocrystals could be tuned in a certain range by changing the amount of urea. A possible growth mechanism involving the aggregation and oriented attachment of Fe₃O₄ seed nanoparticles is proposed on the basis of time-dependent experiments.