Simple Surfactant Concentration-Dependent Shape Control of Polyhedral Fe3 O4 Nanoparticles and Their Magnetic Properties.

The shape and size of monodisperse Fe3 O4 nanoparticles (NPs) are controlled using a chemical solution synthesis in the presence of the surfactant cetylpyridinium chloride (CPC). Cubic Fe3 O4 NPs surrounded by six {100} planes are obtained in the absence of CPC. Increasing the CPC content during synthesis causes the shape of the resulting Fe3 O4 NPs to change from cubic to truncated cubic, cuboctahedral, truncated octahedral, and finally octahedral. During this evolution, the predominantly exposed planes of the Fe3 O4 NPs vary from {100} to {111}. The shape control results from the synergistic effect of the pyridinium cations, chloride anions, and long-chain alkyl groups of CPC, which is confirmed by comparison with NPs synthesized in the presence of various related cationic surfactants. The size of the cubic Fe3 O4 NPs can be tuned from 50 to 200 nm, by changing the concentration of oleic acid in the reaction solution. The Fe3 O4 NPs exhibit shape-dependent saturation magnetization, remanent magnetization, and coercivity.