Capping Groups Induced Size and Shape Evolution of Magnetite Particles Under Hydrothermal Condition and their Magnetic Properties

Three simple capping molecules (urea, 3-aminopropanol, and polyethylene glycol) with different functional groups (−NH₂ for urea, −NH₂ and −OH for 3-aminopropanol, and −O− for polyethylene glycol) have been designed to prepare magnetite (Fe₃O₄) particles with various shapes. The crystal structure, morphologies, and magnetic properties of the products have been characterized by X-ray diffraction, electron microscopy, and vibrating sample magnetometer. The results indicate that the capping functional groups play a major role in determining the size, shape, and thus magnetic properties of the magnetite nanocrystals. The morphology evolution of the magnetite under the hydrothermal condition is discussed in detail, particularly for the interaction between the various capping groups and surface structure and chemistry of the nanocrystals.