Size-controlled synthesis of Fe₃O₄ and Fe₃O₄@SiO₂ nanoparticles and their superparamagnetic properties tailoring

Superparamagnetic properties and fine-tuning of colloidal Fe₃O₄ nanoparticles are important for their widespread biomedical applications. Herein, colloidal Fe₃O₄ nanoparticles (NPs) of different sizes (8–20 ​nm) were prepared, and their hydrophilization with SiO₂ shell coating to be Fe₃O₄@SiO₂ core-shell had been realized successively. The size of Fe₃O₄ NPs was controlled by different heating rates. Transmission electron microscope (TEM), powder X-ray diffractometry (XRD), and vibrating sample magnetometer (VSM) were performed to examine the morphology, crystallinity, and magnetic properties of the prepared Fe₃O₄ and Fe₃O₄@SiO₂ core-shell NPs, respectively. In addition, high resolution transmission electron microscope (HRTEM) results suggested that Fe₃O₄ NPs had well crystallization. Enabled by such, their superparamagnetic properties can be fine-tuned accordingly and cater to their potential applications.