Tunable Synthesis of Hierarchical Superparamagnetic Fe3O4 Nanospheres by a Surfactant-Free Solvothermal Method

Hierarchical Fe3O4 nanospheres with superparamagnetism have been fabricated via a solvothermal method without any surfactants. The effect of reaction parameters like the types of the reagent, the reaction time, and the reagent concentration on the morphology and structure of the resultant samples are investigated. In this method, ferric chloride (FeCl3 ⋅ 6H2O) is used as the iron source, and EG acts as both solvent and reducing agent. The presence of NaHCO3 or Na2CO3 provides alkine condition and gaseous bubbles in the control over the size of Fe3O4 nanospheres. The formation mechanism for Fe3O4 nanospheres is illustrated by an Ostwald ripening process. The Fe3O4 nanospheres were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and superconducting quantum interference device magnetometer (SQUID-VSM). The Fe3O4 nanospheres exhibited a wider size distribution at the amount of 0.397 mol/L NaHCO3, showing a high saturation magnetization close to 84.46 emu/g. The Fe3O4 nanospheres soluble in deionized water is also investigated.