Size-controlled synthesis and magnetic properties of NiFe2O4 hollow nanospheres via a gel-assistant hydrothermal route

A facile gel-assistant hydrothermal procedure has been used to prepare spinel hollow nanospheres. NiFe2O4 hollow nanospheres with diameter in the range of 90–180 nm were successfully synthesized via direct hydrothermal decomposition of a gel of Ni–Fe–EG (EG = ethylene glycol) in water solution without adding any template or surfactant. The crystal structure, composition and morphologies of the products were characterized by XRD, ICP-AES, FTIR, XPS, SEM, TEM, and SAED. The results of XRD, ICP-AES, XPS and SAED show that the products were pure NiFe2O4. During the reaction process, reaction temperature and time have a significant effect on the final products. The formed NiFe2O4 nanospheres at 190 °C for 6 h have average diameters of ca. 90 nm with BET surface area of about 73.5 m2 g−1. Furthermore, all the obtained NiFe2O4 hollow nanospheres exhibit low saturation magnetization and high coercivity. Moreover, the possible formation mechanism was also discussed.