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 degrees C for 6 h have average diameters of ca. 90 nm with BET surface area of about 73.5 m(2) g(-1). Furthermore, all the obtained NiFe2O4 hollow nanospheres exhibit low saturation magnetization and high coercivity. Moreover, the possible formation mechanism was also discussed. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.