Nonstoichiometric Zn Ferrite and ZnFe 2 O 4 /Fe 2 O 3 Composite Spheres: Preparation, Magnetic Properties, and Chromium Removal

Monodisperse and porous nonstoichiometric Zn ferrite can be prepared by a solvothermal method. Such non-Zn ferrite was used to be the precursor for synthesis of ZnFe 2 O 4 /Fe 2 O 3 composite via calcination at 600°C for 3 h in air. X-ray powder diffractometer (XRD) and Energy Dispersive Spectrometer (EDS) proved the nonstoichiometry of Zn ferrite synthesized by solvothermal method and the formation of ZnFe 2 O 4 /Fe 2 O 3 composite via calcination. TEM image showed that non-Zn ferrite spheres with wormlike nanopore structure were made of primary nanocrystals. BET surface area of non-Zn ferrite was much higher than that of ZnFe 2 O 4 /Fe 2 O 3 composite. Saturation magnetization of non-Zn ferrites was significantly higher than that of ZnFe 2 O 4 /Fe 2 O 3 composites. Calcination of non-Zn ferrite resulted in the formation of large amount of non-magnetic Fe 2 O 3 ,which caused a low magnetization of composite. Because of higher BET surface area and higher saturation magnetization, non-Zn ferrite presented better Cr 6+ adsorption property than ZnFe 2 O 4 /Fe 2 O 3 composites.