Synthesis and Characterization of Single-Crystalline MnFe2O4 Ferrite Nanocrystals and Their Possible Application in Water Treatment

Manganese ferrite (MnFe2O4) nanospheres and nano-octahedra with a narrow size distribution were synthesized by a simple solvothermal method. Here, potassium permanganate (KMnO4) was used as reactant and oxidant for the synthesis of MnFe2O4 ferrite nanocrystals. With the use of hydrazine hydrate, the oxidation rate of ferrous ions was kept under control, and the particle size of MnFe2O4 was limited. The results of control experiments reveal that alkalinity and type of solvent are important factors affecting the morphology and crystallization of MnFe2O4 nanocrystals. Both of the as-prepared samples exhibit ferromagnetic behavior at room temperature. Especially, the saturation magnetization of MnFe2O4 nanospheres with 50 nm diameter is 79 emu/g, which is among the best values reported so far. The nanoparticles also showed good performance in removal of pollutants like Congo red, Cr-VI, and Pb-II from water by adsorption, even at neutral pH.