Solvothermal synthesis, characterization and magnetic properties of α-Fe2O3 and Fe3O4 flower-like hollow microspheres

The flower-like hollow microspheres of α-Fe2O3 and Fe3O4 have been prepared by a solvothermal combined with heat treatment method. A solvothermal method is adopted to synthesize flower-like hollow microspheres of the ferrous alkoxide precursor. N,N′-methylenebisacrylamide and CH3COONa play important roles in the formation of the flower-like hollow microspheres of the ferrous alkoxide precursor. The powder of flower-like hollow microspheres of ferrous alkoxide precursor can be transformed to flower-like hollow microspheres of α-Fe2O3 and Fe3O4 by heat treatment at 400 °C for 1 h in air and flowing nitrogen gas, respectively. During the heat treatment process, the morphology and size of the precursor can be preserved. The growth mechanism of the precursor is studied by time-dependent experiments, and the results show that the Ostwald ripening is responsible for the formation of hollow microspheres. α-Fe2O3 hollow microspheres exhibit a high coercivity value of 2738 Oe, and Fe3O4 hollow microspheres have a saturation magnetization of 58.3 emu g−1.