Magnetic greigite (Fe3S4) nanomaterials: Shape-controlled solvothermal synthesis and their calcination conversion into hematite (α-Fe2O3) nanomaterials

We demonstrated here the solvothermal synthetic method to selectively prepare magnetic greigite (Fe3S4) nanosheets and nanoparticles in the mixed solvents of ethylene glycol (EG) and H2O. The as-prepared Fe3S4 nanomaterials were further converted into hematite (α-Fe2O3) having branched structures under calcining conditions. The samples were well characterized by means of XRPD, FESEM, TEM, HRTEM, TGA and magnetic hysteresis curves. The experimental results reveal that the reaction parameters including the composition of mixed solvents, solvothermal temperature, and calcination temperature play important roles on achieving pure phase Fe3S4 and α-Fe2O3 samples. Significantly, we for the first time studied the elevated-temperature oxidation behavior of Fe3S4 sample into α-Fe2O3 in air, accompanying with the size and shape changing dramatically. The magnetic hysteresis curves of Fe3S4 show the ferromagnetic behaviors at room temperature.