Magnetic greigite (Fe_3S_4) nanomaterials: Shape-controlled solvothermal synthesis and their calcination conversion into hematite (alpha-Fe_2O_3) nanomaterials

摘要

We demonstrated here the solvothermal synthetic method to selectively prepare magnetic greigite (Fe_3S_4) nanosheets and nanoparticles in the mixed solvents of ethylene glycol (EG) and H_2O. The as-prepared Fe_3S_4 nanomaterials were further converted into hematite (alpha-Fe_2O_3) 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 Fe_3S_4 and alpha-Fe_2O_3 samples. Significantly, we for the first time studied the elevated-temperature oxidation behavior of Fe_3S_4 sample into alpha-Fe_2O_3 in air, accompanying with the size and shape changing dramatically. The magnetic hysteresis curves of Fe_3S_4 show the ferromagnetic behaviors at room temperature.