A top-down synthetic method was developed for the fabrication of sponge-like Mn3O4 composed of Mn3O4 nanocrystals by decomposition of manganese formate at 200 °C. The samples were characterized in terms of their structural and morphological properties by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) studies. TEM and SEM images showed that the morphology of sponge-like Mn3O4 structures was mostly retained from the morphology of the manganese formate precursor, which was controlled by the solvothermal process. Large sponge-like Mn3O4 structures exhibiting crystallographic symmetry were prepared under solvothermal treatment for a long time. The XRD pattern showed that the Mn3O4 exhibit a tetragonal hausmannite structure. The results of N2 adsorption analysis indicated that the sponge-like Mn3O4 nanostructures possess high surface area. The possible formation mechanism of Mn3O4 nanostructures has been discussed.
