Synthesis of Mn3O4 nanoparticles via a facile gel formation route and study of their phase and structural transformation with distinct surface morphology upon heat treatment

Mn3O4 nanoparticles (NPs) were synthesized from the reduction of KMnO4 with glycerol at 80 °C in aqueous media via a gel formation route. In order to investigate the thermal stability and phase transformation, Mn3O4 NPs were subjected to heat treatment from 200 °C to 700 °C. The formation of different MnOx species observed by X-ray diffraction (XRD) measurements showed temperature dependent phase transformation occurring during the heat treatment process. XRD patterns showed that Mn3O4 NPs were formed at a temperature of 80 °C and two new phases Mn5O8 and Mn2O3 were appeared at 350 °C and 700 °C respectively. The three different oxides having their distinct surface morphologies viz., spherical, rod and cube shape respectively, were observed. Detailed morphological and structural investigations using Field Emission Scanning Electron Microscopy (FESEM), XRD, Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) revealed the temperature dependent phases, crystal structures, lattice constants, particle sizes and surface morphologies of the MnOx species.