Abstract
Well-defined Mn3O4 powders have been prepared by an efficient method at room temperature. The routes include precipitation and oxidation of nano-crystalline Mn(OH)2 particles in the alkaline solution containing CO32- and excess OH- anions. For Mn3O4 synthesized by this process, particle sizes and morphology are sensitive to the preparation conditions, such as supersaturation level, pH value in the solution, and electrolytic concentration. The XRD patterns reveal that all products are in pure form and the crystallinity would be improved with increasing [CO32-] concentration. On the basis of the laser scattering data and SEM images, the average particle sizes range from 54 to 640 nm and become larger with increasing [Mn2+]initial and decreasing [OH-]excess . While the reagent concentrations were adjusted to certain values, the crystal shape tended to be more rounded. However, a few adsorbed CO32- ions on the crystal surface would result in the stacking fault of the assembling species and eventually the rounded fragments depart from the larger particles.During the process, particle size and morphology of derived products were totally different from the precursors even though nanometer-sized Mn(OH)2 crystals were fabricated at first. It was observed that the variation was resulted from the accumulation of produced Mn3O4 crystallites which departed from the original crystals. This study has not only confirmed the morphological transformation of crystals involved in autoxidation with the aid of electron micrographs, but also derived a feasible method to achieve uniform nanoparticles of Mn3O4.