Controlled synthesis of Mn3O4 and MnCO3 in a solvothermal system

Controlled synthesis of Mn3O4 nanocrystals and MnCO3 aggregates was achieved by a facile solvothermal method using different divalent manganese source in the solvent of N,N-dimethylformamide (DMF) with/without the introduction of poly(vinylpyrrolidone) (PVP). PVP was used as a co-reducing reagent in the controlled formation of MnCO3 crystal. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED), Fourier transform infrared (FTIR) spectra, Raman spectrum and magnetic measurement. Higher process temperature and longer solvothermal time were favorable for the formation of MnCO3 single phase using MnCl2 as the manganese source. Mn3O4 nanocrystals were prepared at a relatively lower temperature. MnCO3 aggregates consisted by small nanoparticles have a certain orientation, showing that the nanocrystals formed earlier through oriented aggregation. The size of Mn3O4 nanocrystals was 22.5 ± 7.3 nm and 7.3 ± 1.4 nm prepared using MnCl2 and Mn(CH3COO)2, respectively, at 160 °C for 24 h. Raman spectra showed size-dependent characteristics. Smaller Mn3O4 nanoparticle resulted in a red-shift in Raman spectra. Magnetic property of the prepared Mn3O4 nanoparticle was influenced by the size distribution and crystallinity.