Structural and morphological control of manganese oxide nanoparticles upon soft aqueous precipitation through MnO4−/Mn2+ reaction

A low-temperature (60 or 95 °C) “one-pot” procedure for the aqueous precipitation of manganese oxide nanoparticles is developed through the MnO4−/Mn2+ reaction. Characterization of the particles is carried out using elemental analysis, mean oxidation state determination, powder XRD, FESEM, TEM and electron diffraction. Many synthesis parameters are investigated, such as acidity, reactant ratio, concentration and nature of the counter-cation, temperature and aging time. Speciation diagrams are drawn for the synthesis of five different pure phases (spinel-type Mn3O4, layered birnessite-type δ-MnO2, tunnel-based frameworks cryptomelane-type α-MnO2, γ-MnO2 and pyrolusite β-MnO2). The influence of synthetic parameters is rationalized and reaction pathways toward various structures and morphologies are discussed.