Microstructural characterizations of different Mn-oxide nanoparticles used as models in toxicity studies

Mn-oxide microstructures were investigated by XRD, FT-IR, TEM, FE SEM and EDS techniques. The oxidation of the aqueous solutions of manganese (II) chloride by hydrogen peroxide was employed to synthesize pure 20–30-nm pseudospherical hausmannite (Mn3O4) nanoparticles and manganite (γ-MnOOH) nanowires. The α-MnO2 nanotubes and nanorods were hydrothermally synthesized starting from a KMnO4 precursor, then modified with the addition of divalent metal cations Mn2+, Cu2+, Ni2+ and Fe2+. The modification with Mn2+ induced the transformation of α-MnO2 nanotube into 3D β-MnO2 (pyrolusite) prismatic nanoparticles, whereas the low-crystalline α-MnO2 nanorods were transformed into disk-like γ-MnO2 nanoparticles. The modification with Cu2+ and Ni2+ induced the structural transformation of α-MnO2 into a mixture of MnO2 polymorphs. The modification with Cu2+ decreased, whereas the modification with Ni2+ improved the crystallinity of MnO2. The modification with Fe2+ induced the structural transformation of α-MnO2 into γ-MnO2, a decrease in crystallinity and the segregation of α-Fe2O3 (hematite). Thus the modification of MnO2 with Fe2+ (Mn2+) divalent metal cations that can be oxidized into Fe3+ (Mn4+) by a KMnO4 precursor differs significantly in comparison with, in this case, non-oxidizable cations such as Cu2+ and Ni2+. On the other hand, the advantage that the modification of MnO2 with Mn2+ produces chemically identical compounds with different morphology can be used as a model system for toxicity studies. In this work the preliminary measurements of intracellular oxidative stress in epithelial cells induced by manganese oxide nanoparticles are reported.

• The synthesis and properties of Mn3O4, γ-MnOOH and MnO2 nanoparticles of various morphologies were investigated.
• Influence of divalent metal cations on the crystal structure and morphology of MnO2 nanoparticles was shown.
• Possible use of Mn-oxide nanoparticles in toxicity studies is shown.