Manganese oxide nanostructures: low-temperature selective synthesis and thermal conversion†
Nanostructured MnOx with crystalline phases of γ-MnOOH, δ-MnO2, α-Mn2O3, and Mn3O4 as well as rod, sheet, cube, and particle shapes were prepared via a facile, high-yield and low-temperature (60 °C) reduction route, without templates or surfactants. Selective preparation was achieved just by adjusting the amount of H2O2 or reactant concentration that controls simultaneously the growth thermodynamic and dynamic parameters of MnOx nanocrystals. Our results show that the bundle-like γ-MnOOH nanorods are formed through a lamellar growth, dissolution–recrystallization and oriented attachment process. Furthermore, the corresponding bundle-like β-MnO2, α-Mn2O3, and Mn3O4 nanorods were prepared by calcining these γ-MnOOH precursors under different atmospheres and temperatures. This synthetic procedure is simple, inexpensive and high-yield, and thus facilitates mass production of manganese oxide nanomaterials.