Manganese oxide nanostructures: low-temperature selective synthesis and thermal conversion

Abstract

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.