Single crystal manganese oxide hexagonal plates with regulated mesoporous structures

Porous hexagonal plates of manganese oxides are prepared by a simple hydrothermal method from metal Mn foils/powders and manganese acetate precursors under basic conditions. The oriented aggregation-based assembly of the nanoparticles of mixed feitknechtite and hausmannite phases gave rise to well-defined hexagonal nanoplates with irregular mesopores of ∼5 nm in size. The hexagonal plate-like morphology was retained after calcination, and mesoporous single-crystalline Mn5O8 and α-Mn2O3 plates were obtained after calcinations at 400 and 700 °C, respectively. The interior mesopores in each plate were enlarged with the increase of calcination temperature, and turned out to be regular-shaped, i.e. polyhedral or even well-defined rectangular. Furthermore, 700 °C -calcination led to the fusion of nanocrystals into structurally uniform α-Mn2O3 crystals of hexagonal plates with regular-shaped mesoporous structure. X-ray diffraction and electron diffraction, scanning and transmission electron microscopy, X-ray energy dispersive spectroscopy, and nitrogen sorption analysis were employed to characterize these porous nanoplates. Such mesoporous hexagonal nanoplates of manganese oxides with high crystallinity may have many applications.