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 tinder 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 similar to 5 nm in size. The hexagonal plate-like morphology was retained after calcination, and mesoporous single-crystalline Mn5O8 and alpha-Mn2O3 plates were obtained after calcinations at 400 and 700 degrees 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 degrees C-calcination led to the fusion of nanocrystals into structurally uniform alpha-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. (C) 2007 Elsevier Inc. All rights reserved.