The impact of K+ content on the structural transformations and morphological changes during the thermal treatment of α-MnO2 nanorods

The effect of heat treatment on the structure and morphology of α-MnO2 nanorods with different potassium contents was investigated. These nanorods, prepared by ion exchange, were thermally treated at 500, 800, 1000 and 1100 °C, and characterized with X-ray diffraction and electron microscopy. The structure and morphology of the starting sample remained preserved up to 500 °C. The first structural and morphological changes were observed when α-MnO2 nanorods with different potassium contents were heated at 800 °C. The sample with the highest potassium content decomposed only partially to α-Mn2O3, while the decomposition of the α-MnO2 to α-Mn2O3 was complete in the sample with the lowest potassium content. Morphologically, both samples were composed of nanorods and grains. When the temperature was increased to 1000 and 1100 °C, both the structure and morphology changed: the α-MnO2 nanorods completely decomposed to Mn3O4 grains. The acidic media in which the ion exchange took place shortened the α-MnO2 nanorods.

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► The acidic treatment considerably shortened the α-MnO2 nanorods.
► α-MnO2 nanorods with higher potassium contents undergo to the structural changes at higher temperatures.
► Up to 500 °C no structural and morpholigcal changes are observed.