The effect of heat treatment on the structure and morphology of alpha-MnO2 nanorods with different potassium contents was investigated. These nanorods, prepared by ion exchange, were thermally treated at 500, 800, 1000 and 1100 degrees C, and characterized with X-ray diffraction and electron microscopy. The structure and morphology of the starting sample remained preserved up to 500 degrees C. The first structural and morphological changes were observed when alpha-MnO2 nanorods with different potassium contents were heated at 800 degrees C. The sample with the highest potassium content decomposed only partially to alpha-Mn2O3, while the decomposition of the alpha-MnO2 to alpha-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 degrees C, both the structure and morphology changed: the alpha-MnO2 nanorods completely decomposed to Mn3O4 grains. The acidic media in which the ion exchange took place shortened the alpha-MnO2 nanorods. (C) 2012 Elsevier Ltd. All rights reserved.