Synthesis and characterization of manganese dioxide spontaneously coated on carbon nanotubes

Manganese dioxide (MnO2) was coated on carbon nanotubes (CNTs) by simple immersion of the CNTs into a KMnO4 aqueous solution. The synthesis mechanism was investigated by in situ monitoring of the reduction potential and pH of the solution and supplementary UV-VIS analysis of MnO4- ions in the solution. CNTs were found to act as a reducing agent and substrate for the heterogeneous nucleation of MnO2 in an aqueous KMnO4 solution. The morphology of the CNTs before and after MnO2 deposition was examined using scanning electron microscopy, which showed MnO2 deposited as a thin and uniform layer on the CNTs at an initial pH of 7, but as nano-rods of MnO2 at an initial pH 1. The MnO2 was shown to be a Birnessite-type MnO2 by X-ray powder diffraction and Raman spectroscopy. The thermal stability of the CNTs, examined by thermogravimetric analysis, was improved by the thin, uniform and continuous coating of MnO2. (c) 2006 Elsevier Ltd. All rights reserved.