Effect of magnetic field on phase and morphology transformation of MnO2 nanostructures in a hydrothermal process

MnO2 nanostructures with various phases and morphologies were successfully synthesized by a magneticfield-assisted hydrothermal approach. By applying a pulsed magnetic field to the reaction system, the phase and morphology transformation progress, i.e. urchin-like alpha- and gamma-MnO2 nanostructures converting to beta-MnO2 nanowires was interfered comparing with those reacted without magnetic field. The effect of pulsed magnetic field on the growth of MnO2 was investigated by tracking the evolution of phase and morphology of the samples at different reaction stages by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. It is found that the pulsed magnetic field obviously affects the nucleation and growth of MnO2 nanostructures and therefore influences the phase and morphology transformation of MnO2. The transformation mechanism for the MnO2 nanostructures in hydrothermal treatment is the well-known "Ostwald ripening process". (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim