Facile route to control the surface morphologies of 3D hierarchical MnO2 and its Al self-doping phenomenon

In this article, a catalytic-ion assisted hydrothermal method has recently been developed for synthesis of hierarchical manganese dioxide nanostructures. In this study, various shapes of hierarchical MnO2 (nanorod, nanothorn sphere, sphere) were successfully synthesized using the hydrothermal method with quantitative control of Al3+ in solution. The aspect ratio of aligned nanorods on the nanothorn sphere was easily controlled by the amount of Al3+ in the MnSO4 and (NH4)(2)S2O8 aqueous solution. Furthermore, we found that Al3+ species in the solution acted as a functional doping species into 2 x 2 tunnels of alpha-MnO2 and also as a catalyst. The formation mechanism of hierarchical MnO2 structures as a function of Al3+ concentration during hydrothermal reaction was sufficiently investigated, and the role of Al3+ as catalyst and doping species in the solution was discussed.