Room temperature synthesis of a novel γ-MnO2 hollow structure for aerobic oxidation of benzyl alcohol

A novel gamma-MnO2 hollow structure has been synthesized at room temperature using a simple chemical reaction between MnSO4 and KMnO4 in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. The synthesized gamma-MnO2 hollow structure was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and BET analysis. It was found that the hollow structure consisting of short gamma-MnO2 nanorods with diameters of 5-10 nm and lengths of 50-100 nm could form when the MnSO4/KMnO4 mole ratio was equal to or larger than 2.3. The excess amount of Mn2+ in solution was observed to promote the crystallization of gamma-MnO2 nanorods and the formation of the gamma-MnO2 hollow structure. In addition, the evolution of microstructure and morphology of the products obtained with a MnSO4/KMnO4 mole ratio of 2.3 at different reaction times revealed that the hollow structure was formed via an Ostward ripening process. Furthermore, the obtained gamma-MnO2 hollow structure was found to exhibit a better catalytic performance than conventional gamma-MnO2 in the aerobic oxidation of benzyl alcohol to benzaldehyde, demonstrating its possible application in alcohol oxidation.