Controlled synthesis of hierarchical MnO2 microspheres with hollow interiors for the removal of benzene

Abstract

Three types of MnO₂ microspheres, viz., hierarchical hollow β-MnO₂ microspheres consisting of uniform nanorods, hierarchical double-walled hollow β/α-MnO₂ microspheres assembled by two-categorical nanorods, and hierarchical hollow α-MnO₂ microspheres constructed by nanorods and nanowires, have been synthesized by a facile hydrothermal method without employing any templates, catalysts, surfactants or calcinations. A number of characterization techniques, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), nitrogen adsorption–desorption measurements, and X-ray photoelectron spectroscopy (XPS) are used to characterize the formed hierarchical products, and to address the following critical issues: (i) effect of the precursor concentration; (ii) the role of HCl for the formation of the hierarchical hollow structure; and (iii) the possible mechanism accounting for the formation of the hierarchical hollow microspheres. The hierarchical hollow MnO₂ microspheres can be used as catalysts for the catalytic oxidation of benzene, of which the hierarchical hollow α-MnO₂ microspheres exhibit the highest catalytic ability.