Fabrication of gamma-MnO2/alpha-MnO2 hollow core/shell structures and their application to water treatment

In this work, we present a novel concept of structural design for the synthesis of a new type of core/shell structure comprising gamma-MnO2 cores inside hollow alpha-MnO2 shells. The approach involves two main steps. First, MnCO3 microellipsoids were mixed directly with KMnO4 solution, which lead to a manganese oxide shell on the surface of the MnCO3. Then, thermal annealing of this type of core/shell structure resulted in the formation of gamma-MnO2/alpha-MnO2 ellipsoids, accompanying with the phase transition in both the core and shell. The as-prepared gamma-MnO2/alpha-MnO2 ellipsoids were used as adsorbent in water treatment, and showed an excellent ability to remove organic pollutants and heavy metal ions without any other additives.