Synthesis and Surface Characterization of γ-MnO2 Nanostructures

A facile method was developed to synthesize gamma-MnO2 with different structures and surface properties in this paper. gamma-MnO2 was prepared by oxidation of MnSO4 with Na2S2O8 at 90 degrees C for 2.0h. gamma-MnO2 formed at initial pH 1.0 (M1) and 8.5 (M2) was composed of MnO1.93 center dot 0.23H(2)O and MnO1.96 center dot 0.18H(2)O, respectively. The higher ratio of pyrolusite in M2 (P-r = 43.90%) than that in M1 (P-r = 24.86%) indicated that compared with M1, M2 would absorb more protons since the planar oxygen atoms in pyrolusite were incompletely coordinated and liable to absorb the protons. Meanwhile, the higher oxidation valence of Mn in M2 than that in M1 revealed that the Mn atoms in M2 were more liable to draw the electron density from the surface oxygen atoms in hydroxyl groups. The structural and compositional differences between M1 and M2 were the major reasons why M2 possessed a higher surface potential and a weaker ability to absorb Zn2+ ions.