Synthesis and surface characterization of γ -MnO2 nanostructures

Abstract

A facile method was developed to synthesize γ-MnO2 with different structures and surface properties in this paper. γ-MnO 2 was prepared by oxidation of MnSO4 with Na 2S2O8 at 90 ° C for 2.0 h. γ-MnO 2 formed at initial pH 1.0 (M1) and 8.5 (M2) was composed of Mn O 1.9 3 · 0.23 H2O and Mn O 1.9 6 · 0.18 H2O, 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. © 2013 Chengxiang Liu et al.