Decolorization of methylene blue in layered manganese oxide suspension with H2O2

Layered birnessite-type manganese oxides (Na-OL-1) were prepared via a redox reaction involving MnO4- and Mn2+ under markedly alkaline conditions. According to the XRD analysis, the resulting material exhibited a well-crystallized octahedral layer (OL) structure with several different phases, including beta-MnOOH, alpha-MnOOH and gamma-Mn3O4. The catalyst was highly effective for the decolorization and degradation of methylene blue (MB) in the presence of H2O2 at neutral pH. The tested MB was completely decolorized in Na-OL-1 suspension by the fraction dosing of H2O2 (556.5 mM at the beginning and then 183.8 mM at 40 min). Based on the studies of electron spin resonance and the effect of radical scavengers, the O-1(2) and O-2(center dot-) were the main reactive oxygen species (ROS) in the reaction. It was found that both oxygen and ROS were generated from the decomposition of H2O2 in Na-OL-1 suspension, wherein the decomposition pathways were proposed. The generation of H2O2 in Na-OL-1 suspension at air atmosphere indicated that the existence of multivalent manganese oxides greatly enhanced the interfacial electron transfer, leading to the high activity of Na-OL-1. (C) 2011 Published by Elsevier B.V.