The Tremendous Influence of Calcination Process on the Phase Structure and Catalytic Activity of Precipitation-Processed MnO2

Abstract

The layer and tunnel manganese oxides are versatile materials and have been proposed for various applications. These materials are prepared by a wide range of methods such as sol-gel, solid-state, precipitation and etc. Here, both manganese oxides of birnessite (layer) and cryptomelane (tunnel) have been successfully synthesized using the precipitation method by the reaction between KMnO4 and glucose with a mole ratio of 3:1. XRD results indicated that the birnessite-type manganese oxide was obtained when the brownish-black precipitate was heated up to 120°C, whereas cryptomelane-type manganese oxide was generated when the as-synthesized sample was further calcined up to 600°C. The birnessite sample displays poor crystalline material with low intensity and broad peak. The heat-treated birnessite up to 600°C leads to the formation much more crystalline tunnel cryptomelane–type mangane oxide. The catalytic activities of the as-synthesized catalysts were tested for the degradation of methylene blue (MB) dye with H2O2 as an oxidant. The birnessite catalyst shows much higher catalytic activity for the degradation of methylene blue compared to the cryptomelane catalyst. The tremendous improved catalytic activity of birnessite catalyst are correlated with its poor crystallinity and higher surface area of as indicated by the BET surface area and the XRD results.