Transformation of Cryptomelane-Type Manganese Oxides to Oxygen Deficient Systems by Microwave-Induced Oxygen Evolution

Abstract

Cryptomelane, a one-dimensional tunnel manganese oxide, is a good microwave absorber due to the effective coupling of MnO2 with microwave irradiation. Transformations of cryptomelane were studied under microwave heating conditions at a frequency of 2.45 GHz. Microwave-induced oxygen evolution is fast and uniform, leading to the formation of oxygen deficient products. Microwave products in contrast to conventional heated products exhibited a strong tendency to adsorb water, and recombine with oxygen. The water adsorbed on the surface of materials is highly ordered. Oxygen recombination led to a recovery of the cryptomelane structure and a decrease in the level of the oxygen deficient phase. A reversible process during microwave-induced oxygen evolution and subsequent oxygen recombination is proposed.