The Cu-doped cryptomelane-type octahedral molecular sieve manganese oxide synthesized by sol-gel for the degradation of methylene blue

Abstract

The sol-gel method was used to prepare pure cryptomelane and Cu-doped cryptomelane octahedral molecular sieve manganese oxide materials using CuSO4·5H2O as the dopant source. The one-step synthetic approach is applied for a facile preparation of the Cu-doped cryptomelane by reacting the whole reactants including the dopant in a one pot (known as one-pot synthesis). The CuSO4·5H2O was added to the solution mixtures of KMnO4 and glucose with the molar ratios of 0, 1%, 5% and 10% to KMnO4 (the molar ratio of Cu/Mn is 0; 0.01; 0.05; and 0.10). The as-synthesized pure and Cu-doped cryptomelane-type manganese oxides have been characterized using a wide range of experimental techniques. The XRD was used to identify the phase cystal of manganese oxides, crystallinity and phase purity, whereas AAS was used for the determination of the elemental composition of the samples. The SEM micrographs of the un-doped and doped cryptomelane materials all revealed their same aggregation morphology. The comprehensive N2 sorption analyses confirmed that this synthesized materials are porous materials with the mesopores type and have total BET surface areas in the range of 82-145 m2/g. The effects of the dopant concentration were tested in catalytic degradation of methylene blue using hydrogen peroxide as an oxidant. The results indicated that high Cu-doped concentration resulted in the enhanced degradation of methylene blue. The higher degradation of methylene blue for Cu-doped cryptomelane was correlated with the increase in surface area and total pore volume, but decreased average pore radius.