Mechanism and efficiency of methylene blue degradation by microwave-induced birnessites with different Mn average oxidation states
The degradation of methylene blue (MB) in simulated wastewater by microwave-induced birnessites (MIB) with different Mn average oxidation states (AOS) via a catalytic oxidation process was investigated. XRD, UV-vis, LC-MS, XPS and spin moment calculation were conducted to investigate the degradation mechanism and process. The results showed that the removal efficiency and removal amount were 99.4% and 49.7 mg/g after 30 min degradation of MB by MIB with sole Mn AOS during a kinetic study. Absorbance peaks of the products had a "blue shift" and the gradual degradation of MB resulted in the formation of C14H13N2OS, C13H11N2OS, C12H8NO2S and C12H9N2 OS according to LC-MS. With the experiment of MB by MIB over different Mn AOS, the lower Mn AOS of birnessites contributed to the higher degradation efficiency. The Mn3+/Mn4+ ratios increased from Bir1 to Bir6, which indicated the Mn AOS of Birnessite enhanced according to the XPS analysis. And computational work on birnessite through CASTEP was further conducted to demonstrate that Mn3+ in [MnO6] octahedron has higher spin magnetic moment than that Mn4+.
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Document Type: Short Communication
Publication date: December 1, 2014
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