Decolorization and mineralization of methylene blue by potassium permanganate

Methylene blue (MB)-permanganate redox reaction has been studied spectrophotometrically in absence and presence of cationic cetyltrimethylammonium bromide (CTAB). The UV–visible spectroscopy reveals the presence of intermediate reaction products (Azure B, Azure A, and thionine) during interaction confirming the real degradation of MB. The gas chromatography-mass spectrometry (GC-EIMS) was used to establish the formation of MB degradation products. The electron transfers lead to a rapid N-demethylation oxidative reaction to form colored intermediary compounds. The key factors ([MnO4−], [MB], [H2SO4], and temperature) that affect the degradation rate of MB solution are analyzed. The redox reaction proceeds through a complex formation between the MB and MnO4−. The position of absorption band of MB was shifted from 666 nm to 603 nm with increasing the reaction time. The degradation efficiency decreases drastically from 82.1 % to 41.8 % in presence of 1.0 mM H2SO4. The results show that the degradation rate in acidic solutions is lower than that in neutral reaction media. The MnO2 was not formed as the product with H2SO4. The degradation efficiency of MB decreases with increasing CTAB concentrations. Sub-micellar inhibitory role of CTAB indicates that the MnO4− interact with positive head group of CTAB, and inhibit the oxidation of MB.