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Birnessite type manganese oxide (δ-MnO2) was synthesized for use in degradation of the cationic dye methylene blue in aqueous solution. The material was characterized using infrared spectroscopy, X-ray diffraction, and Brunauer-Emmett-Teller (BET) surface area calculations. The removal of the dye from aqueous solutions was evaluated considering the effects of the following variables: pH, manganese oxide concentration, contact time, and temperature. UV-Vis spectroscopy analyses indicated achievement of 99 and 95% removal of methylene blue (7 mg L) at pH 2.0 and 4.0, respectively, after 120 min of contact with the birnessite (100 mg L). At higher pH of 6.0 and 8.0, removals of around 99 and 80%, respectively, were obtained after a longer time of 1860 min. Analyses of total organic carbon (TOC) revealed that 80% reduction of organic matter was obtained at pH 4.0. The method of multivariate curve resolution-alternating least squares (MCR-ALS) was used together with UV-Vis spectroscopy to evaluate the removal process, confirming the degradation of methylene blue. Thionine (λmax = 601 nm) was identified as one of the byproducts of N-demethylation of methylene blue. The results indicated that the degradation process started with N-demethylations of the methylene blue molecule.

Application of a Chemometric Method to Interpret Spectrophotometric Data Obtained for Degradation of an Organic Dye in Water Using Manganese Oxide