Application of a Chemometric Method to Interpret Spectrophotometric Data Obtained for Degradation of an Organic Dye in Water Using Manganese Oxide
AUTOR(ES)
Cosendey, Thaís A.; Neves, Antônio A.; Miranda, Liany D. L.; Queiroz, Maria E. L. R. de; Oliveira, André F. de; Reis, Efraim L.; Gabriel, Wesley L.
FONTE
J. Braz. Chem. Soc.
DATA DE PUBLICAÇÃO
2020-07
RESUMO
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-1) at pH 2.0 and 4.0, respectively, after 120 min of contact with the birnessite (100 mg L-1). 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.
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