Catalyzed oxidative degradation of methylene blue by in situ generated cobalt (II)-bicarbonate complexes with hydrogen peroxide

Oxidative degradation of methylene blue (MB) by Co(2+)-HCO(3)(-) system with H(2)O(2) in aqueous solution was studied. Nearly complete decolorization of the dye was obtained in less than 50 min in diluted NaHCO(3) solution (25 mM) in the presence of only 20 mu M Co(2+) ions. Meanwhile, the conjugated structure and phenyl rings of the MB molecule were destroyed or even broken down into small organic acids and inorganic ions, as indicated by FT-IR spectra and ion-chromatography. Photoluminescence probing and radical scavenging technologies suggested that the reaction of MB degradation in this system mainly involved the generation and participation of hydroxyl radicals. Furthermore, by cyclovoltammetric measurements, the in situ formed different complexes between Co(2+) and HCO(3)(-) were observed at different HCO(3)(-) concentrations, and the complex [Co(HCO(3))](+) formed at intermediate HCO(3)(-) concentrations (5-10 mM) was suggested to be more active than the others. (C) 2010 Elsevier B.V. All rights reserved.