Oxidative degradation of methylene blue (MB) by Co2+-HCO3- system with H2O2 in aqueous solution was studied. Nearly complete decolorization of the dye was obtained in less than 50 min in diluted NaHCO3 solution (25 mM) in the presence of only 20 mu M Co2+ 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 Co2+ and HCO3- were observed at different HCO3- concentrations, and the complex [Co(HCO3)](+) formed at intermediate HCO3- concentrations (5-10 mM) was suggested to be more active than the others. (C) 2010 Elsevier B.V. All rights reserved.