Cobalt-Substituted Heteropolyanion: Synthesis, Characterization, and Application to Oxidation of an Organic Dye in an Aqueous Medium

The present work aimed to remove a toxic organic dye using a recyclable Dawson-type heteropolyanion as a green catalyst. Indeed, a novel molybdenum-substituted heteropolyanion HP₂W₁₅Mo₃Co_2.5O₆₂·20H₂O was synthesized and characterized by EDX, IR, ³¹P-NMR and cyclic voltammetry methods. Thereafter, the synthesized catalyst was used in the oxidation reaction of fuchsine acid (FA) by H₂O₂. As a result, the catalyst exhibited high catalytic activity in the degradation of FA at natural pH and room temperature. The catalytic oxidation efficiency as 97.97% was found after 120 min under catalyst mass of 0.001 g and H₂O₂ concentration of 49 µM. By combining the used process with UV radiation at 365 nm, the FA oxidation time becomes three times lower than that seen in the presence of H₂O₂ only. Moreover, ·OH involvement in dye degradation was confirmed and the H₂O₂ activation mechanism using HP₂W₁₅Mo₃Co_2.5O₆₂·20H₂O as catalyst was proposed. The stability of the recovered catalyst of the FA degradation has been confirmed by IR spectroscopy. Therefore, this study can provide an efficient green way of using cobalt catalyst for environmental remediation.