Catalytic degradation of Acid Orange 7 with hydrogen peroxide using CoxOy-N/GAC catalysts in a bicarbonate aqueous solution

Abstract

The cobalt-based heterogeneous catalysts Co_xO_y-N/GAC were prepared by pyrolysis of a cobalt–phenanthroline complex on granular active carbon (GAC) in a nitrogen atmosphere, and tested for the degradation of Acid Orange 7 using hydrogen peroxide as a benign oxidant in a bicarbonate aqueous solution. Characterization by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and electron spin resonance spectroscopy revealed the formation of a cobalt oxide nanoparticle shell with a metallic Co core on the surface of GAC; and the nitrogen substituted the selected carbon atoms during the pyrolysis process and bonded to cobalt. The catalysts were active for dye decolorization in an aqueous solution containing 10 mM H₂O₂ and 5 mM NaHCO₃ at room temperature. They also presented good stability with nearly no loss of cobalt ions after the reaction, in comparison with the high leaching of Co (0.25 mg L⁻¹) from the Co_xO_y/GAC catalyst without nitrogen. The production of intermediates, the formation of reactive radicals and the effect of HCO₃⁻ were also investigated to further explore the efficiency of the catalyst. This study can provide a promising way for the activation of the green oxidant H₂O₂ in a bicarbonate aqueous solution by heterogeneous cobalt catalysts for environmental remediation.