Synergistic catalysis of Co3O4 and graphene oxide on Co3O4/GO catalysts for degradation of Orange II in water by advanced oxidation technology based on sulfate radicals

In this study, the synergistic catalytic mechanism of Co3O4 and graphene oxide (GO) nanocomposite in the heterogeneous activation of peroxymonosulfate (PMS) to generate sulfate radicals was studied. The activation of Co3O4/GO with different Co3O4 loadings in the catalyst [bare graphene oxide (GO), 20% Co3O4/GO, 30% Co3O4/GO, 50% Co3O4/GO, 70% Co3O4/GO, 90% Co3O4/GO, 95% Co3O4/GO, and pure Co3O4] were tested though the degradation of Orange II in water. The results show that the highest performance achieved using the Co3O4/GO catalyst was based on a synergistic catalysis between Co3O4 and GO. Furthermore, a proportional relation exists between Co3O4 and the catalyst. The highest catalytic activity is observed when the Co3O4 loading was about 50% in the catalyst. Co-OH complexes form on the surface of the GO sheet through the direct interaction of Co species with nearby hydroxyl groups or through the dissociation of H2O with Co2+. The formation is proposed to facilitate the heterogeneous activation of PMS. However, a high Co3O4 loading on the GO surface prevents the formation of Co-OH complexes, which is important in the catalytic reaction. (C) 2013 Elsevier B.V. All rights reserved.