Graphene oxide and cobalt oxide nanocomposites (Co3O4/GO) are fabricated in situ as heterogeneous catalysts by the decomposition of cobalt nitrate through heat and crystal growth of Co3O4 on the surface of GO sheets in 1-hexanol solvent. The Co3O4/GO catalyst is characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR). X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). Results show that the Co3O4/GO catalysts are large GO sheets decorated homogenously with well-dispersed Co3O4 nanoparticles. Although Co3O4 or GO alone exhibit little catalytic activity, their hybrid (Co3O4/GO) exhibits an unexpectedly high catalytic activity in the degradation of Orange II in water by advanced oxidation technology based on sulfate radicals, and 100% decomposition can be achieved in 6 min. These phenomena suggest a synergistic catalytic activity of Co3O4 and GO in the hybrid. (C) 2012 Elsevier B.V. All rights reserved.