Facile Synthesis of CoOOH Nanorings over Reduced Graphene Oxide and Their Application in the Reduction of p-Nitrophenol

A facile and one-step route has been employed for the synthesis of highly uniform CoOOH nanorings assembled on the surface of reduced graphene oxide (CoOOH/rGO nanocomposite). The physicochemical properties of the obtained CoOOH/rGO nanocomposite were characterized using X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N-2 physical adsorption (BET) and X-ray photoelectron spectroscopy (XPS). The TEM and SEM results confirmed that CoOOH nanorings (edge length similar to 95 nm) were uniformly decorated on reduced graphene oxide nanosheets using the simple precipitation-oxidation-reduction method. When used as a catalyst for the reduction of p-nitrophenol to p-aminophenol in the presence of excess NaBH4, the resulting CoOOH/rGO nanocomposite exhibited good activity and stability. When the initial concentration of p-nitrophenol was 1.25 x 10(-4) mol center dot L-1, p-nitrophenol could be fully reduced within 3.25 min at room temperature. The apparent rate constant was estimated to be 1.77 min(-1), which is higher than that of pure CoOOH nanorings. Moreover, p-nitrophenol could still be completely reduced within 6 min in the fifth successive cycle. The superior catalytic performance of the nanocomposite is attributed to the synergistic effect between the highly dispersed CoOOH nanorings and the unique surface properties of the reduced graphene oxide nanosheets, which greatly increased the concentration of p-nitrophenol near CoOOH nanorings on reduced graphene oxide surface and improved the local electron density at the interface.