Herein we report a one-step approach to the highly efficient synthesis of graphene oxide/Mn3O4 (GO/Mn3O4) hybrids with superior catalytic activities for decomposition of methylene blue (MB) in water. This method exploits the pristine graphene oxide/manganese sulfate (GO/MnSO4) suspension produced by the modified Hummers method as the raw materials, in which GO/MnSO4 has been in situ converted into GO/Mn3O4 hybrid in combination with KOH and air. This atom-economic reaction produces only K2SO4 crystal as the by-product which meets the standard of green chemistry. For catalystic degradation of MB dye at room temperature, the as-prepared GO/Mn3O4 catalysts result in a significant enhancement in the reaction rate compared to that of the bare Mn3O4 particles with the assistance of H2O2. Typically, 50 mL of MB (50 mg L-1) can be 100% decolorized and 77% mineralized with 10 mg of the GO/Mn3O4 hybrid. Such excellent catalytic performance of the GO/Mn3O4 hybrid is mainly attributed to the synergistic effects of GO, Mn3O4, H2O2 and MB molecules. Based on the hydroxyl radical experiments, the catalytic activity of GO/Mn3O4 hybrids for degradation of MB is closely related with the amount of the reactive center dot OH species generated from H2O2. (C) 2014 Elsevier B.V. All rights reserved.