In Situ Green Synthesis of the New Sandwichlike Nanostructure of Mn3O4/Graphene as Lubricant Additives.

Nanoparticles and two-dimensional (2D) nanosheets are well-investigated as lubricant additives, which can significantly reduce frictional energy consumption. However, the tribological properties of the additives will deteriorate because of the occurrence of aggregation in the lubricant and the difficulty in entering the frictional contact area. In the present work, the new sandwichlike nanostructure of Mn3O4 nanoparticles and graphene nanosheets (Mn3O4@G) has been developed by an in situ green synthesis method; i.e., the impurities of Mn2+ ions in crude graphite oxide as the precursor are directly transferred into Mn3O4 precipitate between the graphene sheets. The graphene has a lamellar structure without folds and wrinkles, and the Mn3O4 nanoparticles are not only uniformly anchored on the graphene surfaces but also intercalated in the layers of the graphene nanosheets. The Mn3O4@G exhibits excellent tribological properties and high stability because of a synergistic lubrication effect between the graphene nanosheets and the Mn3O4 nanoparticles. Even at an ultralow concentration (0.075 wt %) and a high temperature of 125 °C, the friction coefficient and the wear depth have been reduced by 75% and 97% compared with base oil, respectively. The synthesis method and the Mn3O4@G nanocomposite have significant potential in various tribological applications for saving energy.