Fabrication of GNS/MoS2 composite with different morphology and its tribological performance as a lubricant additive

MoS2 was anchored on the surface of graphene sheets (GNS) with hydrothermal process and chemical vapor deposition to obtain GNS/MoS2 nanoflowers (GNS/MoS2-NFs) and GNS/MoS2 nanoplates (GNS/MoS2 NPs). The GNS/MoS2 composite prepared with different methods was observed with XRD, Raman, SEM, TEM and XPS respectively, and the characterization results confirmed the different morphology of GNS/MoS2-NFs and GNS/MoS2 NPs. For GNS/MoS2-NFs, the MoS2 nanoflowers were dotted on the graphene surface, while the MoS2 nanoplates were uniformly attached on the graphene surface in GNS/MoS2 NPs. The tribological properties of (dibutyl phthalate) DBP containing GNS/MoS2-NFs or GNS/MoS2 NPs was compared with four-ball tribotester at 1200 rpm under 392 N for 30 min. The GNS/MoS2-NFs additive presented better performance than GNS/MoS2 NPs additive even at different concentration. For example, the friction coefficient and wear scar diameter of base oil were reduced by 42.8% and 16.9% with the introduction of 0.02 wt% GNS/MoS2-NFs, while that can only be reduced by 37.6% and 11.9% with the addition of 0.02 wt% GNS/MoS2-NPs. The two additives after friction was further analyzed to explore the lubrication mechanism, and a possible mechanism of GNS/MoS2-NFs was tentatively proposed. In addition, the friction-reducing and anti-wear performance of GNS/MoS2-NFs dispersed DBP can be improved more effectively comparing to that of individual GNS, MoS2 nanoflowers, and the mixture of them. The lubrication mechanism of different additives was investigated with the observation of wear scar, and it indicated that the synergistic effect between GNS and MoS2 nanoflowers played an important role during the friction due to its microstructure.