Monodisperse Cu nanoparticles @ MoS2 nanosheets as a lubricant additive for improved tribological properties

Monodisperse Cu nanoparticles @ MoS2 nanosheets were prepared via a facile in-situ reduction method. The anchored Cu nanoparticles with average diameters of 8–13 nm were homogeneously decorated on the polydopamine (PDA) functionalized MoS2 nanosheet surface (Cu/PDA/MoS2). The resulting Cu/PDA/MoS2 nanosheets were highly dispersed in sunflower oil because the PDA film provided a large number of active anchoring sites. The tribological performances of the Cu/PDA/MoS2 nanosheets as a sunflower oil lubrication additive were investigated. The Cu/PDA/MoS2 nanosheets demonstrated optimal lubrication properties in all the sliding tests. For 0.5 wt% Cu/PDA/MoS2 nanosheets mixed with sunflower oil, the average friction coefficient and wear scar width were decreased by 37.8% and 28.5% compared with those for the neat sunflower oil, respectively. The excellent lubrication performance can be ascribed not only to the synergistic lubricating effects of the monodisperse Cu nanoparticles and MoS2 nanosheets but also the formation of stable transfer films on the rubbing surfaces. Furthermore, the lubricating mechanism of the Cu/PDA/MoS2 nanosheets was investigated by studying the worn steel disk surfaces via energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS).