Investigation on tribological behaviors of MoS₂ and WS₂ quantum dots as lubricant additives in ionic liquids under severe conditions

Despite excellent tribological behaviors of ionic liquids (ILs) as lubricating oils, their friction-reducing and anti-wear properties must be improved when they are used under severe conditions. There are only a few reports exploring additives for ILs. Here, MoS₂ and WS₂ quantum dots (QDs, with particle size less than 10 nm) are prepared via a facile green technique, and they are dispersed in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm]PF₆), forming homogeneous dispersions exhibiting long-term stabilities. Tribological test results indicate that the addition of MoS₂ and WS₂ QDs in the IL can significantly enhance the friction-reducing and anti-wear abilities of the neat IL under a constant load of 500 N and a temperature of 150 ℃. The exceptional tribological properties of these additives in the IL are ascribed to the formation of protective films, which are produced not only by the physical absorption of MoS₂ and WS₂ QDs at the steel/steel contact surfaces, but also by the tribochemical reaction between MoS₂ or WS₂ and the iron atoms/iron oxide species.