High-temperature lubrication has always been a hot topic in the lubricant and grease industry, and is also an essential concern in the high-end equipment sector to be addressed. Carbon quantum dots (CQDs) are an emerging material widely applied in the field of lubrication, owing to their exceptional lubricity and high load-bearing capacity. However, the vulnerability of CQDs to oxidation in air and reduced stability dramatically restrict their high-temperature application capability. In this study, a nanocomposite of amphiphilic polyvinyl pyrrolidone (PVP) homopolymer with excellent lubricating properties and thermal stability, which is hydrogen bonded to CQDs (CQDs@PVP), was designed to achieve low friction and wear of lubricants at high temperatures. The CQDs@PVP are consistently dispersed in both PEG400 and water, and exhibit superior lubricity compared to unmodified CQDs at high temperatures (ranging from 200‒150 ℃ and 90‒50 ℃). Meanwhile, the dense carbon film on the wear surface and the chemically reactive film of iron compounds directly contribute to the enhanced lubrication performance. These analytical results demonstrate the powerful candidacy of CQDs@PVP as a lubrication additive and promote future high-temperature applications of CQDs in industrial production.

In this study, the nanocomposites of MoS₂ nanoparticles (NPs) grown on carbon nanotubes (MoS₂@CNT), graphene (MoS₂@Gr), and fullerene C60 (MoS₂@C60) were synthesized, characterized, and evaluated for potential use as lubricant additives. By using the benefit of the synergistic effect between MoS₂ and carbon nanomaterials (CNMs), these nanocomposites can be well dispersed in polyalkylene glycol (PAG) base oil and show superior stability compared with pure MoS₂ NPs. Moreover, the dispersions of MoS₂@CNT, MoS₂@Gr, and MoS₂@C60 added in PAG have noticeably improved friction reducing and antiwear (AW) behaviors at elevated temperature for comparison with that of PAG and PAG containing CNT, Gr, C60, and MoS₂ NPs, respectively. The enhanced lubricating properties of these nanocomposites were also elucidated by exploring the tribofilm formed on the disc.

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.