Carbon Dot-Based Nanofluids as Additives for Mechanical Lubrication

The practical application of carbon dots (CDs) as lubricant additives was tremendously restrained by their complex and time-consuming preparation, separation, purification, and modification procedures. Here, the CD-based nanofluid was in situ prepared by pyrolyzing a deep eutectic solvent for 6 h under 180 °C and directly applied as a versatile lubricant additive of polyethylene glycol (PEG200) and polyalphaolefin (PAO4). At an optimum loading concentration of 3 wt %, the nanofluid distinctly improved the friction-reducing and antiwear properties of base oils. The tribological performance of the nanofluid as an additive was not only much better than that of DES but also far beyond that of the industrial additive of zinc dialkyldithiophosphate. The wear scar surface analyses illustrated that the ester compounds and CDs in nanofluid corporately induced the formation of thick tribofilms on the rubbing surfaces lubricated by PEG200 with nanofluid. These tribofilms composed of iron oxides, CDs, and carbon oxides protected the surface asperities of frictional interfaces from direct contacts, accounting for the distinguished tribological performance of the nanofluid. Considering the prominent tribological performance, S/P free merit, and possibility of preparation on a large scale, the CD-based nanofluid can be a promising lubricant additive in the field of mechanical lubrication.