Understanding the fundamental function of solid nanoparticle structure on boundary lubrication is of great significance. Here we prepared a series of solid naoparticles including lamellar carbon and molybdenum disulfide (MoS2), spherical MoS2 and carbon, graphene-like C-MoS2 composite, and graphene quantum dots (GQDs), and investigated their tribological properties and mechanism under boundary lubrication in detail. The experimental characterization and analysis found that the spherical nanoparticles can reduce friction and wear by 40% and 80%, depending on the “third body” composed of these nanoparticles and the friction-induced nano-onion debris in the contact area and an easily shearing film formed by the exfoliated nanoslices on the sliding surfaces. Smaller nanosize GQDs allow the friction and wear to be reduced by up to 60% and 91%, which is attributed to the synergistic effect of a densely protective film on the sliding surfaces and the graphene-like debris in the contact area.

To address the poor dispersibility and incompatibility of graphene toward potential applications, we propose an approach to prepare high-density modified graphene sheets by combining solvent exfoliation of graphite with chemical modification of ionic liquids (ILs).

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