Lubrication behavior of fluorescent graphene quantum dots hybrid polyethylene glycol lubricant

Graphene quantum dots (GQDs) with a lattice structure and the size of 1.8–3.4 nm were prepared by a simple hydrogen peroxide-containing hydrothermal reaction method using graphene oxide (GO) as a precursor. The hydroxyl group with the cutting effect can cut GO into GQDs with a large number of oxygen-containing functional groups. As polyethylene glycol (PEG) additives, the photoluminescence (PL) properties of well-dispersed GQDs can reflect and monitor the lubrication state between the sliding interfaces because partial GQDs contributed to low friction/wear and occurred the structural transformation. As-modulated hybrid PEG with 0.04 wt% GQDs shows excellent wear reduction ability, and the wear rate is reduced by 40.5%. The formation of a dense disordered carbon film on the sliding surfaces and iron/iron oxide debris with attached GQDs between sliding interfaces contribute to filling the pits and hindering the direct contact of friction pairs, thereby enhancing the wear resistance. This work illustrates that GQDs as a polar lubricant additive have a great application potential in lubrication regulation and monitoring.