In the present work, Black Phosphorus Quantum Dots (BPQDs) were synthesized via sonication-assisted liquid-phase exfoliation. The average size of the BPQDs was 3.3 ± 0.85 nm. The BPQDs exhibited excellent dispersion stability in ultrapure water. Macroscale superlubricity was realized with the unmodified BPQDs on rough Si3N4/SiO2 interfaces. A minimum coefficient of friction (COF) of 0.0022 was achieved at the concentration of 0.015 wt%. In addition, the glycerol was introduced to promote the stability of the superlubricity state. The COF of the BPQDs-Glycerol aqueous solution (BGaq) was 83.75% lower than that of the Glycerol aqueous solution (Gaq). Based on the above analysis, the lubrication model was presented. The hydrogen-bonded network and silica gel layer were formed on the friction interface, which played a major role in the realization of macroscale superlubricity. In addition, the adsorption water layer could also prevent the worn surfaces from making contact with each other. Moreover, the synergistic effect between BPQDs and glycerol could significantly decrease the COF and maintain the superlubricity state. The findings theoretically support the realization of macroscale superlubricity with unmodified BPQDs as a water-based lubrication additive.

Frictional losses are one of the main factors affecting the reliability and service life of mechanical components. In this article, black phosphorus quantum dots (BPQDs) were prepared using the sonication exfoliation approach and investigated as aqueous solution lubrication. The prepared BPQDs with average diameters of 3.1 ± 0.6 nm were evenly distributed in pure water and exhibited excellent dispersion stability. Pure water and BPQDs aqueous solution were added at the same amount each time between the ball (GCr15 steel) and the plate (diamond-like carbon coating deposited on the surface of TC4 titanium alloy) to evaluate the differences in their tribological properties. The addition of BPQDs to pure water resulted in a 36.5% reduction in the coefficient of friction (COF) compared to pure water. The calculated wear rates also decreased by 59.0% at the same time (10 N). The initial Hertzian contact pressure ranged from 1000 to 1300 MPa. Additionally, the superior friction reduction and antiwear performance of the BPQD aqueous solution are principally attributable to the tribofilm that forms on the worn surface as well as its adsorption and rolling effect. This work aims to provide some meaningful guidelines for tribologists on the future study of BPQDs with low friction and low wear in the field of solid–liquid composite lubrication systems.