Water-Soluble Graphene Quantum Dots as High-Performance Water-Based Lubricant Additive for Steel/Steel Contact

Abstract

In this work, graphene quantum dots (GQDs) were firstly synthesized via a simple hydrothermal route and then its tribological performances as water-based lubricant additive were evaluated for the first time. The morphological observation by transmission electron microscope indicates that uniform and monodispersed GQDs with a mean diameter of about 2 nm can be obtained. Fourier transfer infrared spectroscopy and X-ray photoelectron spectroscopy characterizations demonstrate that there are abundant hydrophilic groups existed on the as-prepared GQDs including hydroxyl, epoxy, and carbonyl groups, endowing GQDs with good dispersibility in water. Moreover, the tribological performances are investigated by optimal-SRV-IV reciprocation friction tester, and the results indicated that both the friction coefficient and the wear rate of water can be largely reduced through adding the appropriate amount of GQDs. As a result, compared with graphene oxide, GQD was more effective to enhance the tribological performances of water at the relatively low concentration. When the concentration of GQDs aqueous dispersion is 4 mg/mL, the corresponding sample of GQDs-4 shows the excellent tribological performances with a 42.5% reduction of friction coefficient and a 58.5% decrease of wear rate compared with those of the water. These promising performances demonstrate that the prepared GQDs can be employed as a novel water-based lubricant additive to greatly enhance the tribological performances of the water.