High-quality ultra-flat reduced graphene oxide nanosheets with super-robust lubrication performances

The development of high-performance graphene has been driven by increasingly growing industrial demands. Due to the compatibility of high-efficient and low-cost, chemical exfoliation of graphite is currently a common synthesis method of graphene. Unfortunately, there is not an effective chemical way to prepare high-quality graphene nanosheets for industry application. Working under a harsh condition is also a challenge for their engineering application. Herein, high-quality ultra-flat reduced graphene oxide (UF#G) nanosheets with near-perfect integrity were synthesized by a chemical exfoliation method. Taking the advantage of metal ion from the oxidant agent, the manganese compounds are in situ uniformly deposited on the surface of reduced graphene oxide (rGO) nanosheets in a weak alkali environment, thus protecting the nanostructure from being damaged by gaseous products during chemical reduction process. UF#G can reduce the coefficient of friction (COF) and wear depth of the lubricated interfaces by 49% and 93% at a heavy load (2.5 GPa), compared with pure grease (P.G). Especially, the UF#G-based lubricant has superior lubricating stability with long-operating life of more than 216,000 cycles, which is beyond previous results for both state-of-the-art nanocoatings and nanolubricants. UF#G together with the lubricant generate a robust chemical-mixing tribofilm consisting of a carbon-adsorbed layer and a CaSO₄-deposited layer, which is contributed to the super-robust lubrication performances. The ultra-flat nanostructure of UF#G further improves the lubrication by interlayer-sliding effect. This work provides high-quality ultra-flat reduced graphene oxide nanosheets enabled by a novel chemical-exfoliation route with super-robust lubrication performances.