Synthesis of ultrathin two-dimensional metal-organic framework nanosheets for lubricant additives

Two-dimension (2D) nano materials are diffusely employed as lubricant additives. In this paper, three kinds of ultrathin 2D metal-organic framework (MOF) nanosheets with different metal ions (Ni 2+ , Zn 2+ , and Cu 2+ ) were successfully synthesized by ultrasonic assisted self-assembly under appropriate solvent ratio. Ni-MOF nanosheets as a new additive in 500 N system exhibit the best dispersion stability and lubrication performance, which is related to its maximum absolute value of Zeta potential. Compared with pure 500 N, the best tribological properties were obtained with the addition of 0.1 wt% Ni-MOF nanosheets, reducing friction by 33.2 ± 12.4 % and wear by 98.7 ± 0.14 %. The excellent performance originates from interlayer sliding effect, polishing effect, and tribofilm with concrete structure. The iron oxide particles embedded in the tribofilm play a supporting structrue for the whole tribofilm. The carbonaceous and nitrogenous compounds are filled around the iron oxide particles, which makes tribofilm denser and more smooth. The further friction tests under higher sliding velocity and longer term reveal the potential industrial use of Ni-MOF nanosheets.