In this study, a novel lubricant additive nitrogen-doped carbon quantum dot (N-CQD) nanoparticle was prepared by the solvothermal method. The synthesized spherical N-CQD nanoparticles in the diameter of about 10 nm had a graphene oxide (GO)-like structure with various oxygen (O)- and nitrogen (N)-containing functional groups. Then N-CQDs were added to MoS2 nanofluid, and the tribological properties for steel/steel friction pairs were evaluated using a pin-on-disk tribometer. Non-equilibrium molecular dynamics (NEMD) simulations for the friction system with MoS2 or MoS2 + N-CQD nanoparticles were also conducted. The results showed that friction processes with MoS2 + N-CQD nanofluids were under the mixed lubrication regime. And MoS2 nanofluid containing 0.4 wt% N-CQDs could achieve 30.4% and 31.0% reduction in the friction coefficient and wear rate, respectively, compared to those without N-CQDs. By analyzing the worn surface topography and chemical compositions, the excellent lubrication performance resulted from the formation of tribochemistry-induced tribofilm. The average thickness of tribofilm was about 13.9 nm, and it was composed of amorphous substances, ultrafine crystalline nanoparticles, and self-lubricating FeSO4/Fe2(SO4)3. NEMD simulation results indicated the interaction between S atoms in MoS2 as well as these O- and N-containing functional groups in N-CQDs with steel surfaces enhanced the stability and strength of tribofilm. Thereby the metal surface was further protected from friction and wear.
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This work was supported by the National Natural Science Foundation of China (No. 51874036) and Beijing Municipal Natural Science Foundation (No. 2182041).
Jiaqi HE. He received his bachelor’s degree in 2017 from China University of Petroleum (East China), China. Now he is a Ph.D. student in University of Science and Technology Beijing, China. His research interests include metal-working lubrication, preparation of nanofluids, and molecular dynamics simulations.
Jianlin SUN. He received his bachelor’s degree in 1985 from the National Defense University of Technology, China and received the Ph.D. degree in 1998 from the Central South University of Technology, China. Now he is a professor of University of Science and Technology Beijing, China. He specializes in friction, wear and lubrication, as well as surface quality control during metal-forming, quantum chemical calculation, and molecular dynamics simulations.
Junho CHOI. He received his bachelor’s degree in 1994 and master’s degree in 1996 from Korea University, Korea. He obtained his Ph.D. degree from The University of Tokyo, Japan, in 2000. Since 2010, he has been an associate professor in the Department of Mechanical Engineering, The University of Tokyo, Japan. His research interests are surface engineering and tribology, including plasma coating, triboelectric nanogenerator, diamond-like carbon films, nano-carbon materials and so on.
Chenglong WANG. He received his master’s degree in 2019 from University of Science and Technology Beijing, China. He is now a Ph.D. student in University of Science and Technology Beijing. His research focuses on metal working, friction and wear, and nano-lubrication.
Daoxin SU. He received his bachelor’s degree in 2019 from Hohai University, China. Now he is a postgraduate student in University of Science and Technology Beijing, China. His research interests are surface quality control and lubrication during metal-forming.
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He, J., Sun, J., Choi, J. et al. Synthesis of N-doped carbon quantum dots as lubricant additive to enhance the tribological behavior of MoS2 nanofluid. Friction 11, 441–459 (2023). https://doi.org/10.1007/s40544-022-0619-4
- carbon-based quantum dots (CQDs)
- molecular dynamics (MD)