Tribological behaviors of Ni-modified citric acid carbon quantum dot particles as a green additive in polyethylene glycol


A novel green lubricating oil additive (carbon quantum dot (CQD) particle-doped nickel (Ni-CQD)) was synthesized from citric acid and nickel acetate. The effects of CQD and Ni-CQD nanoparticles on the tribological behaviors of polyethylene glycol (PEG200) were investigated under different loads and reciprocation speeds. The results indicate that CQD and Ni-CQD particles can both enhance the lubrication properties of PEG200. However, the Ni-CQD nanoparticles enhanced the lubrication properties more than the plain CQD particles did. The average friction coefficient and wear rate of PEG200 containing 2 wt% Ni-CQDs were reduced by 35.5% and 36.4%, respectively, compared to PEG200 containing pure CQDs under a load of 8 N and reciprocation speed of 25 mm/s over 60 min. The friction and wear mechanisms are attributed to the fact that friction induces the Ni-CQDs to participate in the formation of a tribofilm, resulting in a low friction coefficient and wear rate.


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The authors wish to express their gratitude to Mrs. Ziyan Lu and Mr. Lei Wang for their assistance with SEM/EDS and HRTEM testing. Financial support from the National Natural Science Foundation of China (Grant No. 51505121), Anhui University Outstanding Young Talents Foreign Visiting and Training Program (gxgwfx 2018069), Anhui Provincial Natural Science Foundation (Grant Nos.1608085QE119), and Natural Science Foundation Project of the Anhui Education Committee (KJ2017A536) is gratefully acknowledged. Some of the experimental equipment used in this study in the Birmingham Centre for Cryogenic Energy Storage was obtained with support from the Engineering and Physical Sciences Research Council under the Eight Great Technologies: Energy Storage theme (EP/L017725/1).

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Correspondence to Enzhu Hu.

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Zhiqiang TU. He received his bachelor degree in water supply and drainage science and engineering in 2017 from Binjiang College, Nanjing University of Information Technology, Nanjing, China. After then, he was a master student in biological and environmental engineering at Hefei University. His research fields include biomass lubricant additives and biomass carbon quantum dot.

Enzhu HU. He received his master and Ph.D degrees in chemical engineering and environmental protection equipment and monitoring engineering from Hefei University of Technology, in 2011 and 2014, respectively. He joined the Department of Chemical and Materials Engineering at Hefei University from 2015. His current position is an associate professor and the director of the teaching and research Office. He is also a visiting scholar in Darmstadt University of Applied Science, Germany, in 2018. His research areas cover the tribology of biomaterials such as the nano fullerene and carbon quantum dots.

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Tu, Z., Hu, E., Wang, B. et al. Tribological behaviors of Ni-modified citric acid carbon quantum dot particles as a green additive in polyethylene glycol. Friction 8, 182–197 (2020).

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  • friction
  • dynamics
  • joint clearance
  • numerical models
  • impact
  • durability