In situ fabrication of carbon dots-based lubricants using a facile ultrasonic approach

Mechanical friction and wear account for approximately one third of the present global energy consumption. However, it is still a challenge to prepare an efficient lubricant using a green and facile methodology. Herein, for the first time, we report an in situ green, high-yield and large-scale preparation of carbon dots (CDs)-based lubricants derived from low-cost precursors, including citric acid (CA), urea and poly(ethylene glycol) (PEG), via facile ultrasonic processing. The as-obtained lubricant without any post-treatment possesses a super-low mean friction coefficient of 0.02 and a wear scar diameter (WSD) of 0.55 mm determined using a four-ball tester under 600 N. To the best of our knowledge, the as-prepared lubricant displays the best friction-reducing and antiwear performance to date. The highly efficient lubricating properties of the as-obtained lubricant should be assigned to the CDs in lubricants with surface passivation, a carbon core and small size, providing a rolling effect.