Zwitterionic dopamine sulfonate functionalized carbon quantum dots as water-based lubricant additive for friction and wear reduction

[Display omitted] •Zwitterionic dopamine sulfonate (ZDS) functionalized carbon quantum dots were prepared by hydrothermal reaction and self-assembled method.•The as-obtained CQD-ZDS exhibit good friction reduction and anti-wear abilities as a water-based lubricating additive.•The good lubrication performance is attributed to the stable carbon film and hydration layer. In this work, we have successfully prepared carbon quantum dots with abundant edge-OH (CQDs-OH) via hydrothermal reaction, and then the zwitterionic dopamine sulfonate (ZDS) was self-assembled onto CQDs surface via chemical bond between the catechol group of ZDS and the edge-OH of CQDs. Due to the good dispersion stability of quantum dots endowed by ZDS, CQD-ZDS exhibits excellent lubricating effect as a water-based lubricating additive. Meanwhile, the tribochemical reaction induced by CQD-ZDS can form a stable carbon and metal oxide protective film on the wear surface. Compared with pure water, the average friction coefficient (COF) decreases from 0.5 to 0.11. The hydration process of ZDS modified CQDs is simulated by molecular dynamics simulation, and its lubricating mechanism is explored.