Covalently attached strategy to modulate surface of carbon quantum dots: Towards effectively multifunctional lubricant additives in polar and apolar base fluids

Abstract Carbon quantum dots with multifunctional properties (CQDs -N ) as lubricant additive in polar base fluid of bio-based castor oil (CO) were first studied. Followed, a liquid-like CQDs -N with oleylamine capped on the surface ( O -CQDs -N ) was achieved through chemical grafting route, which could dissolve in apolar base fluid of polyalphaolefin (PAO). Either CQDs -N or O -CQDs -N exhibited excellent dispersion stabilities in CO and PAO, which not only endowed them with enhanced anti-wear performance, but also anti-oxidant performance. The carbon quantum dots-based nanoparticles deposited on the worn surface unevenly and formed a thin protective film containing iron oxides, inorganic carbon and nitrogen. Furthermore, the deposited carbon was proved to produce more defects and disordered structure when test load increased, which enhanced the lubricating performance and loading capacity of base fluids.