Fabrication of Ionic Liquid-Modified Onion-like Carbon Nanoparticles Derived from Candle Soot for Synergistically Improved Lubrication Behavior

In this paper, the ionic-liquid-functionalized onion-like carbon nanoparticles (IL@OLC) were successfully prepared via carbonization of candle soot followed by surface modification with an ionic liquid. Initially, a polyethylenimine (PEI) layer cross-linked by epigallocatechin gallate (EGCG) was assembled in situ on the OLC surface. Subsequently, the as-synthesized ionic liquid (IL-Cl) was grafted onto the PEI@OLC surface through the aza-Michael reaction between the C═C bond of IL-Cl and the amine group of PEI. Finally, an ion-exchange reaction replaced Cl^– with PF₆^–, yielding the ionic-liquid-functionalized OLC (IL-PF₆@OLC). The resulting IL-PF₆@OLC exhibits exceptional antiwear properties with a low coefficient of friction (COF). The optimal performance was achieved at an additive concentration of 3.0 wt %, where the average COF of base oil decreased from 0.168 to 0.105, accompanied by an 89.3% reduction in wear volume. In addition, the load-carrying capacity increased from 100 to 400 N. The improved lubricating performance is attributed to the ionic liquid grafting, which enhances the adsorption ability of the OLC in the friction interface, thereby maximizing its rolling effect and surface repair capabilities. Moreover, the N, P, and F elements of the IL-PF₆@OLC participate in tribochemical reactions under friction heat and mechanical force, forming a more stable and continuous protective film.