Late-model N, B, and P-co-doped carbon dots as additives for friction-reduction and anti-wear

Carbon dots (CDs), a kind of burgeoning carbon-based nanomaterial, were widely used as high-efficiency lubricant additives for promoting the friction-reduction and anti-wear behaviors of green PEG-based lubricating oils. Undoubtedly, advances in CDs-based lubricant additives play a crucial role in enhancing their application prospect and utility value. Recent studies suggest that doping CDs with heteroatoms, especially multiple heteroatoms could remarkably promote their tribological performance. Therefore, the state-of-the-art N, B, and P-co-doped CDs (N,B,P-CDs) with a diameter of approximately 3.8 nm and composed of amorphous structures were synthesized by conveniently "one-step" pyrolyzing the corresponding carbon sources and dopants. Noticeably, the synthetic procedures of N,B,P-CDs were uninvolved in any pre-processing and postprocessing techniques, showing favorable large-scale preparation potential. Adding suitable concentrations of N,B,P-CDs, the friction-reduction, anti-wear, and load-supporting functions of PEG200 base oil can be maximally increased by 38.1 %, 86.2 %, and 66.7 %, respectively, showing outstanding tribological performances. In addition, the tribological behaviors of N,B,P-CDs are evidently better than that of N,B-CDs and P-CDs under identical test conditions, exhibiting a multiatomic synergistic lubrication effect. According to the wear track surface analysis results and previous reports, the excellent tribological performance of N,B,P-CDs attributes to their favorable film-forming ability and nano-lubrication effect in the different friction stages.