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Developing high-performance carbon dot (CD)-based lubricant additives towards non-polar base oils is always challenging because it is an arduous task to gain hydrophobic CDs with high quality. In this work, with the aid of the chemical reaction between hydroxyl groups and lauroyl chloride molecules, the water-soluble CDs-OH derived from the solvothermal method with particularly high particle size regularity were transformed as the oil-soluble CDs-LA by the one-step surface modification process. As expected, the CDs-LA capped by abundant long alkyl chain groups exhibited excellent long-term dispersion stability in non-polar base oil of polyalphaolefin (PAO4) and hence could be served as the additives of PAO4 directly. Under the same test conditions, the tribological performance of CDs-LA was obviously superior to the hydrophobic CDs obtained by the pyrolysis method, implying that the high particle size regularity was beneficial for making full use of the lubrication functions of CDs. Loading 1.7 wt% of CDs-LA made the friction and wear of PAO4 reduced by 32.2 % and 76.4 %, respectively. When the duration prolonged from 20 min to 200 min, the friction reduction of base oil triggered by CDs-LA further enlarged to 46.9 %. The friction-reducing and anti-wear performance of CDs-LA under high loads was also satisfactory. The worn surface analysis results demonstrated that the robust and homogenous boundary lubrication films composed of Fe x O y and CDs have generated on the rubbing surfaces lubricated by CDs-LA/PAO4 dispersion, well accounting for the outstanding friction reduction and wear resistance functions of CDs-LA. [Display omitted] [ABSTRACT FROM AUTHOR]

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 post-processing 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. [Display omitted] • Novel N,B,P-CDs-based lubricant additives for PEG200 base oil were synthesized. • N,B,P-CDs as additives showed great anti-friction and anti-wear functions. • N,B,P-CDs possessed good multiatomic synergistic lubrication effect. • N,B,P-CDs have outstanding film-forming and nano-lubrication effects. [ABSTRACT FROM AUTHOR]

The morphology, thermal stability, phase composition, chemical groups of nanoparticles were characterized, and appropriate thermal process maintains layered structure and weakens the interlayer interaction of the MSH-AHT400. The tribological performances of MSH-AHT400 as lubricant additive are improved due to the decrease of interlaminar shear strength of nanoparticle. Usage of the as-synthesized nanoparticle leads the formation of a-C tribofilm with higher degree of graphitic structural order. Meanwhile, the degree of graphitic structural order of the a-C correlates with the tribological performances positively. The simulations of classical molecular dynamics (CMD) and Ab-initio molecular dynamics (AIMD) confirm the ability of hydroxyl (–OH) and magnesium ions (Mg2+) in transforming base oil into a-C. A tribological mechanism of MSH-AHT400 as lubricant additive is proposed based on the aspects of easier interlaminar cleavage, nano-polishing and filling and repairing of composite tribofilm containing a-C. [Display omitted] • Reduced interlaminar shear strength of MSH-AHT400 enhances tribological properties. • PAO10 is converted into a-C by Mg2+ and –OH from MSH-AHT400 as lubricant additive. • MSH-AHT400 causes higher degree of graphitic structural order of a-C tribofilm. • Composite tribofilm containing a-C accounts for the tribological mechanism. [ABSTRACT FROM AUTHOR]