Boron-Nitrogen Codoped Carbon Nanosheets as Oil-Based Lubricant Additives for Antioxidation, Antiwear, and Friction Reduction

Leveraging the advantages of shape retention and atomic reconstruction during the carbonizing of crystalline precursors, we demonstrated an efficient strategy to manufacture boron-nitrogen codoped carbon nanosheets (B,N@PCNS) by virtue of pyrolysis combining metal-organic framework (MOF) precursors and B-dopants. Through the regulation of the ratio between reactants, we implemented an ultrahigh-surface heteroatomic doping rate of N at 10.44 atom % and B at 5.60 atom % with homogeneous distribution, which significantly enhanced the compatibility between carbon nanosheets and the lubricant oil PAO10, resulting in outstanding dispersion stability. Expectedly, the hybrid oil with 2.0 wt % B,N@PCNS displayed fascinating tribological performances in multiple aspects: it lowered the mean coefficient of friction to 0.088, promoted the load-carrying ability from 100 to 400 N, and diminished the wear loss by 91.3%. What is most laudable was the dramatic antioxidation property brought about by B doping; the unique radical scavenging effect of B atoms can restrain the decomposition of oil molecules, consequently prolonging the oxidative induction time from 15.7 min of PAO10 to exceeding 90 min with B,N@PCNS and promoting the onset oxidative temperature by 31.4 °C. With the aid of Raman mapping and XPS sputtering analysis, we verified that a complex tribochemical reaction occurred between B,N@PCNS and the steel substrate and induced the formation of a robust protective tribofilm composed of iron oxides, boron oxides, iron borides, and an amorphous carbonaceous compound. Among these, the rigid boron oxides and iron borides pervaded the whole tribofilm and strengthened it as a reinforcing phase, accounting for the tremendous boost in load-carrying and antiwear performances. This work not only puts forward a novel path in the synthesis of multidoped carbon nanosheets with tailored properties but also broadens the cognition of the tribochemical reaction via intuitive characterization.