<p>Nano graphitic carbon nitride (g-C₃N₄) exhibits properties that are strongly influenced by its synthesis method. Vacuum freeze-drying can effectively increase the specific surface area of nanomaterials and enhance their dispersion and stability in lubricating oil. In this study, nano g-C₃N₄ was prepared using vacuum freeze-drying and compared with samples obtained via conventional oven drying. The tribological behavior of different lubricant samples was evaluated using a reciprocating friction tester, and the wear scars were characterized by SEM and EDS. Tribological performance tests of different lubricants were conducted, and SEM and EDS characterizations of wear scars were performed. The results demonstrate that g-C₃N₄ prepared by vacuum freeze-drying exhibits a higher specific surface area, a more defined layered structure, and superior dispersion stability. Compared with the base oil, the F3 sample (containing 1.0 wt.% of freeze-dried g-C₃N₄) exhibited an approximately 50% reduction in average friction coefficient and a 65.57% decrease in wear rate, with a noticeably smoother wear surface. SEM and EDS results revealed that the freeze-drying promoted the formation of a more uniform in-situ tribofilm on the surface of the tribo-pairs. The results indicate that freeze-dried nano g-C₃N₄ shows great potential in facilitating in-situ tribofilm formation and friction reduction.</p>