Design/methodology/approach Various mass fractions of g-C3N4 were introduced into the base oil. Combining tribological testing, rheological testing and surface analysis methods, the anti-wear properties and lubrication mechanisms were analyzed. Findings Transmission electron microscopy images revealed that the size of the nanoparticles of g-C3N4 ranges from 10 to 100 nm. Phase analysis of the g-C3N4 sample was conducted using X-ray diffraction. Further, 1.0% mass fraction of g-C3N4 in the base oil provides excellent anti-wear and friction-reducing performance. Compared to the base oil alone, it reduces the average friction coefficient by 63.8% and decreases the wear rate by 43.1%, significantly reducing the depth and width of the wear scar. Energy-dispersive X-ray spectroscopy and scanning electron microscope analysis revealed that the oil sample containing nano g-C3N4 can form a lubricating film on the sliding surface of bearing steel after wear, which enhances the lubricating properties of the base oil. Originality/value The synergistic effect of the base oil and nanoparticles reduces friction and wear and is expected to extend the service life of bearing steel. These findings suggest that incorporating nano g-C3N4 as a lubricant additive offers significant potential for improving the performance of mechanical components. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2024-0456/