Covalent organic frameworks embellished with g-C₃N₄ quantum dots as lubricant additives to optimize the lubrication performance

The synergistic effect of multidimensional nanomaterials is an effective strategy to improve the tribological properties of base oils. Herein, an inorganic-organic nanocomposite comprising zero-dimensional g-C₃N₄ quantum dots (g-CNQDs) and two-dimensional NUS-2 modified with cetyltrimethylammonium bromide (CCOF) is developed as an additive for oil-based lubricants. When 3.0 wt% g-CNQDs/CCOF is added as a lubricant additive, the average coefficient of friction and wear volume of PAO-10 base oil decrease from 0.172 to 6.21 × 10⁵ μm³ to 0.095 and 1.12 × 10⁵ μm³, respectively. Moreover, CCOF and g-CNQDs feature abundant oxygen groups that promote adsorption and tribochemical reaction films on worn surfaces. These coherent tribofilms prevent direct surface contact and enhance interfacial interaction. Additionally, g-CNQDs can act as fillers to repair the worn surface, thereby improving lubrication performance. The PAO-10 base oil containing the g-CNQDs/CCOF nanocomposite demonstrates enhanced performance under various loads, frequencies, and temperatures. Additionally, CCOF and g-CNQDs possess plentiful oxygen-containing functional groups that can facilitate the formation of adsorption films and tribochemical reaction films composed of iron oxides and carbonitrides on the worn surface. The continuous and robust tribofilm prevents direct contact between friction pairs and enhances the interaction at the friction interface. Moreover, g-CNQDs can work as fillers to repair worn surface, thereby improving lubrication performance. The PAO-10 base oil containing g-CNQDs/CCOF nanocomposite shows improved performance under various loads, frequencies and temperatures. This work develops a unique g-CNQDs/CCOF nanocomposite as an additive to improve the lubrication performance of lubricant, providing a reference for exploiting novel lubricant additive.