Fabrication of chitosan oligosaccharide-functionalized carbon nitride nanosheets as efficient nano-additive for aqueous lubrication

In the pursuit of environmentally friendly tribological systems, water-based lubricants have garnered significant attention, yet issues related to aqueous lubricant still hinder their broader application. In this study, tannic acid (TA) was assembled onto the graphitic carbon nitride (g-C₃N₄) nanosheets via melamine as a cross-linking agent to form TA-g-C₃N₄, followed by the grafting of chito-oligosaccharide (COS, a polysaccharide with amine groups) via a Michael addition reaction, thereby yielding chitosan-oligosaccharide modified g-C₃N₄ nanosheets (COS-g-C₃N₄). The grafting COS imparts COS-g-C₃N₄ with good dispersion stability in water. Compared with pure water, the average friction coefficient of COS-g-C₃N₄ is decreased to 0.20 from 0.57. The improved lubricating behavior arises from the synergistic effect between a friction-induced chemical protective film and the hydration layer. Furthermore, the incorporating COS-g-C₃N₄ into water-based lubricants effectively inhibits bacterial growth during extended storage periods, offering a prospective avenue for the development of multifunctional water-based lubricants.