Dialkyl Dithiophosphate-Functionalized Ti₃C₂T_xMXene Nanosheets as Effective Lubricant Additives for Antiwear and Friction Reduction

Surface modification can be used as an effective tool for designing functionalized 2D nanomaterial-based lubricant additives with desirable properties. In this paper, Ti3C2Tx-based nanoadditives are prepared via surface modification with a tannic acid (TA)-Fe3+ complex and then by introducing commercial lubricating additive dialkyl dithiophosphate (DDP) via Michael addition. TA and FeCl3 solutions are used to form a TA-metal complex as the adhesion layer to anchor Ti3C2Tx nanosheets and then modification with a commercial lubricating additive DDP molecule via Michael addition, resulting in the formation of DDP-functionalized MXene nanosheets (DDP-Ti3C2Tx). The experimental results show that the dispersive stability of the as-prepared DDP-Ti3C2Tx in 500SN base oil is greatly improved for more than 1 week. Furthermore, the tribological properties of the DDP-Ti3C2Tx nanosheet additive are evaluated. The results show that the as-prepared DDP-Ti3C2Tx exhibits significant anti-wear and friction reduction abilities with a low coefficient of friction not exceeding 0.11, reduction in the corresponding wear volume by about 87%, and a high load-carrying capacity up to 500 N as a lubricating additive. The tribological properties may be attributable to the good dispersion and the shape of the small sheet, which ensure their entry into the contact area of the friction pair and the formation of a continuous chemical protective film that prevents direct contact and seizure.