Mussel-inspired organic molybdenum hybrid UiO-66: Ultralow friction lubricating additive of polyethylene glycol

UiO-66 nanoparticles are highly promising candidates for lubricating additives, owing to their favorable mechanical properties and high thermal stability. However, the macroscopic lubrication performance of UiO-66 nanoparticles relying on the ball-bearing mechanism falls significantly short of their microscopic theoretical prediction values. Herein, core–shell structured UiO-66@PDA/MoA nanocomposites were synthesized via a mussel-inspired hybrid strategy using UiO-66 as the core and PDA/MoA layers as the shell. The addition of 0.5 wt% UiO-66@PDA/MoA endowed PEG200 with ultralow friction coefficient (0.0180) and wear volume (6.22 ×10 4 μm 3 ). Compared with PEG200, the introduction of 0.5 wt% UiO-66@PDA/MoA composites decreased the friction coefficient by 50.7% and wear volume by 49.1%. The ultralow friction behavior of UiO-66@PDA/MoA nanocomposites was attributed to the synergistic lubrication of the PDA/MoA layer and UiO-66. Raman spectroscopy and first-principles calculations demonstrated that the introduction of MoA molecules promoted the formation of carbonaceous components with higher graphitization degree in the tribofilm. This design concept of integrating nano-MOF with organic molybdenum provides a novel strategy for developing lubricant additives with ultralow friction.