Fabrication of ionic liquid-functionalized covalent organic frameworks for friction and wear reduction

Herein, the ionic liquid functionalized covalent organic frameworks (COFs) nanosheets were successfully prepared via solvothermal reaction and then surface modification. Firstly, the COF with –OH groups (COF-OH) can bond with isocyanate (TDI) via the reactions between –OH group of COF-OH and para-NCO group of TDI, then the NH2-ionic liquid ([NH2C2MIm][Br]) can graft onto COF-OH surface (Br-IL@COF-OH) via nucleophilic addition reactions between –NH2 and ortho-NCO group. The as-prepared Br-IL@COF-OH exhibited outstanding lubrication performance as oil-based lubrication additives, with a trace amount addition of 2.0 wt%, the friction coefficient decreases from 0.144 to 0.102, and the wear volume decreases from 1.38 × 104 μm3 to 2.58 × 103 μm3, nearly 81.4%. The remarkable tribological properties are derived from the formation of stable protective film, which is composed of a physical adsorption layer via grafting ionic liquid and the friction film via tribochemical reaction.