Structural Defects-Mediated Grafting of Alkylamine on Few-Layer MoS2 and Its Potential for Enhancement of Tribological Properties.

Two-dimensional transition metal dichalcogenides possess inherent structural characteristics that can be harnessed for enhancement of tribological properties by making them dispersible in the lube media. Here, we present a hydrothermal approach to preparing MoS2 nanosheets comprising 4-10 molecular lamellae. A structural defects-mediated route for grafting of octadecylamine (ODA) on the MoS2 nanosheets is outlined. The unsaturated d orbitals of Mo at the sulfur vacancies on the MoS2 surface are coupled with the electron-rich nitrogen center of ODA and yielded ODA-functionalized MoS2 (MoS2-ODA). The MoS2-ODA nanosheets exhibited good dispersibility in lube base oil and used as an additive (optimized dose: 0.1 mg.mL-1) to mineral oil. It is shown that even with low concentration; MoS2-ODA nanosheets significantly reduce the friction (48%) and the wear (44%). Microscopic (FESEM, AFM) and spectroscopic (Raman and Elemental mapping) analyses of worn scars revealed the formation of MoS2-based protective thin film for lowering of friction and wear. This work, therefore, presents a pathway for low-friction lubricants by deploying functionalized low-dimensional material systems.