Structural-Defect-Mediated Grafting of Alkylamine on Few-Layer MoS<sub>2</sub> and Its Potential for Enhancement of Tribological Properties
Sangita Kumari, Ajay Chouhan, Om P. Sharma, Sruthi Kuriakose, Sherif Abdulkader Tawfik, Michelle J. S. Spencer, Sumeet Walia, Hiroyuki Sugimura, Om P. Khatri
Abstract
Two-dimensional transition-metal dichalcogenides possess inherent structural characteristics that can be harnessed for enhancement of tribological properties by making them dispersible in lube media. Here, we present a hydrothermal approach to preparing MoS2 nanosheets comprising 4–10 molecular lamellae. A structural-defect-mediated route for grafting of octadecylamine (ODA) on 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 yield ODA-functionalized MoS2 (MoS2–ODA). The MoS2–ODA nanosheets exhibit good dispersibility in lube base oil and are used as an additive (optimized dose: 0.1 mg·mL–1) to mineral oil. It is shown that even at low concentration, MoS2–ODA nanosheets significantly reduce the friction (48%) and wear (44%). Microscopy (field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM)) and spectroscopy (Raman and elemental mapping) analyses of worn scars revealed the formation of MoS2-based protective thin films for lowering of friction and wear. This work, therefore, presents a pathway for low-friction lubricants by deploying functionalized low-dimensional material systems.