PEG-mediated hydrothermal synthesis of hierarchical microspheres of MoS2 nanosheets and their potential for lubrication application

Lamellar-structured nanomaterials are gaining large interest for tribological applications owing to their remarkable mechanical and low shearing properties. Herein, polyethylene glycol (PEG)-mediated hierarchical microspheres of MoS2 nanosheets are synthesized by a facile and single-step hydrothermal reduction of ammonium molybdate in the presence of thiourea. The PEG functions as a soft templating material and provides hierarchical microspheres of MoS2 nanosheets. Detailed chemical and microstructural features of hierarchical microspheres of MoS2 nanosheets are probed by FTIR, XPS, Raman, XRD, TGA, FESEM, and HRTEM analyses. Each nanosheet of MoS2 microspheres is composed of limited number (10-20) of atomic-thick lamellae as deduced from HRTEM images. The MoS2 microspheres, as additive provide significantly improved lubrication properties for steel tribo-pair by reducing the friction (similar to 21%) and the wear (42%) compared to that of fully formulated 10W40 lubricant. The elemental mapping of worn surfaces revealed the deposition of MoS2 nanosheets on the contact interfaces. The improved lubrication properties are attributed to collective effect of deposition of delaminated MoS2 lamellae on the contact interfaces, low shearing and high mechanical strength of MoS2 nanosheets. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.