New metal-free nanolubricants based on carbon-dots with outstanding antiwear performance

Nanoparticles have already demonstrated a good performance in improving the wear and/or coefficient of friction when used as nanolubricants. Nevertheless, they show two main drawbacks: most of them are metal-based and, therefore, eco-unfriendly, and they are mostly hydrophilic and, consequently, unstable in organic media, which finally drives to aggregation/sedimentation and the loose of the good properties. In this work, we carry out the synthesis of carbon-based nanoparticles for additives in lubricants from two different approaches: either using ionic liquids as carbons source, or using glutathione as carbon source and decorating the so-obtained carbon dots with the big organic cations of the ionic liquid. The final materials (diameters between 2.2 and 3.5 nm) were characterized by TEM, FTIR, XPS, and luminescent methodologies, finding long-term stability of the suspensions in organic media (>= 15 days). Carbon dots obtained directly from the ionic liquids, in particular from methyltrioctylammonium chloride (MTOACDs) have demonstrated to be the best candidate as additive in different base oils (0.1%, w/v) and lubrication regimes, reducing the coefficient of friction about 30% and wear scar in more than 60% in the most extreme of the tested conditions (120 N). Additionally, nanolubricants are metal-free and therefore, more eco-friendly than classic additives. (C) 2020 The Author(s). Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.