Synthesis of bis(2-ethylhexyl) phosphate modified carbon quantum dots for enhanced oil-based lubrication

Abstract

Carbon quantum dots (CQDs) exhibit excellent lubricating properties in aqueous media, but their application in nonpolar base oils such as polyalphaolefin (PAO) is hindered by poor solubility. Here, we report the synthesis of hydrophobically modified CQDs functionalized with bis(2‑ethylhexyl) phosphate (CQDs‑D2EHPA), which form stable dispersions in PAO4 for over three months. Tribological evaluation shows that a 2 wt% dispersion of CQDs‑D2EHPA reduces the coefficient of friction by 50.7% and wear volume by 41.6% under a 40 N load at room temperature of 25 ℃, and delivers enhanced load‑carrying capacity and long‑term durability. These improvements are ascribed to a synergistic mechanism in which the carbon core acts as a nanoscale bearing and polishing agent, while the organic surface groups undergo friction‑induced reactions to form a protective tribo-film. This work provides a practical strategy for producing oil‑dispersible CQDs and broadens the potential of carbon nanomaterials for advanced lubrication applications.