Ionic liquid (1-aminopropyl-3-methyl-imidazolium bromide) capped carbon dots (CDs_-Br), with a mean particle size of 1.73 nm and poor crystallinity, have been successfully synthesized by a one-pot pyrolysis method. The CDs_-NTf2 were obtained from the CDs_-Br by an anion exchange reaction between Br⁻ and N(CF₃SO₂)₂ ⁻ (NTf2⁻). The NTf2⁻ endowed the CDs_-NTf2 with wonderful dispersion stability in poly(ethylene glycol) (PEG). The tribological performances of CDs_-NTf2 as the lubricant additive for PEG were investigated in detail using a four-ball model by altering the concentration of CDs_-NTf2, the test load and the duration. The results demonstrated that these CD_-NTf2-based additives exhibited excellent friction-reducing and antiwear properties. In particular, the friction coefficient and wear scar diameter (WSD) of lower balls lubricated by PEG under 392 N correspondingly reduced by 70% and 33% when 0.3 wt% of CDs_-NTf2 was introduced. The WSD reduction further increased by 45% when the test load was increased to 600 N. Moreover, the CD_-NTf2-based additives could work for a long time without weakening the lubrication capabilities. The lubricating mechanism of CD_-NTf2-based additives has also been proposed and illustrated that the synergistic lubricating effect of CDs_-NTf2, including film lubrication of IL groups and nano-lubrication of carbon cores such as rolling, mending and polishing effects, might account for their outstanding tribological behaviors. The above results indicate that CDs are expected to be utilized as a kind of designable and high-performance lubricant additive and find wide applications in machinery and equipment.

N-Doped carbon dots (CDs) were directly synthesized with a high yield of 21.85% by one-pot pyrolysis of a gel composed of ethanolamine and 1-carboxyethyl-3-methylimidazolium chloride at 220 °C for 2 h. The as-synthesized CDs with a mean particle size of 7.8 nm were uniform, amorphous, and abundant in nitrogen content (23.15 wt%) and surface groups such as amide and hydroxyl. Thus, the CDs exhibited good water-solubility, bright blue excitation- and pH-dependent fluorescence with a quantum yield of 17.93%, and high ionic strength tolerance. In addition, a CD-based fluorescent sensor towards Cr(VI) ions with favorable sensitivity and selectivity was constructed based on the inner filter effect. Two good linear relationships between the concentration of Cr(VI) ions and the PL quenching efficiency were obtained in the ranges from 0.2 to 2 (R² = 0.9965) and 2–40 μM (R² = 0.9918), and the limits of detection (LOD = 3σ/S) were calculated as 0.018 and 0.25 μM, respectively. Importantly, this sensor was solid and capable of rapidly detecting Cr(VI) ions in tap water with detection ranges of 0.2–2 (R² = 0.9817) and 2–60 μM (R² = 0.9902), LODs of 0.048 and 0.40 μM, and recoveries of 102.1–106%.