The regulation of the microstructure, luminescence and lubricity of multi-element doped carbon nanodots with alkylated diquaternary 1, 4-Diazabicyclo[2.2.2]octane derived dicationic ionic liquids inserted in carbon skeleton

Herein, carbon dots-ionic liquid (CDs-IL) hybrid nanoparticles are synthesized, on the one side, for constructing novel nanostructure with IL inserted into the carbon skeleton, on the other side, for integrating both excellent friction- and wear-reducing abilities. To realize the assumption, the 1,4-Diazabicyclo[2.2.2]octane was used as bridging agent to synthesize bis-functional dicationic ionic liquid with symmetric structure, followed by co-carbonization with carbon precursor to prepare target products under mild conditions. Three anions included bis(salicylato)borate (BScB), hexafluorophosphate (PF6) and bis(trifluoromethanesulphonyl)imide (NTf2) are utilized to tune their physicochemical properties. The chemical and microstructural properties of the products were characterized by NMR, FTIR, Raman mapping spectra, XPS, UV–visible spectra, Fluorescence spectra, SEM, HRTEM and so on. The produced CDs-IL with an average diameter range of 1–3 nm exhibit excitation-dependent maximum fluorescence at 340/405 nm, 440/518 nm and 380/458 nm for CDs-BScB, CDs-PF6 and CDs-NTf2, respectively. The CDs-PF6 is found to exhibit excellent anti-wear and friction-reducing properties as nanoadditives for PEG base fluid, which achieves remarkably improved anti-wear properties (96.5%) and friction-reducing (72.7%) properties simultaneously, owing to the formation of a protective carbon-based layer at the contact regions. Importantly, friction-induced luminescence quenching, transfer and aggregation of the CDs-IL were observed and their correlations were discussed.