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The fixation of carbon dioxide (CO2) with epoxide to form cyclic carbonates is industrially important because of the high economic value of the products. Quaternized carbon dots have great potential in CO2 cycloaddition under their high activity and facile synthesis without cocatalysts. Herein, novel quaternized carbon dots were synthesized through a microwave method using citric acid and ethanolamine with different amounts of (2-bromoethyl)trimethylammonium bromide (Br-CDs) or (2-chloroethyl)trimethylammonium chloride (Cl-CDs). All carbon dots were characterized by TEM, XPS, FT-IR, UV-vis and zeta potential analyses as well as elemental analysis. Br1-CD showed the best catalytic activity (99%) and selectivity (99%) for CO2 cycloaddition with styrene oxide to 4-phenyl-1,3-dioxolan-2-one under suitable conditions (120 °C, 8 h, and 0.1 MPa). Furthermore, the catalyst can be easily recycled up to five times. [ABSTRACT FROM AUTHOR]

Carbon dots with good photoelectric properties are usually used as photocatalysts and electrocatalysts, but the good catalytic performance of carbon dots as nanomaterials for thermal catalysis is ignored. Herein, the application of novel efficient catalysts based on carbon dots for the transformation of carbon dioxide (CO2) to carbonates under solvent-free conditions is described. Carbon dots containing carboxyl, hydroxyl, and amine groups were prepared by a microwave technique and employed together with KI, which showed exceptional catalytic activity in the cycloaddition of carbon dioxide with different epoxides. In addition, the catalyst was easily reusable and had stable recyclability. And the catalyst displayed outstanding catalytic performance due to the synergistic effect of carboxyl (–COOH), hydroxyl (–OH), and amine (–NH) groups. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) as new efficient catalysts have been developed for the Knoevenagel condensation reaction and the synthesis of cyclic carbonates under solvent‐free conditions. Six kinds of carbon dots with different numbers of amino groups were synthesized. The amine‐terminated carbon dot (NCDs‐1) was synthesized using arginine and ethylenediamine by a microwave technique, and its catalytic action was studied. NCDs‐1 with the highest numbers of amino groups was used as new metal‐free and effective heterogeneous catalysts to perform essential Knoevenagel condensation and cycloaddition reactions in solvent‐free conditions. 1H NMR was used to demonstrate the Knoevenagel condensation mechanism, in situ Fourier infrared spectroscopy was used to investigate CO2 cycloaddition and a catalytic mechanism was postulated. NCDs‐1 showed a yield of 96.3±1.5 % for Knoevenagel condensation of benzaldehyde and malononitrile. In addition, NCDs‐1/TBAB showed a yield of (97.0±1.0 %) of 4‐phenyl‐1,3‐dioxolan‐2‐one for styrene oxide at 100 °C and 0.1 MPa in 1.5 h. A simple and convenient method for catalytic reactions with amine‐terminated carbon dots was developed. [ABSTRACT FROM AUTHOR]