Quaternized carbon dots as efficient catalysts for CO2 cycloaddition under solvent- and cocatalyst-free conditions

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. Br-1-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 degrees C, 8 h, and 0.1 MPa). Furthermore, the catalyst can be easily recycled up to five times.