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

Abstract

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.