Sunlight-Driven Fixation of CO₂ to Cyclic Carbonates Using Carbon Dots as a Photothermal Catalyst

Fixation of CO₂ through photocatalytic cycloaddition with epoxides to synthesize cyclic carbonates is an important but challenging process. In this work, carbon dots (CDs) synthesized from gallic acid and polyethylenimine are used for the efficient catalytic cycloaddition of CO₂ with epoxides in the absence of any solvent, additives, and halides, and importantly upon irradiation by natural sunlight. Specifically, carbon dots generated thermal energy and electrons upon solar irradiation, which together with their surface N-sites activated the inert CO₂. Meanwhile, epoxides were activated by the surface hydroxyl and carboxylic groups of the carbon dots, which reacted with activated CO₂ at solar thermal-induced high temperatures. The CDs shows excellent stability and recyclability during the catalysis. A 1000 mmol scale reaction for cyclic carbonate synthesis performed well upon irradiation with natural sunlight in the presence of CDs, showing great potential for the industrial application due to the simple, mild, and energy-saving process.