Functional Group Modulation in Carbon Quantum Dots for Accelerating Photocatalytic CO2 Reduction

This study investigates the mechanism behind the enhanced photocatalytic performance of carbon quantum dot (CQD)-induced photocatalysts. Red luminescent CQDs (R-CQDs) were synthesized using a microwave ultrafast synthesis strategy, exhibiting similar optical and structural properties but varying in surface functional group sites. Model photocatalysts were synthesized by combining R-CQDs with graphitic carbon nitride (CN) using a facile coupling technique, and the effects of different functionalized R-CQDs on CO2 reduction were investigated. This coupling technique narrowed the band gap of R1-CQDs/CN, made the conduction band potentials more negative, and made photogenerated electrons and holes less likely to recombine. These improvements greatly enhanced the deoxygenation ability of the photoinduced carriers, increased light absorption of solar energy, and raised the carrier concentration, resulting in excellent stability and remarkable CO production. R1-CQDs/CN demonstrated the highest photocatalytic activity, with CO production up to 77 μmol g-1 within 4 h, which is approximately 5.26 times higher than that of pure CN. Our results suggest that the superior photocatalytic performance of R1-CQDs/CN arises from its strong internal electric field and high Lewis acidity and alkalinity, attributed to the abundant pyrrolic-N and oxygen-containing surface groups, respectively. These findings offer a promising strategy for producing efficient and sustainable CQD-based photocatalysts to address global energy and environmental problems.