Experimental and Theoretical Studies on Photocatalytic CO2 Reduction to HCOOH by Biomass-Derived Carbon Dots Embedded Phytochemical-Based CdS Quantum Dots

Photocatalytic CO2 reduction provides a sustainable route to combat climate change by converting CO2 into valuable chemicals by using sunlight. This study presents both experimental and theoretical insights into the reduction of CO2 to HCOOH using biomass-derived carbon dots embedded onto phytochemical-based CdS quantum dots. The 0D CDs/CdS QDs(bio) composites exhibit rich sulfur vacancies and a more negative conduction band, effectively inhibiting CdS photocorrosion (SO42-) while enhancing the CO2 adsorption and photocurrent response. Additionally, it reduced PL intensity and increased decay time, suggesting the enhancement of charge separation and suppression of charge recombination. The optimal 0.4CDs/CdS QDs(bio) composite exhibited a remarkable CO2 reduction to HCOOH formation yield of 439.51 μmol g-1 h-1 (apparent quantum yield of 3.81%) while retaining its structural and morphological stability. Density functional theory calculations reveal HCOO* as a key intermediate, confirming the thermodynamic preference for HCOOH formation over CO with a free energy change of -0.71 eV. This study introduces a novel bio-based CdS QDs composite modified with biomass-derived CDs, providing mechanistic insights into photocatalytic CO2 reduction for sustainable fuel production.