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 (SO₄^2-) 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.