Boosting photocatalytic CO2 methanation through TiO2/CdS S-scheme heterojunction and fs-TAS mechanism study

The conversion of CO₂ into value-added hydrocarbons via photocatalysis holds great promise for sustainable energy, yet achieving high activity and selectivity remains challenging. Herein, a novel TiO₂/CdS heterostructured photocatalyst exhibits exceptional performance in CO₂ photoreduction. The optimized catalyst delivers a 4.2-fold increase in CH₄ production rate compared to pristine TiO₂, with a remarkable 65.4 % selectivity toward CH₄ (34.6 % CO). The enhanced activity arises from the unique morphology, facilitating CO₂ adsorption and mass transfer, and the intimate S-scheme heterojunction between CdS and TiO₂, which boosts charge separation while preserving strong redox potentials. Critically, femtosecond transient absorption spectroscopy (fs-TAS) combined with in situ DRIFTS provides direct evidence for the S-scheme pathway and identifies sulfur sites on CdS as key for stabilizing ∗CH₃O, ∗CHO and ∗CO intermediates, steering selectivity toward CH₄. In addition, theoretical calculations based on density functional theory (DFT) further complement the experimental findings. The calculations confirm the electronic structure characteristics of the S-scheme heterojunction, revealing the energy levels and charge transfer mechanisms at the atomic scale. This not only deepens our understanding of the photocatalytic process but also provides a theoretical basis for further optimizing the photocatalyst design. Overall, our work demonstrates the outstanding performance of the TiO₂/CdS heterostructured photocatalyst in CO₂ photoreduction.