Defective heterojunctions in CO₂ photoreduction: Enabling ultrafast interfacial charge transfer and selective methanation

This study achieved the goal of enhancing photocatalytic methane production and selectivity by constructing a S-scheme heterojunction of TiO₂/g-C₃N₄ followed by conducting a mild-temperature hydrogen reduction to remove hydroxyl groups from the catalyst surface, thereby generating rich vacancies-related active sites. The rate of CO₂ photoreduction to CH₄ under pure water from the H₂-Ti-CN sample is around 27.4 μmol g⁻¹ h⁻¹ with 93.6% selectivity, which is 39.1-fold and 5.59-fold that of pristine g-C₃N₄ and TiO₂, respectively. In addition, the DFT calculation indicates that the vacancies created via hydrogen reduction-mediated heterojunctions effectively tune the energy barrier, resulting in a decrease in the production of the two-electron product CO and concurrently improves the selectivity of the eight-electron reaction. The significantly enhanced photocatalytic performance is ascribed to defects fostering ultrafast charge carrier transfer channels and facilitating the transfer of light-excited charges to the surface, thereby enhancing its high redox capabilities in catalytic reactions.