Modulating Ti t_2g Orbital Occupancy in a Cu/TiO₂ Composite for Selective Photocatalytic CO₂ Reduction to CO

The electronic structure of composites plays a critical role in photocatalytic conversion, whereas it is challenging to modulate the orbital for an efficient catalyst. Herein, we regulated the t_2g orbital occupancy state of Ti to realize efficient CO₂ conversion by adjusting the amount of photo-deposited Cu in the Cu/TiO₂ composite. For the optimal sample, considerable electrons transfer from the Cu d orbital to the Ti t_2g orbital, as proven by X-ray absorption spectroscopy. The Raman spectra results also corroborate the electron enrichment on the Ti t_2g orbital. Further theoretical calculations suggested that the orbital energy of the Ti 3d orbital in TiO₂ is declined, contributing to accepting Cu 3d electrons. As a result, the Cu/TiO₂ composite exhibited an extremely high selectivity of 95.9 % for CO, and the productivity was 15.27 μmol g^-1  h^-1 , which is almost 6 times that of the original TiO₂ . Our work provides a strategy for designing efficient photocatalysis as a function of orbital regulation.