Mechanistic insight into photocatalytic CO₂ reduction by a Z-scheme g-C₃N₄/TiO₂ heterostructure

Developing high-efficiency and selectivity catalysts for CO₂ reduction reaction (CO₂RR) is significant in converting solar energy to value-added chemicals, and Z-scheme heterostructures are promising materials for photocatalytic CO₂ reduction due to their narrower band gaps and stronger redox reactivity. In this work, via first-principles calculations we have focused on the performance of a Z-scheme triazine-based g-C₃N₄/TiO₂ heterostructure for photocatalytic CO₂ capture and reduction. The results reveal that the band gap of g-C₃N₄/TiO₂ calculated using the HSE06 method is 2.18 eV, which is smaller than those of g-C₃N₄ and TiO₂. The electrons in the conduction band (CB) of g-C₃N₄ have a stronger oxidation ability and holes in the valence band (VB) of TiO₂ have a stronger reduction ability. The electronic properties indicate that the construction of a heterostructure enhances the catalytic performance. According to the CO₂ reduction pathway, the g-C₃N₄/TiO₂ heterostructure has remarkable catalytic activity for CO₂ reduction to CH₄ and CH₃OH; the hydrogenation of CO₂ → COOH^* with a ΔG of 1.29 eV is identified as the rate determining step. The present work not only emphasizes the significance of the Z-scheme heterostructure, but also paves a promising way for photocatalytic CO₂RR. (authors)