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

Developing high-efficieny 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 Delta G 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.