Enhanced visible light photocatalytic CO2 reduction over direct Z-scheme heterojunction Cu/P co-doped g-C3N4@TiO2 photocatalyst

Recently, graphitic carbon nitride (g-C3N4) has been considered as a promising candidate for high-performance photocatalytic CO2 reduction. However, some drawbacks, such as high charge carriers’ recombination rate and low visible light adsorption, have limited its applications. The co-doping and constructing direct Z-scheme heterostructure have been proved to be effective approaches to enhance the photocatalytic performance of g-C3N4. In this work, phosphorus and copper co-doped g-C3N4 were successfully synthesized and then coupled with different amounts of TiO2(P25) to obtain Cu/P co-doped g-C3N4/TiO2 heterostructures. The results demonstrated that phosphorus and copper doping extended the light adsorption to the visible region, decreased the band gap energy, increased the specific surface area, and suppressed the recombination rate. Moreover, Cu/P co-doped samples exhibited a higher photocatalytic activity compared to single-doped samples. Furthermore, photoluminescence results showed that Cu/P co-doped g-C3N4/TiO2 nanocomposite significantly suppressed the recombination of photogenerated charge carriers resulting in the highest CH3OH generation yield. The optimized CH3OH production yield reached 859 µmol gcat−1, which was about 5 and 11.6 times higher than that of g-C3N4 and TiO2, respectively. In addition, the synthesized catalysts exhibited excellent stability and recyclability after a 30 h reaction for photocatalytic CO2 reduction. Finally, the possible photocatalytic mechanism was proposed.