Regulating photocatalytic CO2 reduction selectivity via steering cascade multi-step charge transfer pathways in 1 T/2H-WS2/TiO2 heterojuncitons

Due to the high stability of CO2 and slow multi-electron transfer kinetics, photocatalytic reduction of CO2 into multi-electron product CH4 with high selectivity is still a big challenge. Herein, multiphasic WS2 nanosheets composed of metallic 1 T phase and semiconducting 2H phase were integrated with TiO2 nanoparticles to construct a novel ternary heterojunction photocatalyst (1 T/2H-WS2/TiO2) for selective photocatalytic CO2 reduction into CH4. In this heterojunction photocatalyst, an efficient cascade charge transfer channel from TiO2 to 2H-WS2 and subsequently transferred to 1 T-WS2 is formed, which accelerates the charge separation and enables enough electrons enriched on the surface of 1 T-WS2 acting simultaneously as the co-catalyst, resulting in the high selectivity of CH4. The optimized 1 T/2H-WS2/TiO2 photocatalyst showed a higher CH4 yield of 36.44 μmol·g−1·h−1 with a selectivity reaching 94.2%, which was much higher than those of TiO2 (41.9%), 1 T-WS2/TiO2 (80.6%) and 2H-WS2/TiO2 (13.4%). This novel design provides a valuable research reference for regulating the photocatalytic CO2 reduction selectivity via steering the cascade multi-step charge transfer pathways through phase engineering.