Plasmonic Metal Mediated Charge Transfer in Stacked Core-Shell Semiconductor Heterojunction for Significantly Enhanced CO 2 Photoreduction.

Construction of core-shell semiconductor heterojunctions and plasmonic metal/semiconductor heterostructures represents two promising routes to improved light harvesting and promoted charge separation, but their photocatalytic activities are respectively limited by sluggish consumption of charge carriers confined in the cores, and contradictory migration directions of plasmon-induced hot electrons and semiconductor-generated electrons. Herein, a semiconductor/metal/semiconductor stacked core-shell design is demonstrated to overcome these limitations and significantly boost the photoactivity in CO 2  reduction. In this smart design, sandwiched Au serves as a "stone", which "kills two birds" by inducing localized surface plasmon resonance for hot electron generation and mediating unidirectional transmission of conduction band electrons and hot electrons from TiO 2  core to MoS 2  shell. Meanwhile, upward band bending of TiO 2  drives core-to-shell migration of holes through TiO 2 -MoS 2  interface. The co-existence of TiO 2  → Au → MoS 2  electron flow and TiO 2  → MoS 2  hole flow contributes to spatial charge separation on different locations of MoS 2  outer layer for overall redox reactions. Additionally, reduction potential of photoelectrons participating in the CO 2  reduction is elaborately adjusted by tuning the thickness of MoS 2  shell, and thus the product selectivity is delicately regulated. This work provides fresh hints for rationally controlling the charge transfer pathways toward high-efficiency CO 2  photoreduction.