Light control of charge transfer in metal/semiconductor heterostructures for efficient hydrogen evolution: Optical transition versus SPR

Light-induced charge transfer is one of the key factors to affect photocatalytic activity of heterostructures. Significantly, in metal/semiconductor (M/S) heterostructures the direction of charge transfer is relevant to irradiation wavelength in terms of optical transition of semiconductor and surface plasmon resonance (SPR) of metal. To understand the fundamental photophysical process, herein, we developed a facile double-solvothermal route for fabrication of plasmonic/nonplasmonic-metal/TiO2 composites with the aid of glycine. Upon UV-visible-light illumination, occurrence of light absorption in plasmonic-metal/TiO2 composites is originated from optical transition of TiO2 (UV region) and SPR of plasmonic metal (Au, Ag and Cu, visible region), accounting for reverse charge transfer between them confirmed by transient absorption and photocurrent. Albeit small contribution of SPR effect to photo-generated electrons due to ultrafast electron-phonon scattering, the reverse charge transfer can alleviate photocatalytic performance of these heterostructures to enhance. Hence, well understanding the intrinsic photocatalytic mechanism offers a reliable support to selective construction of sophisticated M/S heterostructure-related polynary photocatalytic systems with high activity.