Verifying the Charge-Transfer Mechanism in S-Scheme Heterojunctions Using Femtosecond Transient Absorption Spectroscopy.

Abstract

S-scheme heterojunction is flourishing in photocatalysis because of the concurrent realization of separated charge carriers and sufficient redox ability. The steady-state charge transfer has been confirmed by other methods. However, an essential part, the transfer dynamics in S-scheme heterojunction, is still missing. To compensate, a series of cadmium sulphide/pyrene-alt-difluorinated benzothiadiazole heterojunctions are constructed and the photophysical processes are investigated through femtosecond transient absorption spectroscopy. Encouragingly, an interfacial charge transfer signal is detected in the spectra of heterojunction, which provides solid evidence for S-scheme charge transfer to complement the results from well-established methods. Further, the lifetime for interfacial charge transfer is calculated to be ~78.6 ps. Moreover, the S-scheme heterojunction photocatalysts exhibit higher photocatalytic 1,2-diols conversion and H2 production rates than bare cadmium sulphide.