Monitoring Electron Transfer Dynamics in WO ₃ /CdS S‐Scheme Heterojunction by Near‐Infrared Femtosecond Transient Absorption Spectroscopy

To solve the problem of severe charge recombination in pure WO₃, the construction of S-scheme heterojunction is an effective approach. This work has successfully prepared WO₃/CdS S-scheme photocatalysts by electrostatic self-assembly. In situ irradiated X-ray photoelectron spectroscopy and in situ irradiated Kelvin probe force microscopy have provided evidence of steady-state spectra of WO₃/CdS S-scheme heterojunction. To monitor the ultrafast S-scheme interfacial electron transfer process, systematic femtosecond transient absorption spectroscopy (fs-TAS) measurements are performed on pure WO₃, CdS and WO₃/CdS. Since pure WO₃ and CdS have similar negative fs-TAS signals in the UV-vis wavelength range, it is difficult to resolve the electron dynamics of these two components in the WO₃/CdS composite. To address this issue, this study effectively distinguishes the fs-TAS signals of WO₃ and CdS by near-infrared fs-TAS for the first time. S-scheme interfacial electron transfer mechanism is confirmed by resolving the quenching dynamics of trap state electrons in the WO₃ and CdS components of WO₃/CdS composite. This work provides new ideas and references for systematic characterization of S-scheme heterojunction photocatalysts.