Photogenerated Carrier Availability Regulates Redox Selectivity in an S-Scheme CdS/CeO2 Heterojunction

Abstract Selectivity is one of the central challenges in organic photocatalysis, yet how the availability of photogenerated carriers at heterointerfaces regulates competing redox pathways is still insufficiently understood. In this work, an S-scheme heterojunction photocatalyst CdS/CeO2 was designed and prepared, and its performance and mechanism were systematically investigated in the photocatalytic reduction of nitrobenzene, oxidative coupling of benzylamine, and selective oxidation of benzyl alcohol. The heterojunction markedly enhances photocatalytic activity, exhibiting 24-, 12-, and 3.4-fold higher activities than pristine CeO2 for the three reactions, respectively. Radical trapping and in situ infrared spectroscopy reveal that the availability of photogenerated electrons is the key factor governing reduction selectivity. In oxidation reactions, suppression of photogenerated holes markedly affects product selectivity, whereas electrons and superoxide radicals mainly contribute to the overall reaction rate through auxiliary oxygen-reduction pathways. Band-structure analysis, work-function calculations, in situ irradiation X-ray photoelectron spectroscopy (ISI-XPS), and electron paramagnetic resonance (EPR) measurements support an S-scheme charge-transfer mechanism, which preserves strongly reductive electrons on CdS and strongly oxidative holes on CeO2. These results establish a direct relationship between interfacial photogenerated-carrier availability and redox-pathway selectivity in CdS/CeO2, providing mechanistic insight into selective photocatalytic redox transformations.