Revealing Photoinduced Charge Transfer Mechanism of SnO2/BiOBr S-Scheme Heterostructure for CO2 Photoreduction

Abstract

S-scheme heterojunctions can preserve strong redox capacity on the basis of achieving spatial separation of photogenerated carriers. Therefore, a deep comprehension of the photoinduced charge transfer dynamics in S-scheme heterostructures is vital to enhancing photocatalytic properties. Herein, SnO₂/BiOBr S-scheme heterojunctions with tight contact are fabricated with in situ hydrothermal method. The optimal SnO₂/BiOBr exhibits excellent photocatalytic performance for CO₂ reduction, with yields of CO and CH₄ of 345.7 and 6.7 μmol∙g^–1∙h^–1, which are 5.6 and 3.7 times higher than those of the original BiOBr. The photoinduced charge transfer mechanism and dynamics of SnO₂/BiOBr S-scheme heterostructure are characterized by in situ X-ray photoelectron spectrum (XPS) and femtosecond transient absorption spectroscopy (fs-TA). A new fitted lifetime of photogenerated carriers are observed, which could be attributed to interfacial electron transfer of S-scheme heterojunction, further illustrating an ultrafast transfer channel for photoelectrons from SnO₂ conduction band to BiOBr valence band. As a result, the powerful reduced electrons in BiOBr conduction band and the powerful oxidation holes in SnO₂ valence band are retained. This work provides profound comprehension of photoinduced charge transfer mechanism of S-scheme heterojunction.

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