Interfacial Charge Transfer in ZnO/COF S-Scheme Photocatalyst via Zn─N Bond

Photocatalysis is a promising solution to global energy shortage and environmental problems. Inspired by photosynthesis, multicomponent heterostructured photocatalysts are extensively investigated, and step-scheme (S-scheme) heterojunction has emerged as the theoretical basis for delineating charge transfer processes in predominant heterostructured photocatalysts. However, the specific charge transfer pathway across an S-scheme heterojunction remains elusive from an atomic/molecular perspective. Herein, it is demonstrated that in S-scheme heterojunction photocatalysts composed of imine-based covalent organic frameworks and nanostructured zinc oxide, interfacial Zn─N bonds are formed between the two components and play critical roles as a charge transfer gateway in the S-scheme heterojunction, based on theoretical calculations, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Moreover, mechanisms for enhanced charge transfer across the S-scheme heterojunction are elucidated using femtosecond transient absorption spectroscopy. This work provides new insights into molecular-level understanding of charge transfer mechanisms in S-scheme heterojunction photocatalysts for promoting energy and environmental applications of artificial photosynthesis.