Harnessing S-scheme COF/CdIn₂S₄ heterojunctions for enhanced photocatalytic performance

Photosynthesis for H₂O₂ production and pollutant degradation is a promising strategy to solve energy shortages and environmental pollution. However, developing photocatalysts with high-efficiency charge separation, migration, and utilization remains a major challenge. Herein, an organic-inorganic S-scheme heterojunction was constructed by integrating a Schiff-base covalent organic framework (COF) with CdIn₂S₄ (CIS). Leveraging the staggered energy band alignment and work function difference between COF and CIS, a built-in electric field (IEF) was established at their interface, which not only enabled rapid interfacial charge transfer but also preserved sufficient redox potentials, thereby achieving enhanced photocatalytic activity. The optimized COF/CIS heterojunction leverages its hierarchical structure, broad visible-light absorption, and efficient S-scheme charge transfer to achieve a high photocatalytic H₂O₂ generation rate of 3247 μmol·g^-1·h^-1 in RhB solution (10 mg·L^-1). An apparent quantum yield (AQY) of 3.87% is attained under 420 nm monochromatic light irradiation, along with a RhB degradation efficiency of approximately 93.2%. Furthermore, the enhanced interfacial charge transfer via the S-scheme heterojunction is elucidated using in-situ irradiated X-ray photoelectron survey spectrum (ISI-XPS) and femtosecond transient absorption (fs-TA) spectroscopy. This work establishes a rational design strategy for IEF regulation in organic-inorganic S-scheme heterojunction photocatalysts, thereby advancing the new prospects for artificial photosynthesis in energy and environmental applications.