Elucidating the Charge-Separation and Oxidation Dynamics in Fluorenone-COF/CdS S-Scheme Heterojunction for Photocatalytic Benzaldehyde and Hydrogen Production

Abstract

CdS-based photocatalysts offer an efficient route for simultaneous photocatalytic hydrogen evolution and benzyl alcohol oxidation to value-added chemicals. However, the rapid charge recombination, poor oxidation capabilities, and strong photocorrosion of CdS, when used alone, can lead to low productivity of H₂ and benzaldehyde. Herein, we present a novel S-scheme heterojunction through coupling CdS with Fluorenone-COF as the promising oxidation end. The suitable band level and active center of the fluorenone moiety impart strong oxidative capabilities to the fluorenone-based COFs, enabling them to efficiently catalyze the oxidation of benzyl alcohol with a low reaction energy barrier. Furthermore, the intrinsic electric field of the S-scheme heterojunction significantly improves the separation and mobility of photoinduced charge carriers, while effectively suppressing charge recombination, which in turn reduces the corrosive effect of photogenerated holes on CdS. Consequently, the heterojunction significantly improved the yield of both benzaldehyde and hydrogen. In the presence of Pt as a cocatalyst, the production rates of H₂ and benzaldehyde reached 23.38 and 17.36 mmol g⁻¹ h⁻¹, respectively. This work not only addresses the challenges associated with the utilization of electron holes but also provides an effective green and low-carbon pathway to overcome the challenges of low efficiency and high cost in photocatalytic hydrogen production.

Keywords

charge-separation dynamics / covalent organic frameworks / photocatalytic hydrogen evolution / S-scheme heterojunctionbenzyl alcohol oxidation

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