Carbon quantum dots as photogenerated carrier transfer bridges in all-solid Z-scheme ZnIn₂S₄/CQDs/CeO₂ heterostructures for efficient visible-light-driven photocatalytic hydrogen generation

The development of efficient and stable visible-light-driven hydrogen (H₂) generation photocatalysts plays a crucial role in sustainable energy conversion. In this study, we constructed an all-solid Z-scheme heterostructure by integrating carbon quantum dots (CQDs) as a photogenerated carrier transfer bridge between ZnIn₂S₄ and CeO₂. The unique structure of ZnIn₂S₄/CQDs/CeO₂ facilitates the efficient separation and transfer of photogenerated electron-hole pairs, while the CQDs act as a solid-state electron mediator, enhancing interfacial charge transfer and suppressing recombination. Under visible-light irradiation (λ ≥ 420 nm), when the concentration of ZnIn₂S₄ is 40%, the hydrogen generation rate of ZnIn₂S₄/CQDs/CeO₂-2 reaches 7.7 mmol·g⁻¹·h⁻¹, which is 12.8 times higher than that of unmodified ZnIn₂S₄ (0.6 mmol·g⁻¹·h⁻¹) and significantly greater than that of ZnIn₂S₄/CeO₂ (4.2 mmol·g⁻¹·h⁻¹). Furthermore, the all-solid Z-scheme configuration ensures excellent stability, as demonstrated by prolonged cycling tests. We investigated CQDs as a bridge to facilitate the vector transfer of photogenerated electrons from ZnIn₂S₄ to CeO₂ through density functional theory calculations. Additionally, X-ray photoelectron spectroscopy results confirmed the Z-scheme mechanism of photogenerated carrier transfer within the ZnIn₂S₄/CQDs/CeO₂ heterojunction. This study not only demonstrates an effective approach for promoting charge transfer in nanocomposites using CQDs but also provides a new strategy for developing efficient hydrogen evolution photocatalysts without the involvement of precious metals.