All-in-one ultrathin nanoporous ZnIn2S4 with ameliorated photoredox capability: harvesting electron–hole pairs in cooperative hydrogen and benzaldehyde production

Abstract

The coupling of photoredox reactions utilizing both photogenerated electrons and holes has garnered significant attention for producing high-energy-density fuels and value-added products at the same time. In this work, all-in-one porous ultrathin ZnIn₂S₄ nanosheets were developed via a facile one-pot solvothermal method by carefully tuning the concentration of trisodium citrate in the synthesis medium. With the appropriate amount of trisodium citrate, the morphology structure of ZnIn₂S₄ can be modulated into 4–6 nm ultrathin layered sheets with noticeable nanopores of 10–70 nm, which exposes more active sites for the redox activity. The resultant cocatalyst-free ZnIn₂S₄ system was successfully employed in the photocatalytic H₂ evolution coupled with benzyl alcohol oxidation to produce H₂ fuel and benzaldehyde in the absence of sacrificial agents. The porous ZnIn₂S₄ nanosheets with ameliorated light absorption and enhanced redox capability achieved an optimal hydrogen yield of 22.2 mmol g⁻¹ under 4 h simulated sunlight irradiation (AM 1.5), double that of its pristine form, resulting in an apparent quantum efficiency (AQE) value of 5.41% at 380 nm and a solar-to-hydrogen (STH) value of 0.204%. Interestingly, a highly selective (96%) benzaldehyde production of 0.33 mmol h⁻¹ was observed concurrently with simultaneous benzyl alcohol conversion. In situ electron paramagnetic resonance (EPR) reveals that the high-selectivity benzaldehyde formation is attributed to the carbon-centered (Cα) radical-induced pathway with the direct involvement of the photogenerated holes in the C–H bond activation. Overall, this study highlights the importance of the morphology–activity relationship, providing valuable insights for the development of superior all-in-one ultrathin photocatalysts toward ameliorated dual-redox photocatalytic reactions.