CdS/UiO@MIL Nanocomposites with Multiple S-scheme Heterojunctions for Efficient Thioamide Photooxidation.

The strategic design of S-scheme heterojunctions has emerged as an effective approach to optimize charge carrier dynamics in photocatalytic systems. In this work, CdS/UiO-66-NH2@MIL-88B (CdS/UiO@MIL) nanocomposites with multiple S-scheme heterojunctions were successfully fabricated by combining stable metal-organic frameworks with large specific surface area (UiO-66-NH2 and MIL-88B) with CdS nanoparticles and used for the photocatalytic thioamide oxidative cyclization. Photoelectric tests revealed that the nanocomposites had multiple S-scheme heterojunctions, which could significantly improve the electron-hole separation. The average fluorescence lifetime of CdS/UiO@MIL nanocomposites (~15.15 ns) was ~10-fold, ~13-fold and ~6-fold longer than that of UiO (~1.45 ns), MIL (~1.16 ns) and CdS NPs (~2.62 ns), respectively. The CdS/UiO@MIL nanocomposites also exhibited satisfactory yield (~96%) and good photostability for the thioamide oxidative cyclization reaction, with yields ~10-fold higher than those of UiO (~10%), ~19-fold higher than those of MIL (~5%) and ~3-fold higher than those of CdS nanoparticles (~36%), respectively. Systematic investigations reveal that the cascade charge transfer through multiple S-scheme pathways simultaneously preserves strong redox potentials while suppressing recombination losses. This work underscores the potential of hierarchical S-scheme architectures in advancing photocatalytic organic transformations for sustainable chemistry.