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 are successfully fabricated by combining stable metal-organic frameworks with large specific surface area (UiO-66-NH₂ and MIL-88B) with CdS nanoparticles, which are used for photocatalytic thioamide oxidative cyclization. Photoelectric studies reveal that the CdS/UiO@MIL nanocomposites have multiple S-scheme heterojunctions, which can significantly improve the electron-hole separation of the CdS/UiO@MIL nanocomposites. The average fluorescence lifetime of the CdS/UiO@MIL nanocomposites (≈15.15 ns) is ≈tenfold, ≈13-fold, and ≈sixfold longer than those of UiO (≈1.45 ns), MIL-88B (MIL) (≈1.16 ns), and CdS nanoparticles (≈2.62 ns), respectively. The CdS/UiO@MIL nanocomposites also exhibit satisfactory yield (≈96%) and good photostability for the thioamide oxidative cyclization reaction, the yield of which is ≈tenfold, ≈19-fold, and ≈threefold higher than those of UiO (≈10%), MIL (≈5%), and CdS nanoparticles (≈36%), respectively. Our systematic investigations reveal that the constructed multiple S-scheme charge-transfer pathway can effectively suppress charge recombination and maintain strong redox potential. This work provides a new approach to multilevel S-scheme nanomaterials used in sustainable photocatalytic organic transformations.