Synthesis and Characterization of CdS@MIL-101(Cr) Nanocomposites via the Ship-in-Bottle Strategy for the Green Catalytic Performance in the Biginelli Reaction

The purpose of making a composite of two materials is to have enhanced activity and properties compared to the individual components. In this work, CdS-decorated MIL-101(Cr) composites are synthesized following the ship-in-bottle approach. Unlike previous reports on making such composites, a Cd-based coordination polymer is used instead of Cd salts as the source of Cd²⁺ for the in situ formation of CdS with a variation in the loading of CdS (5, 10, 20, and 50%) into MIL-101(Cr). Their interactions are well studied with Raman and XPS analyses, which show the peaks for both CdS and MIL-101(Cr), indicating the capture of CdS by MIL-101(Cr). Additionally, microscopic and X-ray diffraction studies are carried out to establish their purity and crystallinity. The band gap values (3.37-2.26 eV) decrease with an increase in the loading of CdS on MIL-101(Cr). The synergistic Lewis acidic properties of 10%CdS@MIL-101(Cr), as compared to bare CdS and MIL-101(Cr), are demonstrated in the synthesis of numerous dihydropyrimidinones that have tremendous medicinal and pharmaceutical values, where it is found to be a highly efficient and recyclable catalyst (requiring no activation) under solvent-free conditions in 2 h at room temperature. A detailed mechanism is proposed for the reaction.