A bio-waste-mediated novel fabrication of ZnCr₂O₄ nanoparticles: a heterogeneous catalyst in Biginelli reaction

Nowadays, emerging nanocatalysts have gained much attention in the field of organic transformations for the development of greener chemistry protocols. Also, the Biginelli reaction has gained prominence amidst multicomponent reactions due to the extensive therapeutic significance of the product dihydropyrimidinones (DHPMs). In this work, first-time zinc chromite nanoparticles (ZnCr₂O₄ NPs) were prepared using cow urine (CoU) as a natural source through a biogenic approach. The physicochemical traits of the synthesized ZnCr₂O₄ NPs were investigated via XRD, UV-DRS, IR, FESEM, EDX, HRTEM, and XPS techniques. Furthermore, ZnCr₂O₄ NPs were implemented as a heterogeneous nanocatalyst for sustainable, uncomplicated, and one-pot synthesis of DHPM analogs. The synthetic strategy offers diverse appealing attributes, such as simplicity, bland reaction systems, facile work-up, reusability of catalyst, and excellent yield. Being heterogeneous, the nanocatalyst was simply retrieved after the reaction and reused (up to 5 cycles) in the Biginelli reaction without any noticeable diminishment in catalytic performance. As a result, the current study reveals that creating ZnCr₂O₄ NPs through a simple green approach and evaluating excellent catalytic activity may aid nanochemistry research by opening up new pathways for advanced organic transformations.