Environmentally friendly synthesis of Ag/SiO2 nanoparticles using Thymus kotschyanus extract and its application as a green catalyst for synthesis of spirooxindoles

Today, plant extracts based on synthetic procedures have drawn consideration over conventional methods like physical and chemical procedures to synthesize nanomaterials. Green synthesis of nanomaterials has become an area of interest because of numerous advantages such as non-hazardous, economical, and feasible methods with a variety of applications in biomedicine, nanotechnology and nano-optoelectronics and as catalysts for various organic transformations. In this research, silver nanoparticles were deposited on the surface of nano-silica spheres by an in-situ reduction of Ag⁺ ions using an aqueous extract of Thymus kotschyanus aerial parts as a natural reducing and a capping agent. The result recorded from ultraviolet–visible (UV–Vis) spectrometer, Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS) and X-ray powder diffraction supports the biosynthesis and characterization of Ag/SiO₂ nanoparticles. The results indicated that the average size of Ag/SiO₂ nanoparticles is 25–60 nm. The Ag/SiO₂ nanoparticles act as an environmentally friendly heterogeneous catalyst in the synthesis of spirooxindoles via the three-component condensation reaction of isatins, activated methylene reagents, and 1,3-dicarbonyl compounds in aqueous media, and the desired products were obtained with yields ranging from 90 to 98%. The catalyst can be recovered easily and used repetitively without significant loss of catalytic activity.

Graphical abstract