Green synthesis of Fe2O3 and CuO hybrid nanoparticles and their application in one pot preparation of 3,4-dihydropyrimidin-2(1H)-thiones in water

Maghemite (Fe2O3), copper oxide (CuO), and copper ferrite (CuFe2O4) nanoparticles (NPs) have been synthesized from metal nitrate and walnut shell as an inexpensive agricultural residue by a thermal decomposition method followed by open-air calcination. Also, Fe2O3@CuO NPs and CuO@Fe2O3 NPs (core/shell nanoparticles) have been synthesized by impregnation of metal oxide NPs (core) and metal nitrate solution followed by calcination. These NPs further were characterized using powder X-ray diffraction, Field emission scanning electron microscopy (FE-SEM), SEM elemental mapping, and energy dispersive X-ray spectroscopy (XRD). We find from the FESEM histograms that the average size of all pure and hybrid nanoparticles is less than 70 nm. Optimization of the reaction between benzaldehyde, thiourea and ethyl acetoacetate at mild reaction conditions in the presence of mentioned metal oxide nanomaterials revealed that CuO@Fe2O3NPs in water provides the best results compared to other nanomaterials. In the following, a detailed study was carried out on the Biginelli reaction with other benzaldehydes by CuO@Fe2O3NPs. The remarkable thing is that the catalyst is recyclable and the catalyst was reused up to five times. In reusing the catalyst, the reaction efficiency did not decrease significantly.