Design, preparation and characterization of Fe 3 O 4 @SiO 2 @ECH@thiocarbazide@Au( i )@chitosan nanoparticles as a catalyst for the synthesis of 3,4-dihydropyrano[3,2- c ]chromenes

Magnetic iron/silica/linker/gold ions/chitosan nanostructures were synthesized to achieve an efficient and reusable catalyst characterized by X-ray diffraction, scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and inductively coupled plasma optical emission spectrometry. To improve their stability and increase their surface, the obtained multilayer nanocomposites were capsulated in a chitosan and glutaraldehyde network. It was found that the obtained nanoparticles have diameter size of 43 to 72 nm. The optimized nanocatalyst was applied in an efficient and facile procedure for the synthesis of 3,4-dihydropyrano[3,2- c ]chromenes from aromatic aldehyde or aromatic glyoxal, malononitrile, and cyclohaxane-1,3-dione in water at room temperature. The prepared nanocatalyst can be quickly recovered by employing an external magnet and reused several times without significant activity loss.