Synthesis, characterization and application of sulfonic acid supported on ferrite–silica superparamagnetic nanoparticles

Abstract

In this study, the synthesis of sulfonic acid supported on ferrite–silica superparamagnetic nanoparticles (Fe 3 O 4 @SiO 2 @SO 3 H) as a nanocatalyst with large density of acidic groups is suggested. This nanocatalyst was prepared in three steps: preparation of colloidal iron oxide magnetic nanoparticles (Fe 3 O 4 MNPs), coating of silica on Fe 3 O 4 MNPs (Fe 3 O 4 @SiO 2 ) and incorporation of sulfonic acid as a functional group on the surface of Fe 3 O 4 @SiO 2 nanoparticles (Fe 3 O 4 @SiO 2 @SO 3 H). The properties of the prepared magnetic nanoparticles were characterized using transmission electron microscopy, infrared spectroscopy, vibrating sample magnetometry, X‐ray diffraction and thermogravimetric analysis. Finally, the applicability of the synthesized magnetic nanoparticles was tested as a heterogeneous solid acid nanocatalyst for one‐pot synthesis of diindolyloxindole derivatives in aqueous medium. Oxindole derivatives were produced by the coupling of indole and isatin compounds with good to high yields (60–98%). Copyright © 2016 John Wiley & Sons, Ltd.