TiO₂ and ZnO Nanoparticles Immobilized on Magnetic Sulfonated Melamine‐Formaldehyde: Structure Identification and Performance as Recyclable Catalysts for the Biginelli Reaction

Abstract

Sulfonated melamine‐formaldehyde (SMF) containing high dispersed TiO2 and ZnO nanoparticles were fabricated into magnetic nanocomposites by two different method material incorporation protocols, including calcination and wet impregnation. Their catalytic performance was investigated toward Biginelli reaction. For the preparation of the first catalyst series, a two‐step protocol was used. Initially, Fe3O4 nanoparticles were coated with SMF (Fe3O4/SMF). Subsequently, they were decorated consecutively with TiO2 (Fe3O4/SMF/TiO2) and ZnO (Fe3O4/SMF/ZnO). The second set of catalysts was prepared using a two‐step process. Fe3O4 nanoparticles were first used to modify SMF (SMF/Fe3O4). Following the initial step, the surface of SMF/Fe3O4 was decorated with both TiO2 (SMF/Fe3O4/TiO2) and ZnO (SMF/Fe3O4/ZnO). To understand the characteristics of the synthesized nanocomposites, a variety of characterization techniques were employed. New catalysts enabled the rapid synthesis (30–45 min) of a range of biologically active 3,4‐dihydropyrimidinones based on the Biginelli reaction with high yields (70–95 % isolated).