Preparation of immobilized hexamine on Fe3O4/SiO2 core/shell nanoparticles: a novel catalyst for solvent-free synthesis of bis(indolyl)methanes

Hexamethylenetetramine covalently immobilized on silica-coated magnetic nanoparticles is prepared and characterized by XRD, FT-IR, SEM, and VSM. According to SEM pictures, the nanoparticles are mostly spherical in shape, and their size is approximately 46 nm. The catalytic performance of these magnetic nanoparticles for the synthesis of bis(indolyl)methanes was investigated. The catalyst was readily recycled by the use of an external magnetic field and can be reused four times without significant loss of activity. Graphical Abstract