A guanidine-functionalized graphene oxide/Fe3O4 nanocomposite as a magnetically recoverable heterogeneous catalyst for the Hantzsch reaction

In this study, a guanidine-functionalized graphene oxide/Fe₃O₄ nanocomposite (Gu-GO/Fe₃O₄) was synthesized and demonstrated as an efficient and magnetically recoverable catalyst for the synthesis of polyhydroquinoline derivatives via the unsymmetrical Hantzsch reaction under mild conditions. The catalyst was produced by the covalent immobilization of guanidine onto a 3-chloropropyl triethoxysilane-modified graphene/Fe₃O₄ support. The synthesized Gu-GO/Fe₃O₄ nanocatalyst was characterized using FT-IR, SEM, VSM, XRD, and TGA. Optimization studies for the unsymmetrical Hantzsch reaction revealed that 0.005 g of Gu-GO/Fe₃O₄ at 50 °C under solvent-free conditions afforded good to excellent product yields. The catalyst exhibited facile magnetic recovery using an external magnet and retained its catalytic activity and structural integrity after nine reuse cycles. A hot-filtration experiment confirmed the heterogeneous nature of the catalytic system.