The novel synthesis of magnetically chitosan/carbon nanotube composites and their catalytic applications.

Chitosan-modified magnetic carbon nanotubes (CS-MCNTs) were synthesized and were investigated by FT-IR, EDX, FE-SEM, elemental analysis, XRD, VSM and TGA. In order to synthesize the CS-MCNTs composites, Fe3O4 decorated carbon nanotubes (CNTs-Fe3O4) were modified with a silica layer by the ammonia-catalysed hydrolysis of tetraethyl orthosilicate (CNTs-Fe3O4@SiO2). Then, CS-MCNTs were successfully grafted on the surface of CNTs-Fe3O4@SiO2via a suspension cross-linking method. The CS-MCNT was found to be an excellent heterogeneous catalyst for the synthesis of 1,4-dihydropyridines (DHPs). The attractive advantages of the present process include short reaction times, milder and cleaner conditions, higher purity and yields, easy isolation of products, easier work-up procedure and lower generation of waste or pollutions. This catalyst was easily separated by an external magnet and the recovered catalyst was reused several times without any significant loss of activity. A combination of the advantages of CNTs, chitosan and magnetic nanoparticles provides an important methodology for carrying out catalytic transformations. Therefore, this method provides a green and much improved protocol over the existing methods.