Functionalization of carbon nanotubes with magnetic nanoparticles: general nonaqueous synthesis and magnetic properties

A novel approach has been developed to synthesize magnetic nanoparticle and carbon nanotube (CNT) core-shell nanostructures, such as CoO/CNTs and Mn3O4/CNTs, by the nonaqueous solvothermal treatment of metal carbonyl on CNT templates using hexane as the solvent. The morphological and structural characterizations indicate that numerous cubic CoO or tetragonal Mn3O4 nanoparticles are deposited on the surfaces of the CNTs to form CNT-based core-shell nanostructures. It is revealed that the hydrophobic interaction between nanoparticles and CNTs in hexane plays the critical role for the formation of CNT-based core-shell nanostructures. A physical property measurement system (PPMS-9, Quantum Design) analysis indicates that the CoO/CNT core-shell nanostructures show weak ferromagnetic performance at 300 K due to the ferromagnetic Co clusters and the uncompensated surface spin states, while the Mn3O4/CNT core-shell nanostructures display ferromagnetic behavior at low temperature (34.5 K), which transforms into paramagnetic behavior with increasing temperature.