Controlling the size and size distribution of magnetite nanoparticles on carbon nanotubes

Nanocomposites composed of carbon nanotubes (CNTs) and magnetite (Fe3O4) nanoparticles were fabricated by using ethylene glycol as reductant at 160 °C. The composites were subsequently annealed under different temperatures in an inert atmosphere. The products were characterized by transmission electron microscopy (TEM), high resolution TEM, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the Fe3O4 transformed from amorphous phase into single crystalline nanoparticles after annealing and that the annealing temperature played a crucial role in controlling the size and the size distribution of Fe3O4 nanoparticles. The average size of Fe3O4 nanoparticles increased with increasing annealing temperature. Meanwhile, the size distribution of nanoparticles became wide with the increase of temperature. It was caused by the gradual decomposition of oleate groups attached on the CNT surface. Magnetic hysteresis loop measurements revealed that crystalline Fe3O4/CNTs displayed superparamagnetic behavior under room temperature.