Preparation of an activated carbon from hazelnut shells and its composites with magnetic NiFe₂O₄ nanoparticles

A low cost activated carbon was prepared from hazelnut shells by chemical activation with sodium hydroxide at 600℃ in a N₂ atmosphere and then combined with magnetic NiFe₂O₄ nanoparticles by hydrothermal and co-precipitation methods. Samples were characterized by FESEM, TEM, XRD, FT-IR, nitrogen adsorption and magnetic measurements. Results indicated that the NiFe₂O₄ nanoparticles synthesized by the hydrothermal method had a higher saturation magnetization and smaller average particle size than those produced by the co-precipitation method. The specific surface area and total pore volume of the activated carbon decreased from 314 to 288 m²/g and 0.363 9 to 0.333 8 cm³/g, respectively by forming a hybrid with the magnetic NiFe₂O₄ nanoparticles synthesized by the hydrothermal method. NiFe₂O₄ nanoparticles were mainly distributed on the surface, although a few were inside the pores of the activated carbon. Their sizes were the same as those of the original ones. The saturation magnetization of the hybrids was lower than those of the original NiFe₂O₄ nanoparticles due to the existence of the activated carbon. They showed superparamagnetic behavior at room temperature and were easily separated from solutions by an external magnet.