Synthesis and characterization of nitrogen-doped onion-like carbon nanospheres

Nitrogen doped onion-like carbon nanospheres were synthesized at 300℃ by a one-step autoclave method using calcium carbide and glutamic acid as reactants. The diameter and crystallinity of the spheres were controlled by varying the amounts of reactants. The products from different amount of reactants were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, specific surface area analysis and X-ray photoelectron spectroscopy and an elemental analyzer. The results suggested that nitrogen atoms can be doped into the carbon lattice successfully by this method. Different morphologies of the carbon spheres were obtained by changing the amounts of the reactants. When the reactant ratio of calcium carbide to glutamic acid was 3:1, onion-like carbon spheres with a 30-50 nm diameter were obtained. With an increasing amount of glutamic acid, solid amorphous carbon nanospheres 60-100 nm in diameter were obtained, while with an increasing amount of calcium carbide, identical onion-like carbon spheres were obtained with higher crystallinity. During the reaction, glutamic acid act as an initiator as well as a nitrogen and carbon source, and the five-membered ring compounds from glutamic acid play an important role in forming the carbon spheres, because they provide curvature for the graphite layers, resulting in the formation of an onion-like structure.