A new model for the synthesis of graphite encapsulated nickel nanoparticles when using organic compounds in an arc-discharge system

Herein we propose a new “three-step” model of synthesizing graphite encapsulated nickel nanoparticles (Ni-GEM), including the pyrolysis reaction of organic compounds which the conventional two-step model ignores. According to the results of XRD, Raman, and TEM, we found that the Ni-GEM synthesized by using both PF resin and benzene vapor as the carbon sources has two favorable characteristics: thicker shells (~5–10 nm) and smaller particle sizes (~30 nm), which are much better than those using only PF resin or PF resin mixed with cyclohexane vapor (thinner shell less than 5 nm and larger particle sizes ~50 nm). Benzene decomposes into large aromatic molecules and tiny graphitic flakes at 1200–3500K, while cyclohexane prefers to decompose and form small hydrocarbon molecules at 1000K. As a result, the two compounds go through two different reaction paths. Benzene will decompose and directly attach onto the surface of Ni nanoparticles, forming smaller sized but thicker shell structured Ni-GEM, while cyclohexane will lead to the formation of amorphous carbon coating on the Ni-GEM. By including the above two distinct hydrocarbon pyrolysis reactions, this study modifies the conventional model and successfully explains the formation processes of Ni-GEM with very different morphologies. Furthermore, the new model may help in controlling the morphologies of other GEM nanoparticles with a number of core-metals. [Display omitted] •The new “three-step” mechanism model of synthesizing GEM nanoparticles in the arc-discharge system is presented.•Using benzene and cyclohexane vapors as the carbon source show different type of outer shell structure.•The synthesis process using PF resin with organic compound vapors are more efficient than the conventional method.