Low temperature preparation of hollow carbon nano-polyhedrons with uniform size, high yield and graphitization

Hollow carbon nano-polyhedrons (HCNPHs) were prepared by a simple one-step reaction between NiCl2·6H2O and CaC2 at a low temperature of 250 °C in autoclaves. Characterizations by X-ray diffraction, Raman spectroscopy and electron microscopies demonstrate the formation of bulk quantities of HCNPHs with a uniform size of about 20 nm and a high degree of graphitization. NiCl2·6H2O serves not only as water source to react with CaC2 to create C2H2 gases but also as catalyst precursor to generate Ni nanoparticles which could promote both the pyrolysis of C2H2 into carbon and the graphitization of the pyrolytic carbon around them. The graphitization causes contraction of the carbon shells concomitant with the occurrence of compressive stress on the Ni nanoparticles and with their shapes changing into polyhedrons, thus created stress concentration at apexes is beneficial to squeeze the Ni nano-polyhedrons out of the carbon shells to yield HCNPHs.