Effects of bimetallic catalysts on synthesis of nitrogen-doped carbon nanotubes as nanoscale energetic materials

Well aligned nitrogen-doped carbon nanotubes (CNx-NTs), as energetic materials, are synthesized on a silicon substrate by aerosol-assisted chemical vapor deposition. Tungsten (W) and molybdenum (Mo) metals are respectively introduced to combine with iron (Fe) to act as a bimetallic co-catalyst layer. Correlations between the composition and shape of the co-catalyst and morphology, size, growth rate and nitrogen doping amount of the synthesized CN x -NTs are investigated by secondary and backscattered electron imaging in a field emission scanning electron microscope (FESEM) and X-ray photoelectron spectrometer (XPS). Compared to pure iron catalyst, W-Fe co-catalyst can result in lower growth rate, larger diameter and wider size distribution of the CN x -NTs; while incorporation of molybdenum into the iron catalyst layer can reduce the diameter and size distribution of the nanotubes. Compared to the sole iron catalyst, Fe-W catalyst impedes nitrogen doping while Fe-Mo catalyst promotes the incorporation of nitrogen into the nanotubes. The present work indicates that CN x -NTs with modulated size, growth rate and nitrogen doping concentration are expected to be synthesized by tuning the size and composition of co-catalysts, which may find great potential in producing CNx-NTs with controlled structure and properties.