“…The use of the CVD method requires a catalyst to produce carbon nanotubes-such as commonly used metal catalysts, including nickel (Ni) [12,13], cobalt (Co) [14,15], iron (Fe) [16], or a dual transition metal (Fe-Co) on supporting material like zeolite [17] and silicon (Si) [18]. However, because of its abundance and ease of access, Fe may be the most preferred CVD catalyst.…”