Synthesis and characterization of phosphorus–nitrogen doped multiwalled carbon nanotubes

Phosphorus–nitrogen doped multiwalled carbon nanotubes (CN_xP_y) were prepared using a floating catalyst chemical vapor deposition method. Triphenylphosphine (TPP), as phosphorus (P) precursor, was used to control the structure of the CN_xP_y. Transmission electron microscope (TEM) observation indicated that with the increase of TPP amount, the outer diameter and wall thickness of the CN_xP_y gradually increased, while their inner diameter decreased. TEM and backscattered electron imaging revealed that structural changes of the nanotubes could be attributed to the shape change of the catalyst particles, from conical for nitrogen-doped carbon nanotubes (CN_x) to elongated for CN_xP_y, with the addition of TPP. X-ray photoelectron spectroscopy analysis demonstrated that the P content in CN_xP_y can reach as high as 1.9 at.%. Raman analysis indicated that CN_xP_y had a lower crystallinity than CN_x.