Influence of Ni−Co Catalyst Composition on Nitrogen Content in Carbon Nanotubes

TLDR

Quantum‑chemical calculations indicate that nitrogen in carbon nanotubes exists as substitutional and pyridine‑like atoms within the graphite lattice. The authors synthesized nitrogen‑containing CNTs by pyrolyzing acetonitrile at 850 °C over Co/Ni bimaleate‑derived nanoparticles and characterized the resulting structures with electron microscopy, X‑ray diffraction, and X‑ray photoelectron spectroscopy. They found that catalyst composition controls CNT yield, packing quality, and nitrogen content, with a Ni/Co 1:1 ratio producing the highest proportion of pyridine‑like nitrogen.

Abstract

Nitrogen-containing carbon nanotubes were obtained by pyrolysis of acetonitrile (CH3CN) at 850 °C over catalytic nanoparticles formed by the thermal decomposition of Co and Ni bimaleates or their mutual solutions. Structure and composition of synthesized samples were studied by electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that the yield of the nanotubes, the quality of the layer packing, and nitrogen content in the CNx nanotubes depend on the catalyst composition. XPS of the N 1s spectra show that nitrogen atoms are in two different electronic states in the carbon nanotubes. According to quantum chemical calculations these states can be ascribed to nitrogen atoms substituting for carbon atoms in the graphite network and pyridine-like atoms. It was shown that the nanotubes synthesized using catalyst with the ratio Ni/Co 1:1 contain the greatest proportion of pyridine-like nitrogen.