Tuning the nitrogen content and surface properties of nitrogen-doped carbon nanotubes synthesized using a nitrogen-containing ferrocenyl derivative and ethylbenzoate

Abstract

Aligned nitrogen-doped carbon nanotubes (N-CNTs) containing 6.4–15.7 wt% of nitrogen were synthesized by pyrolysis of 3-ferrocenyl-2-(4-cyanophenyl)acrylonitrile as the catalyst in either acetonitrile or a solution of acetonitrile and ethylbenzoate. For comparison, N-CNTs were synthesized by pyrolysis of 3-ferrocenyl-2-(4-cyanophenyl)acrylonitrile in toluene. The effect of oxygen and the carbon source used during synthesis was investigated. The use of 3-ferrocenyl-2-(4-cyanophenyl)acrylonitrile in acetonitrile as a nitrogen and carbon source selectively yielded mainly N-CNTs, while use of toluene as a carbon source yielded both N-CNTs and carbon spheres. Elemental analysis of the N-CNTs synthesized using both acetonitrile and ethylbenzoate (source of oxygen) indicated that addition of oxygen enhanced the nitrogen content of N-CNTs. This was further supported by results from Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy and inverse gas chromatography surface energy analysis. The higher nitrogen-containing N-CNTs were less graphitic and showed a higher base constant (Kb) compared to N-CNTs synthesized without oxygen. Analysis of transmission electron microscopy images showed that the outer diameters of the N-CNTs decreased upon increasing the oxygen composition by mass in the synthesis precursors from 1 to 4 wt% oxygen, the oxygen was derived from ethylbenzoate. In addition, the scanning electron microscopy and XRD revealed that the alignment of N-CNTs increased upon addition of oxygen. Electrical conductivity measurements of N-CNTs showed a negative relationship between the amount of oxygen in the starting materials and the conductivity of N-CNTs.