Structure, composition, and chemical reactivity of carbon nanotubes by selective nitrogen doping

Carbon nanotubes (CNTs) doped with a range of nitrogen contents (0–10 at.%) were prepared via a floating catalyst CVD method using ferrocene, NH3, and xylene or pyridine. XPS and Raman microscopy were used to assess quantitatively the compositional and structural properties of the nitrogen-doped carbon nanotubes (N-CNTs). XPS analysis indicates a shift in and broadening of the C 1s spectra track with increasing disorder induced by selective nitrogen doping. N 1s XPS spectra show three principle types of nitrogen coordination (pyridinic, pyrolic, and quaternary), with the pyridinic-like fraction selectively increased from 0.0 to 4.5 at.%. First-order Raman spectra were fit with five peaks that vary in intensity and width with nitrogen content. The ratio of the D and G bands’ integrated intensities scaled linearly with nitrogen content. Iodimetric titrations were used to gauge the number of reducing sites on as-prepared N-CNTs, representing the first report of nitrogen doping as a means to deterministically effect the chemical reactivities of carbon nanotubes. The reported methodology for the regulated growth and selective nitrogen doping of CNTs presents new ways to study systematically the influence of nanocarbon composition and structure on chemical and electrochemical reactivity for a host of applications.