Spectroscopic Fingerprints of Graphitic, Pyrrolic, Pyridinic, and Chemisorbed Nitrogen in N-Doped Graphene

Doping and functionalization of graphene significantly
modulate its properties and extend its application potential.
Detailed and accurate chemical characterization of the final
material is critical for understanding its properties and reliable
design of new graphene derivatives. Spectroscopic methods
commonly used for this purpose include Raman, Fourier transform
infrared (IR), and X-ray photoelectron spectroscopy (XPS).
However, the correct interpretation of observed bands is
sometimes hampered by ambiguities when assigning measured
binding energies or IR/Raman peaks to specific atomic structures.
N-doped graphene has many potential applications but can contain
several different chemical forms of nitrogen whose relative
abundance strongly affects the doped material’s properties. We
present clear spectroscopic fingerprints of the various chemical
forms of nitrogen that can occur in N-doped/functionalized graphene to facilitate the identification and quantification of the
different forms of N present in experimentally prepared samples. The calculated XPS binding energies of the N 1s state for
graphitic, pyrrolic, pyridinic, and chemisorbed nitrogen in N-doped graphene are 401.5, 399.7, 397.9, and 396.6 eV, respectively,
and hydrogenation of pyridinic N shifts its peak to 400.5 eV.