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.