Modulating nitrogen species via N-doping and post annealing of graphene derivatives: XPS and XAS examination

Here, we have thoroughly studied the effect of chemistry of graphene derivatives on the composition of N-species after N-doping with the help of core-level spectroscopy techniques. The modulation of the N species by tailoring the functionalization and atomic structure of graphene derivatives prior to chemical N-doping is experimentally demonstrated for the first time. The large extent of non-terminated or phenol-functionalized graphene edges is found to facilitate the formation of pyridinic nitrogen with its relative content exceeding 72%. In turn, the predominant decoration by the pyrazolic moieties is shown for the perforated and carboxyl-derived graphene layers. The thermal annealing at moderate temperatures of ca.345 degrees C is shown to equally readjust the composition of N-species in graphene derivatives regardless of their chemistry, nanostructure, and the initial distribution of the N-species. Further examination of N K-edge X-ray absorption spectra (XAS) pointed out that the oxidation of the graphene layer governs the manifestation of the pi* resonances and configuration of the sigma* resonance. As a result, a set of facile methods to synthesize graphene derivatives with the desired type of the embedded nitrogen species for the optoelectronic and catalytic applications are proposed and crucial features of their identification using core-level spectroscopy techniques are emphasized. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study demonstrates the modulation of N species by tailoring the functionalization and atomic structure of graphene derivatives prior to chemical N-doping. Thermal annealing at moderate temperatures was shown to readjust the composition of N-species in graphene derivatives regardless of their chemistry, nanostructure, and the initial distribution of the N-species. The oxidation of the graphene layer governs the manifestation of pi* resonances and configuration of sigma* resonance.