A nonradical reaction-dominated phenol degradation with peroxydisulfate catalyzed by nitrogen-doped graphene

Nitrogen doping is a common approach for functionalization of graphene to generate active sites for catalytic reactions. However, the effect of nitrogen content and species within nitrogen-doped graphene (NG) on catalytic phenol oxidation remains largely unaddressed, especially for the peroxidisulfate (PDS) system. In this work, graphene (G), NH₃•H₂O-reduced graphene (NG-NH₃), and N₂H₄-reduced graphene (NG-N₂H₄) with different nitrogen contents were synthesized, and their catalytic abilities in inducing PDS was evaluated. The degradation results indicated that nitrogen doping improved the catalytic ability of G and NG-NH₃ shows a higher catalytic ability than NG-N₂H₄, even though they have similar nitrogen contents. Based on the XPS spectra, among all the doped nitrogen species, the graphitic N made the greatest contribution to the catalytic activity. The scavenger and electron paramagnetic resonance results imply a major contribution of a nonradical mechanism in the NG-PDS-phenol reaction system. Finally, the hydroquinone and p-hydroxybenzoic acid were identified as two intermediate products during the degradation. The decrease in total organic carbon concentration (TOC) after reaction confirmed that phenol was mineralized partially in CO₂. These findings will guide the applications of NG as a catalyst and enrich our understanding of the PDS-phenol reaction system.