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), NH•HO-reduced graphene (NG-NH), and NH-reduced graphene (NG-NH) 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-NH shows a higher catalytic ability than NG-NH, 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 CO. These findings will guide the applications of NG as a catalyst and enrich our understanding of the PDS-phenol reaction system.