Enhanced electron transfer by confinement effect coupled with nitrogen-rich sites of carbon nanorings for peroxydisulfate activation

Carbon materials with unique structures and properties exhibit significant potential as metal-free catalysts for peroxydisulfate (PDS) activation, promoting the efficient degradation of refractory organic pollutants. Herein, a template-confined pyrolysis strategy is proposed to construct hollow nitrogen-rich carbon nanorings (N-CNRs, N 13.15 at.%). The N-CNRs (0.06 g L⁻¹) with porous architecture activate PDS efficiently for the complete degradation of phenol (20 mg L⁻¹) within 18 min at room temperature, achieving a kinetic constant of 0.29 min⁻¹ that is 10 and 29 times higher than those of N-doped carbon nanosheets and carbon spheres, respectively. Comprehensive characterization combined with mechanistic analysis and theoretical calculations reveals that the large specific surface area (985.8 m² g⁻¹) ensures abundant accessible nitrogen active sites, while the unique annular cavity structure facilitates reactant delivery to adjacent confined nanochannels. Serving as confined reaction domains, the nanochannels of N-CNRs enhance PDS adsorption at graphitic N sites and promote the formation of the metastable PDS* intermediate, thereby accelerating the interfacial electron transfer process. This work opens a new avenue for the rational design and fabrication of carbon materials with high nitrogen doping and engineered nanostructure for wastewater treatment.