Effective Atomic N Doping on CeO₂ Nanoparticles by Environmentally Benign Urea Thermolysis and Its Significant Effects on the Scavenging of Reactive Oxygen Radicals

Atomic nitrogen doping on CeO₂ nanoparticles (NPs) by an efficient and environmentally benign urea thermolysis approach is first studied, and its effects on the intrinsic scavenging activity of the CeO₂ NPs for reactive oxygen radicals are investigated. The N-doped CeO₂ (N-CeO₂) NPs, characterized by X-ray photoelectron and Raman spectroscopy analyses, showed considerably high levels of N atomic doping (2.3-11.6%), accompanying with an order of magnitude increase of the lattice oxygen vacancies on the CeO₂ crystal surface. The radical scavenging properties of the N-CeO₂ NPs are characterized by applying Fenton's reaction with collective and quantitative kinetic analysis. The results revealed that the significant increase of surface oxygen vacancies is the leading cause for the enhancements of radical scavenging properties by the N doping of CeO₂ NPs. Enriched with abundant surface oxygen vacancies, the N-CeO₂ NPs prepared by urea thermolysis provided about 1.4-2.5 times greater radical scavenging properties than the pristine CeO₂. The collective kinetic analysis revealed that the surface-area-normalized intrinsic radical scavenging activity of the N-CeO₂ NPs is about 6- to 8-fold greater than that of the pristine CeO₂ NPs. The results suggest the high effectiveness of the N doping of CeO₂ by the environmentally benign urea thermolysis approach to enhance the radical scavenging activity of CeO₂ NPs for extensive applications such as that in polymer electrolyte membrane fuel cells.