Confinement of ultrafine Co₃O₄ nanoparticles in nitrogen-doped graphene-supported macroscopic microspheres for ultrafast catalytic oxidation: Role of oxygen vacancy and ultrasmall size effect

Ultrasmall size and abundant defects are two key factors for enhancing the property of catalysts. However, how to simultaneously introduce defects and ultrasmall nanoparticles is still challenging. Herein, oxygen vacancies on confinement of ultrafine Co₃O₄ NPs (6–14 nm) in nitrogen-doped graphene-supported macroscopic microspheres (Co₃O₄@N-rGO) were firstly fabricated and its large-scale applications in peroxymonosulfate activation for eliminating pollutants. Detailed characterizations manifested that ultrafine Co₃O₄ allowed a higher density of active sites to be exposed, the synergy of abundant oxygen vacancies and confinement graphene-supported structure induced the interfacial mass/electron transfer. As expected, Co₃O₄@N-rGO achieved ultra-fast (0.453 min⁻¹) sulfamethoxazole (SMX) degradation and 67.4 % mineralization within 10 min, which greatly outperformed that of Co₃O₄ NPs from ZIF-67 (0.055 min⁻¹). Integrated with ESR and quencher experiments, electrochemical analysis and XPS spectra before and after reaction, the degradation of SMX was dominated by singlet oxygen and other ROS had an auxiliary role. Moreover, a continuous fluidized-column reactor represented a cost-effective method for large-scale industrial wastewater treatment. This work not only verified the coaction of confined and ultrasmall NPs and oxygen vacancy but also provided a generally applicable strategy, thus expanding the applicability of heterogeneous catalysts.