Mechanistic Investigations of the Pyridinic N-Co Structures in Co Embedded N-Doped Carbon Nanotubes for Catalytic Ozonation

High-performance and robust catalysts act as core drivers for advanced oxidation technologies for decontamination of water resources. In this study, we used a facile strategy to prepare magnetic and N-doped carbon nanotubes with cobalt encapsulation (Co-N@CNTs) to catalyze ozone for decomposition of aqueous organic pollutants. By regulating the thermal conditions during the synthesis, the derived Co-N@CNTs manifested maneuvered adsorption capabilities. The embedded Co nanoparticles (NPs) not only afforded carbon nanotubes with a magnetic property but also significantly boosted catalytic ozonation due to the synergistic coupling of the Co interface and N-doped graphitic layer. Formation of such a coordinating structure accelerated electron transfer at the interface and increased the conductivity of surface carbon to coordinate a redox reaction. Density functional theory (DFT) calculations and experimental evidence confirmed that cobalt coupled with graphene with pyridinic N dopants was the most favorable structure, which remarkably enhanced ozone adsorption and its dissociation to generate reactive oxygen species (ROS). Intriguingly, the catalytic ozonation underwent different nonradical regimes dependent on the molecular structures of target organics. In terms of ROS, surface-adsorbed atomic oxygen (*O-ad) was responsible for degradation of oxalic acid, while phenolics were primarily degraded by O-3 molecules and singlet oxygen (O-1(2)). This study provides a cost-efficient and recyclable carbocatalyst for wastewater decontamination and new insights into the structure-functional relationships in carbon-based advanced oxidation processes.