Efficient degradation of tetracycline via N-doped carbon derived from discarded PET plastics by boosting peroxymonosulfate activation and singlet oxygen generation

To address the technical challenges posed by antibiotic wastewater treatment and overcoming the limitations of traditional carbon materials in activated persulfate advanced oxidation technology, this study aimed to develop an efficient, stable, and eco-friendly catalytic material for activated peroxymonosulfate (PMS). Ideally, porous carbon-based composite catalysts can be produced using carbon-rich waste polyethylene terephthalate (PET) as raw material. To improve the catalytic performance and overcome this problem, non-metallic dopants are often used as a modification strategy. This paper presents the fabrication of nitrogen (N) enriched porous carbon (NPC) derived from discarded PET plastics utilizing a molten-salt-assisted (ZnCl₂/NaCl) method, with sodium amide (NaNH₂) serving as the N source. The NPC-500 sample showcased an abundant porosity and an elevated surface extent, achieving an impressive 90 % removal efficiency for 20 mg/L of tetracycline (TC). This efficiency was ascribed to the combined action of adsorption and catalytic decomposition. Additionally, the NPC-500 demonstrated a broad pH tolerance range of 3–11, robust environmental durability, and exceptional cycling performance. The results of the reactive oxygen species (ROS) quenching experiments, electron paramagnetic resonance (EPR) signals, electrochemical analyses and in-situ characterizations indicate that the degradation mechanism is primarily governed by non-radical processes, particularly singlet oxygen (${\text{1O}}_2$), which operates through electron transfer mediated by surface-bound reactive complexes. Furthermore, theoretical analysis shows that the addition of N increases the electrostatic potential and changes the electron density distribution of the doping sites, thereby improving the absorption and stimulation of PMS. In summary, this study proposes a new method for efficient recycling of plastic waste and provides a technical and theoretical perspective for the use of N-rich carbon materials to treat organic wastewater.