Nitrogen-phosphorus codoped biochar prepared from tannic acid for degradation of trace antibiotics in wastewater

This study was designed to develop a one-step pyrolysis process that could efficiently activate peroxymonosulfate (PMS) and degrade tetracycline hydrochloride (TCH) by producing N, and P codoped carbon materials (NPTC₃-800). Furthermore, it exhibited a high specific surface area (658 cm^2 g), a larger pore volume (0.3 cm^3 g), and a certain content of heteroatoms (nitrogen and phosphorus). PMS-activated NPTC₃-800 attained a TCH removal efficiency of over 90% within 40 min, with an observed rate constant (k_obs) of 0.0307 min^-1. Similarly, the materials exhibited strong resistance to ionic interferences and showed broad applicability across various water bodies. Mobility experiments were conducted to further assess the stability of catalyst (92%, 40 h). Non-radical oxidation pathways, particularly including the singlet oxygen (¹O₂), were evidenced to play dominant roles in TCH degradation, as demonstrated by electron paramagnetic resonance (EPR) observations and experiments with free radical quenching. Theoretical calculations demonstrated that the N and P codoped domains substantially improve TCH removal compared to pure biochar. Finally, the proposed degradation pathways for TCH were identified, and the resulting degradation products demonstrated reduced biological toxicity.