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Biochar is an environmentally friendly material with potential applications in water purification. In this study, herb residue nitrogen-doped biochar (N-BC) was fabricated and used to activate peroxymonosulfate (PMS). Characterization and density-functional theory (DFT) studies were conducted to explore the influence of nitrogen doping. Radical scavenging activity and electron paramagnetic resonance (EPR) spectroscopy revealed that non-radical singlet oxygen (1O 2) is the main reactive oxidative species. Additionally, pyridinic-N was shown to play a pivotal role in the 1O 2 -dominated pathway. Three possible degradation pathways were proposed based on the identified degradation intermediates. Batch experiments confirmed that N-BC showed excellent catalytic performance and reusability. The best condition for tetracycline (TC) degradation efficiency (>99%) in 60 min was obtained when the dosage of N-BC was 1 g/L and the concentration of PMS was 5 mM. Furthermore, N-BC showed approximately 65.5% degradation efficiency within 4 cycles. Furthermore, the toxicity of degradation intermediates was examined using ECOSAR and T.E.S.T procedures. This study brings forth a feasible strategy to synthesize biochar. Furthermore, the proposed approach will facilitate the use of biochar in water purification. [Display omitted] • Nitrogen doped biochar was an efficient catalyst for peroxymonosulfate activation. • Non-radical singlet oxygen was the dominant reactive oxidative species. • Nitrogen doped biochar maintained catalytic effect after four cycles. • The toxicity of TC degradation intermediates was evaluated using T.E.S.T and ECOSAR. [ABSTRACT FROM AUTHOR]