In-situ synthesis of N-doped biochar from swine manure to activate peroxymonosulfate for efficient tetracycline degradation: The key role of electron transfer process

Improper disposal of livestock manure and organic pollution in aquatic environments pose significant global threats. Herein, we propose a sustainable strategy for swine manure (SM) management by converting it in-situ into nitrogen-doped biochar via one-step pyrolysis at 750 °C (NBC750). The NBC750/peroxymonosulfate (PMS) system efficiently degraded organic pollutants, achieving complete tetracycline (TC) degradation with a reaction rate constant (k_obs) of 0.33 min⁻¹, surpassing most previously reported waste-derived heterogeneous catalytic systems. Notably, TC degradation was accelerated under specific environmental scenarios, particularly in the presence of HCO₃⁻ or at pH > 9, highlighting its adaptability to alkaline and bicarbonate-rich environments. Mechanistic studies confirmed two synergistic pathways: (1) Electron transfer dominated by graphitic N (62 % contribution), identified as the primary route; and (2) Radical pathways (38 % contribution), where C=O/O−C=O groups activate PMS to generate ^•OH and SO₄^•−. The NBC750/PMS system demonstrated high potential in practical applications, as suggested by its robust anti-interference capability and stable performance across various water matrices. This work provides an innovative and sustainable approach for in-situ preparation of N-doped biochar catalysts, enabling efficient water pollutant degradation while ensuring safe SM disposal and resource recovery.