Mn and P co-doped biochar catalyst for persulfate efficient degradation of tetracycline hydrochloride：Process and mechanism

A novel manganese/phosphorus-doped biochar (Mn/P-C) catalyst was prepared for the degradation of tetracycline hydrochloride (TCH) by activating peroxymonosulfate (PMS). Characterization of the catalyst revealed that Mn/P-C possessed stacked, complex pleated sheets and surface oxygen-containing functional groups, providing abundant active sites. Mn/P-C exhibited superior adsorption and catalytic properties. Nearly complete removal of TCH was achieved under optimal conditions: a PMS concentration of 2 mM, pH 6.51, and catalyst dosage of 0.5 g/L within 120 minutes of reaction time. The reaction rate constant of the system was 0.060 min⁻¹, which was 13.79 times higher than that of pure biochar. XPS characterization before and after the reaction, quenching experiment, and electron paramagnetic resonance (EPR) experiment comprehensively verified the reaction pathway mechanisms. The primary radicals involved were SO₄^•- and O₂^•-, while the ¹O₂ non-radical transfer pathway was also generated on the catalyst surface, enhancing electron transfer and accelerating catalytic degradation. UPLC-MS/MS was used to investigate the main degradation intermediates and the possible transformation pathways were proposed. The toxicity of TCH and its intermediates was evaluated by the quantitative structure-activity relationship (QSAR) method. Theoretical calculations provided deeper insights into TCH degradation pathways through DFT computational analysis. This study confirms that doping biochar with transition metals and nonmetals can synergistically enhance the degradation efficacy of PMS-activated biochar catalysts, providing a novel approach for the application of carbon-based material catalysts in persulfate activation.