<p>To address the issues of poor accessibility of active sites and mass transfer limitations in the heterogeneous catalytic activation of peroxymonosulfate (PMS), a manganese-based biochar (BMnC) was prepared via citric acid-assisted pyrolysis combined with in-situ redox co-precipitation. Its efficacy in activating PMS for the removal of phenol from water was investigated through systematic characterization, multi-factor degradation experiments, and reactive species quenching assays. The results indicate that BMnC exhibits excellent catalytic activity in PMS activation for phenol degradation. Under the condition of a catalyst dosage of 0.50&#xa0;g L⁻¹, the reaction rate constant reached 0.9476&#xa0;min⁻¹, outperforming pristine biochar and pure MnO₂ The system demonstrated strong environmental adaptability, maintaining high efficiency over a wide pH range of 3–11 and showing good resistance to various coexisting anions. Characterization and mechanistic studies revealed that citric acid modification significantly increased the specific surface area and exposure of active sites on the material. BMnC facilitates the formation of low-valent manganese intermediates (Mn(II)-O–O-SO₃⁻) through interfacial electron transfer, thereby promoting the generation of SO₄^•⁻ and ^•OH radicals, which synergistically work with the ¹O₂ non-radical pathway to achieve efficient phenol degradation. The encapsulation effect of biochar enhanced the chemical stability of the catalyst. This study provides a new strategy for developing efficient and stable manganese-based heterogeneous catalytic materials for the treatment of phenolic organic wastewater.</p>