Alkali modification and nitrogen doping synergistically regulate sludge-derived biochar for persulfate activation and organic pollutant degradation

• Synergistic modification of sludge biochar via alkaline treatment and nitrogen doping. • The 0.5-SSB-3/PMS system achieved over 90% degradation efficiency for RhB within 20 min. • 1 O 2 and pyridinic-N were identified as the primary active species. • The catalyst maintained a degradation efficiency of 90.7% for RhB after five repeated uses. Given the increasing organic pollution in industrial wastewater and the disposal risks of municipal sludge, developing advanced oxidation technology based on sludge-derived biochar-activated peroxymonosulfate (PMS) is highly promising. In this study, a series of sludge-derived biochars (SSB) were prepared via alkali modification and nitrogen doping, and their performance and mechanism in activating PMS for the degradation of organic pollutants were systematically investigated. After alkali modification, the surface of biochar becomes much rougher, and meanwhile the functional group C=O appears. After urea doping, the biochar exhibits a more porous characteristic, and the increased nitrogen species can enhance the electron transfer ability. Experimental results demonstrated that the 0.5-SSB-3/PMS reaction system could rapidly oxidize and degrade multiple organic pollutants. Characterization via SEM and BET revealed that the modified biochar has a rough surface and a relatively distinct pore structure, while both its pore size and pore volume are increased. Mechanistic investigations revealed that non-radical singlet oxygen ( 1 O 2 ) served as the dominant reactive species. On the one hand, it is generated by the self-decomposition of PMS; on the other hand, it is generated by the activation of PMS by special structures such as C=O, pyridinic N, and graphitic N. The catalyst maintained high efficiency across a wide pH range (3–9), and the 0.5-SSB-3/PMS system still achieved 90.7% pollutant degradation after five reuse cycles. This study provides valuable insights into the resource utilization of sludge and the degradation of organic pollutants.