Enhanced persulfate activation for sulfadiazine degradation by N, S self-doped biochar from sludge and sulfonated lignin: Emphasizing the roles of graphitic nitrogen and thiophene sulfur

Biochar derived from sludge is recognized for its sustainable and cost-effective role in advanced oxidation processes, yet its restricted catalytic capacity poses significant challenges. In this work, nitrogen (8.43 at%) and sulfur (1.39 at%) co-doped biochar (ML-SDBC) featuring a large surface area of 161.14 m2/g was synthesized by the pyrolysis of sewage sludge and sulfonated lignin without external dopants. In the synthesis of ML-SDBC, graphitic nitrogen and thiophene sulfur were efficiently integsrated into the carbon framework. Furthermore, the resulting biochar notably outperformed sludge-derived biochar (SDBC) in activating peroxymonosulfate (PMS) for sulfadiazine (SDZ) degradation, achieving a 31.9% higher removal rate within 120 min and exhibiting a rate constant (kobs) of 1.73×10-2 min-1, effectively tripling the efficiency compared to that of SDBC-driven processes. The degradation rate consistently exceeded 85% across a wide pH range of 3-9. Mechanistic analysis exhibited that degradation processes involved radical and non-radical pathways, with 1O2 playing a prominent role. Furthermore, density functional theory (DFT) calculations revealed that the catalytic potential in ML-SDBC would benefit from the synergistic interaction between graphitic nitrogen and thiophene sulfur. This study presents a novel synthesis of heteroatom-doped biochar from waste, offering a sustainable solution to antibiotic pollution and waste management challenges.