Persulfate activation by low-rank coals for sulfamethazine degradation: Structural differences modulating activation pathways

Carbon-driven persulfate (PS) activation is promising for antibiotic degradation, but conventional carbon catalysts often require thermal/acid-base modification or metal doping, suffering from low yields and high costs. Herein, we innovatively employed unmodified low-rank coals from Shengdong (LC SD ) and Sujiagou (LC SJG ) as cost-effective PS activators for sulfamethazine (SMZ) degradation. Characterizations including Raman, 13 C nuclear magnetic resonance, and electron paramagnetic resonance (EPR) revealed distinct structural-chemical features. LC SJG had more structural defects, –OH, and –COOH groups, while LC SD showed higher persistent free radical and C O group concentrations. LC SJG exhibited superior performance (99.3 % SMZ removal in 120 min) versus LC SD (84.2 %) and good tolerance to coexisting ions, indicating practical application potential. Possible degradation pathways of SMZ, as revealed by high-performance liquid chromatography-mass spectrometry, were proposed involving sulfonamide cleavage and pyrimidine ring opening. Mechanistic investigations via EPR, radical quenching, and electrochemical analysis revealed that 1 O 2 dominated SMZ degradation (59.3 %) in the LC SD /PS system via C O groups. Conversely, • OH and SO 4 •− contributed 62.7 % to degradation in the LC SJG /PS system through structural defects and –COOH groups. Overall, this study provides a novel strategy for developing low-cost, high-performance PS activators tailored for wastewater treatment.