Enhanced sulfamethoxazole degradation by peroxymonosulfate activation with sulfide-modified microscale zero-valent iron (S-mFe0): Performance, mechanisms, and the role of sulfur species

Sulfide-modified microscale zero-valent iron (S-mFe(0)) was applied to activate peroxymonosulfate (PMS) to degrade sulfamethoxazole (SMX), a typical sulfonamide bacteriostatic antibiotic. In this work, the effects of S/Fe molar ratio, S-mFe(0) dosage, PMS dosage, different initial pH value, dissolved oxygen, SMX concentration and inorganic ions on SMX removal by S-mFe(0)/PMS system were investigated, respectively. Besides, the role of sulfur species (including the FeS, SO32-, S2-) was studied. In contrast to mFe(0)/PMS system, the removal efficiency of SMX obtained by S-mFe(0)/PMS system was increased by 29.4%. Radical quenching and Electron Paramagnetic Resonance spectroscope (EPR) tests identified that both center dot OH and SO4 center dot- were committed to degrading SMX, and SO4 center dot- was proven to be the dominant one. The electrochemical analysis of S-mFe(0) and bare mFe(0), implying a better electron transfer ability of S-mFe(0) due to the formation of FeS. Furthermore, the activation of S2- for PMS could be ruled out by EPR tests results. Conversely, SO32- could effectively activate PMS to generate reactive oxygen species (ROS). The catalytic mechanisms of S-mFe(0)/PMS system were clarified by SEM-EDS, XRD, XPS, radical quenching and EPR tests. Based on the detected intermediates via LC-TOF-MS/MS, the degradation pathways of SMX by S-mFe(0)/PMS system were proposed. Overall, the work suggests that S-mFe(0)/PMS system has a good potential for the elimination of micropollutants in the aquatic environment.