Enhanced removal of sulfonamide antibiotics in water using high-performance S-nZVI/BC derived from rice straw

Sulfonamide antibiotics (SAs) are widely used in the biomedical field but pose an environmental risk as ecotoxic pollutants. Developing eco-friendly methods to degrade SAs into harmless compounds is crucial. In this work, biochar (BC) was prepared from rice straw via pyrolysis and used to support S-nZVI, thereby forming the S-nZVI/BC composites. The results show high SAs removal efficiency (up to 98.3%) at optimal Fe/C and Fe/S molar ratios of 3:1 and 50:1, respectively, with strong tolerance to coexisting ions. Furthermore, the effectiveness of S-nZVI/BC(Fe₃/C₁, Fe₅₀/S₁) sample was validated using five real wastewaters, and the results showed consistent performance, stability and reusability. Mechanistic studies revealed that S-nZVI/BC synergized with persulfate to enhance the reactivity of sulfate-free radical (SO^4-·) and Fe²⁺. The degradation pathways of SAs, involving electrophilic substitution and nucleophilic attack, were elucidated by density functional theory (DFT) calculations. These insights were instrumental in comprehending the degradation mechanism of SAs. Additionally, the degradation dynamics of ten SAs were further analyzed using quantitative structure-activity relationship (QSAR) models and principal component analysis (PCA). Hence, this work highlights the potential of S-nZVI/BC for industrial wastewater treatment, providing insights into the degradation mechanisms and pathways of SAs.