Magnetic Fe/S-modified porous carbon activates peracetic acid for emerging contaminant removal: Unveiling active sites and structure-activity relationships.

Peracetic acid (PAA) activation by carbon-based materials is a promising technology for water decontamination. However, its efficiency is hindered by the ambiguous identification of active sites and corresponding reactive species. Herein, magnetic biochar modified with Fe/S phases (Fe/S-BC) were synthesized via a facile hydrothermal-calcination method. The resulting Fe/S-BC remarkably outperforms pristine BC in sulfamethoxazole removal (∼95.5 % within 30 min) via synergistic adsorption and oxidation. This improvement is attributed to the enriched surface functional groups and promoted electrochemical performance, which collectively promotes PAA activation. Mechanistic studies revealed that sp2-hybridized carbon (sp2-C) is responsible for non-radical pathways, while CO and C = O groups are identified as the potential active sites for O2•- and R-O•, respectively. Notably, a strong correlation (R2 = 0.99) was established between the oxidation rate constants (lnkoxid) of six selected sulfonamides (SAs) and their electrophilic indexes, as supported by experimental results and density functional theory (DFT) calculations. The sustainable Fe(II)/Fe(III) redox cycling, facilitated by sulfur species, enables continuous PAA activation and reactive species generation. Accordingly, Fe/S-BC/PAA system demonstrates excellent decontamination efficiency, high robustness in complex water matrices, and exceptional reusability across multiple treatment cycles. This work highlights the critical roles of both radical and non-radical pathways, and their associated active sites in Fe/S-BC/PAA system, offering valuable insights for the development of sustainable PAA-based water treatment technologies.