Unlocking Oxidative Potential of Ferrate (VI): Nanoscale Zerovalent Iron Loaded Sludge Biochar Mediated Nonradical Sulfonamides Degradation via Valence Conversion

The novel mechanism of intramolecular redox equilibration between nanoscale zerovalent iron (n-ZVI) and ferrate (VI) [Fe (VI)] facilitates the formation of highly reactive intermediate-valence metal species. In this study, sludge biochar (SBC) was used as a carrier to form n-ZVI@SBC, which significantly improved the activation of Fe (VI). Comprehensive characterizations confirmed the successful loading of n-ZVI onto SBC via liquid-phase reduction. The optimized Fe (VI)/n-ZVI@SBC system achieved high removal efficiency for sulfamethoxazole (SMX) (91.30%) and broad-spectrum degradation of sulfonamides (SAs) (67.48–99.60%) within 3 min. However, the system showed limited tolerance to high concentrations of HCO3–, CO32–, and humic acid due to hydrolysis and competitive effects. Mechanistic studies revealed that high-valent iron species [Fe (V)/Fe (IV)] dominated the degradation process, with electron transfer also playing a role. The –OH groups and n-ZVI loading sites were identified as key regions for adsorption and activation. This system demonstrated robust performance in natural water matrices and enhanced flocculation through Fe (VI) decomposition products. Cyclic and fixed-bed experiments confirmed its reliability and sustainability. This study presents an innovative strategy to enhance Fe (VI) oxidation properties, offering a promising solution for remediation of antibiotic-contaminated waters.