Iron-sulfur functionalization reconstructs the interfacial water on biochar to promote persulfate activation and sulfadiazine degradation.

Abstract

Efficient persulfate (PS) activation by biochar is often limited by sluggish interfacial electron transfer and inefficient oxidant utilization. Herein, sugarcane bagasse was converted into Fe-S functionalized biochar (Fe-S-BC) through impregnation-assisted pyrolysis. The optimized Fe-S-BC900/PS system achieved nearly complete sulfadiazine (SDZ) removal after 60 min, with a pseudo-first-order rate constant of 0.0645 min-1, 5.7-fold higher than that of Fe-BC900/PS. Fe-S functionalization generated mixed iron sulfide/oxide phases, improved charge-transfer characteristics, and altered surface Fe redox states. Radical and non-radical pathways coexisted, with hydroxyl radical (OH) and singlet oxygen (1O2) dominating SDZ degradation. Interfacial characterization further showed that Fe-S functionalization transformed the surface from hydrophobic to superhydrophilic and reorganized the interfacial hydrogen-bonding network, creating a favorable hydration microenvironment for reactant accessibility and interfacial interactions·H2O/D2O isotope experiments indicated that proton transfer involving water was unlikely to be rate determining. Density functional theory calculations further supported enhanced PS adsorption and O-O bond elongation at representative Fe-S sites. These results highlight the coupled contributions of Fe-S-containing active structures and interfacial hydration to efficient PS activation, providing a promising strategy for designing biomass-derived catalysts for water treatment.

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