Zero-valent iron and biochar composite with high specific surface area via K₂FeO₄ fabrication enhances sulfadiazine removal by persulfate activation

Zero-valent iron and biochar composite (ZVI/BC) is a prospective catalyst for activating persulfate and specific surface area (SSA) of ZVI/BC is one of the most important factors affecting its efficacy in the removal of environmental contaminants. However, the green fabrication of ZVI/BC with large SSA remains a challenge. In this study, ZVI/BC with a highly porous structure and large SSA fabricated by co-pyrolysis of K₂FeO₄ and bamboo was prepared and characterized. The large SSA stemmed from the catalytic and corrosive functions of K and the oxidation of K₂FeO₄ onto bamboo. ZVI/BC fabricated with 0.05 mol/L K₂FeO₄ (BC-Fe_0.05) showed optimal sulfadiazine (SDZ) removal performance in the peroxydisulfate (PDS) activation system with complete removal after 10 min, as it showed the highest adsorptive ability of SDZ. Moreover, BC-Fe_0.05 was able to remain stable after four cycles or 80 days of storage. Higher temperature, lower pH, and Cl⁻ were beneficial to SDZ removal efficiency, whereas CO₃^2– and HPO₄²⁻ had inhibitory effects. Non-radical species (¹O₂) and radical species (SO₄^[rad]−, [rad]OH, and O₂^[rad]−) both contributed to SDZ degradation, and ¹O₂ was the most important reactive oxygen species. Four degradation pathways were proposed based on ten identified intermediates. Potential eco-toxicity analysis by ECOSAR suggested that most intermediates were less toxic than their parent compound. Overall, this study describes a green fabrication method for ZVI/BC with large SSA using K₂FeO₄ as the iron precursor. Generally, ZVI/BC with large SSA is an effective catalyst for activating persulfate to degrade antibiotics.