Bismuth-Sulfur Engineered Zero-Valent Iron Prioritizes Chloramphenicol-Class Antibiotics Dechlorination Over Hydrogen Evolution and Nitro Reduction

Chloramphenicol (CAP) and florfenicol (FF), as chloramphenicol-class antibiotics, often coexist in wastewater, where chlorine substituents largely determine their toxicity. Although zero-valent iron (ZVI) is a promising reductive remediation material, its poor chemoselectivity and preferential electron consumption by hydrogen evolution (HER) and nitro-reduction severely limit the detoxification of chlorinated moieties. Herein, we develop bismuth-sulfur co-intercalated ZVI (Bi-S-ZVI) to reduce CAP+FF co-contaminants, achieving enhanced nitro-reduction (22-74-fold), dechlorination (175-419-fold), and low HER. Notably, the dechlorination selectivity (defined as the ratio of FF dechlorination to CAP nitro-reduction) increased from 0.3%-2% to 39%, and Bi-S-ZVI enabled a distinct pathway where dechlorination preceded nitro-reduction in the -NO₂/-Cl co-substituted CAP molecule. Mechanistically, Bi₂S₃ and Bi⁰ are the dominant contributors to the reactivity and dechlorination selectivity of Bi-S-ZVI, respectively. Bi₂S₃ couples galvanically with Fe⁰ to generate a built-in electric field and creates Fe-S-Bi charge-transfer channels to accelerate electron transport. Bi⁰ selectively associates with ─Cl as a halogen-bond acceptor. Bi₂S₃ and Bi⁰ synergistically suppress HER by increasing surface hydrophobicity and hindering atomic hydrogen recombination, while Bi₂S₃ further disrupts the interfacial hydrogen-bonding network. This work provides a cost-effective and scalable strategy for selective reductive remediation, overcoming the reactivity-selectivity-stability trade-offs of existing iron materials.