Ultrafast carbon tetrachloride dechlorination by assembling electron and hydrogen bridges over sulfidated zero-valent iron interfaces

AbstractSulfidated zero-valent iron (S-ZVI) offers an attractive and sustainable approach for dechlorinating persistent chlorinated organics. However, it remains challenging to efficiently dechlorinate chlorinated organics with highly-symmetrical structure and extreme hydrophobicity, due to the limited contact interface and the insufficient electron/proton transfer efficiency of S-ZVI. In this study, we report a surfactant-mediated interfacial engineering strategy that achieves unprecedented carbon tetrachloride (CT) dechlorination kinetics (8.36 h−1) over S-ZVI, representing the highest reported rate constant to date. By optimizing a dual-surfactant assembly (0.08 g·L−1 HTAB + 0.03 g·L−1 Tween 80, HTTW), we demonstrate a synergistic “dual-bridging” mechanism that simultaneously enhances electron transfer and hydrogenation towards CT dechlorination. Dichloromethane (91.40 ± 0.11%) was determined as the primary product, which is the least toxic chlorinated hydrocarbon. Experimental evidence and molecular dynamics simulations elucidate that this surfactant assembly creates a tailored interfacial microenvironment, where cationic HTAB constructs an electron-transfer bridge between S-ZVI and CT, lowering C-Cl bond cleavage activation energy; while nonionic Tween 80 potentially forms a hydrogen-bond bridge, that helps to generate and stabilize reactive hydrogen (H*) for CT dechlorination via hydrogenation. The HTTW/S-ZVI system is further demonstrated to exhibit excellent reproducibility, a broad dechlorination spectrum, and remarkable efficiency for CT removal in actual groundwater. Overall, this study advances the surfactant-mediated assembly strategy to improve S-ZVI’s dechlorination efficacy, providing a technical approach for remediating chlorinated organics via bridging effects of electron or H-bonds.