Zhang Fan, Wu Yingxin, Ye Quanyun, Wang Jinxi, Wu Qiong, Zhou Lingli, Wu Wencheng, Xie Shuting
School of Earth Science and Engineering, Hebei University of Engineering, Handan, 056038, PR China; South China Institute of Environmental Sciences, Ministry of Ecology and Environment, Guangzhou, 510655, PR China.
South China Institute of Environmental Sciences, Ministry of Ecology and Environment, Guangzhou, 510655, PR China.
Environ Res. 2025 Oct 15;283:122101. doi: 10.1016/j.envres.2025.122101. Epub 2025 Jun 7.
Short-chain chlorinated paraffins (SCCPs) have raised global concerns owing to their toxicity and bioaccumulation as persistent organic pollutants. Although zerovalent iron (ZVI) is promising in SCCP dechlorinating, the selectivity mechanisms are scarcely investigated, which hinders the understandings on the environmental and toxicological profiles of the dechlorinated products. This study investigated the homolog- and site-selective dechlorination of C-SCCPs through kinetic experiments and density functional theory (DFT) analysis. The dechlorination efficiency change with ZVI dosage (10-40 g L) was nonmonotonic, with the efficiency peaking at 20 g L, possibly due to the higher Fe abundance on ZVI surface. The dechlorination priority followed CCl > CCl > CCl > CCl > CCl > CCl, which was driven by both SCCP adsorption and reactivity. The accumulation of CCl as the dechlorinated products of CCl led to the anomalous phenomenon of CCl > CCl. In particular, higher chlorinated homologs showed stronger affinity to ZVI; meanwhile, DFT calculations demonstrated that chlorine substitution patterns altered the molecular softness and steric accessibility. The enhanced reactivity of homologs with even chlorine numbers was explained by the symmetric lowest unoccupied molecular orbital (LUMO). Intramolecular crowding shifted the dechlorination hotspots from peripheral C(3)/C(10) to central C(6)/C(7) in CCl, where the reduced steric hindrance maximized the reactivity. The number of chlorine atoms and the substitution positions jointly determined the LUMO distribution of SCCPs and the spatial effect to regulate their properties. Overall, these findings elucidate the molecular-scale determinants of SCCP dechlorination selectivity and provide a mechanistic framework for optimizing ZVI-based remediation.
短链氯化石蜡（SCCPs）因其作为持久性有机污染物的毒性和生物累积性而引起了全球关注。尽管零价铁（ZVI）在SCCP脱氯方面具有潜力，但对其选择性机制的研究却很少，这阻碍了人们对脱氯产物的环境和毒理学特征的理解。本研究通过动力学实验和密度泛函理论（DFT）分析，研究了碳链氯化石蜡（C-SCCPs）的同系物选择性和位点选择性脱氯。脱氯效率随ZVI剂量（10-40 g L）的变化并非单调，在20 g L时效率达到峰值，这可能是由于ZVI表面较高的铁含量所致。脱氯优先级遵循CCl > CCl > CCl > CCl > CCl > CCl，这是由SCCP的吸附和反应性共同驱动的。作为CCl脱氯产物的CCl的积累导致了CCl > CCl的异常现象。特别是，高氯代同系物对ZVI表现出更强的亲和力；同时，DFT计算表明，氯取代模式改变了分子的柔软性和空间可及性。具有偶数氯原子的同系物反应性增强可以用对称的最低未占分子轨道（LUMO）来解释。分子内拥挤使CCl中脱氯热点从外围的C(3)/C(10)转移到中心的C(6)/C(7)，在那里空间位阻的降低使反应性最大化。氯原子的数量和取代位置共同决定了SCCPs的LUMO分布和调节其性质的空间效应。总体而言，这些发现阐明了SCCP脱氯选择性的分子尺度决定因素，并为优化基于ZVI的修复提供了一个机理框架。
