Zhang Chi, Zhou Zhiyu, Xi Mengning, Ma Haozhe, Qin Junhao, Jia Hanzhong
College of Natural Resources and Environment, Northwest A & F University, Xianyang 712100, China.
Key Laboratory of Low-Carbon Green Agriculture in Northwestern China, Ministry of Agriculture and Rural Affairs, Xianyang 712100, China.
Eco Environ Health. 2024 Sep 11;4(1):100122. doi: 10.1016/j.eehl.2024.08.004. eCollection 2025 Mar.
The interactions of nanoplastics (NPs) with natural organic matters (NOMs) dominate the environmental fate of both substances and the organic carbon cycle. Their binding and aggregation mechanisms at the molecular level remain elusive due to the high structural complexity of NOMs and aged NPs. Molecular modeling was used to understand the detailed dynamic interaction mechanism between NOMs and NPs. Advanced humic acid models were used, and three types of NPs, i.e., polyethylene (PE), polyvinyl chloride (PVC), and polystyrene (PS), were investigated. Molecular dynamics (MD) simulations revealed the geometrical change of the spontaneous formation of NOMs-NPs supramolecular assemblies. The results showed that pristine NPs initially tend to aggregate homogeneously due to their hydrophobic nature, and then NOM fragments are bound to the formed NP aggregates mainly by vdW interaction. Homo- and hetero-aggregation between NOMs and aged NPs occur simultaneously through various mechanisms, including intermolecular forces and Ca bridging effect, eventually resulting in a mixture of supramolecular structures. Density functional theory calculations were employed to characterize the surface properties and reactivity of the NP monomers. The molecular polarity indices for unaged PE, PS, and PVC were 3.1, 8.5, and 22.2 kcal/mol, respectively, which increased to 43.2, 51.6, and 42.2 kcal/mol for aged NPs, respectively, indicating the increase in polarity after aging. The vdW and electrostatic potentials of NP monomers were visualized. These results clarified the fundamental aggregation processes, and mechanisms between NPs and NOMs, providing a complete molecular picture of the interactions of nanoparticles in the natural aquatic environment.
纳米塑料（NPs）与天然有机物（NOMs）的相互作用主导了这两种物质的环境归宿以及有机碳循环。由于NOMs和老化纳米塑料的高度结构复杂性，它们在分子水平上的结合和聚集机制仍然难以捉摸。分子建模被用于理解NOMs与纳米塑料之间详细的动态相互作用机制。使用了先进的腐殖酸模型，并研究了三种类型的纳米塑料，即聚乙烯（PE）、聚氯乙烯（PVC）和聚苯乙烯（PS）。分子动力学（MD）模拟揭示了NOMs - 纳米塑料超分子聚集体自发形成的几何变化。结果表明，原始纳米塑料最初由于其疏水性质倾向于均匀聚集，然后NOM片段主要通过范德华相互作用与形成的纳米塑料聚集体结合。NOMs与老化纳米塑料之间的同聚和异聚通过各种机制同时发生，包括分子间力和钙桥接效应，最终导致超分子结构的混合。采用密度泛函理论计算来表征纳米塑料单体的表面性质和反应活性。未老化的PE、PS和PVC的分子极性指数分别为3.1、8.5和22.2千卡/摩尔，对于老化的纳米塑料分别增加到43.2、51.6和42.2千卡/摩尔，表明老化后极性增加。可视化了纳米塑料单体的范德华和静电势。这些结果阐明了纳米塑料与NOMs之间的基本聚集过程和机制，提供了天然水生环境中纳米颗粒相互作用的完整分子图景。
