Chen Zhixin, Hu Liming
State Key Laboratory of Hydro-Science and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China.
Materials (Basel). 2022 Jul 23;15(15):5120. doi: 10.3390/ma15155120.
Naphthalene, as one of the representative polycyclic aromatic hydrocarbons, widely exists in contaminated sites and is a potential threat to human health due to its high mobility in soil. The interaction between naphthalene and clay minerals is of great significance to the environmental behavior of naphthalene and the design of remediation technology. In this study, montmorillonite and kaolinite were selected as representative clay minerals. Naphthalene adsorption behavior on mineral surfaces and water-wet kaolinite surfaces was investigated using molecular dynamics (MD) simulation. The interaction energy was calculated to represent the interaction between naphthalene and soil fractions, and the relative concentration and density distribution of naphthalene was analyzed to describe the distribution of naphthalene on the clay surfaces. The self-diffusion coefficient of naphthalene was obtained to represent its mobility under different water content. The electron density calculation was performed to reveal the different adsorption behavior of naphthalene on different surfaces of kaolinite. The simulation results show that montmorillonite had a stronger interaction with naphthalene due to larger electrostatic interaction energy compared to kaolinite, and naphthalene distributed more intensively on the montmorillonite surface. With regards to kaolinite, naphthalene tended to be absorbed on the alumina octahedral surface rather than the silicon tetrahedral surface due to the weak hydron bond interaction. The results indicate that water impeded the adsorption of naphthalene, and the optimal initial thickness of water film, which was 10 Å, was put forward for the application of thermal remediation technology. Furthermore, the average interaction energies between water and mineral surfaces largely depended on the water content, and the competitive adsorption between water and naphthalene only occurred under absorbed and bound water conditions. Overall, the knowledge of naphthalene-soil fractions interaction gained in this study is critical to the understanding of the environmental behavior of naphthalene and the reference for remediation technology.
萘作为代表性的多环芳烃之一，广泛存在于受污染场地，因其在土壤中具有高迁移性，对人类健康构成潜在威胁。萘与黏土矿物之间的相互作用对于萘的环境行为及修复技术设计具有重要意义。本研究选取蒙脱石和高岭土作为代表性黏土矿物，采用分子动力学（MD）模拟研究萘在矿物表面及水湿高岭土表面的吸附行为。通过计算相互作用能来表征萘与土壤组分间的相互作用，分析萘的相对浓度和密度分布以描述其在黏土表面的分布情况。获取萘的自扩散系数以表征其在不同含水量下的迁移性。进行电子密度计算以揭示萘在高岭土不同表面的不同吸附行为。模拟结果表明，与高岭土相比，蒙脱石因具有更大的静电相互作用能而与萘的相互作用更强，萘在蒙脱石表面分布更密集。对于高岭土，由于氢键相互作用较弱，萘倾向于吸附在氧化铝八面体表面而非硅四面体表面。结果表明，水会阻碍萘的吸附，并提出了热修复技术应用的最佳水膜初始厚度为10 Å。此外，水与矿物表面之间的平均相互作用能很大程度上取决于含水量，且水与萘之间的竞争吸附仅在吸附水和结合水条件下发生。总体而言，本研究获得的萘与土壤组分相互作用的知识对于理解萘的环境行为及修复技术参考至关重要。
