The study investigated molecular mechanisms of per- and polyfluoroalkyl substances (PFAS) on a surfactant modified clay (SMC), which rivals or exceeds the performance of granular activated carbon in removing long-chain PFAS from contaminated water. The adsorption isotherms of four anionic and one neutral PFAS from 1 × 10^–9 to 1 × 10^–5 mol/L were measured to be piecewise, accompanied by the expansion of the SMC interlayer. Based on the spatial distribution of perfluorocarboxylic acid (PFOA) on SMC at the submicron scale, achieved by synchrotron-based scanning transmission X-ray microscopy (STXM) coupled with X-ray absorption near-edge structure spectroscopy (XANES), PFOA molecules were confirmed to enter the interlayer space of SMC and could form charge-charge interaction with the intercalants (quaternary ammonia cations). Revealed by the all-atom molecular dynamics (MD) simulation and density functional theory-based quantum calculations, the interactions between the positively charged surfactant and representative PFAS include charge-charge, charge-dipole, and dipole-dipole interactions. The adsorption mechanisms vary from one PFAS structure to another in terms of adsorption energy and spatial arrangement. Those interactions overcome the interaction between PFAS and water, allowing PFAS to be retained in the SMC's interlayer space. The study provides fundamental insights into how PFAS interact with clay-based materials, supporting the use of the materials for PFAS treatment and remediation.

该研究调查了表面活性剂改性粘土 (SMC) 上全氟和多氟烷基物质 (PFAS) 的分子机制，其在去除受污染水中长链 PFAS 方面的性能可与颗粒活性炭相媲美或超过其性能。四种阴离子和一种中性 PFAS 的吸附等温线从 1 × 10 ^–9到 1 × 10 ^–5 mol/L 被测量为分段的，伴随着 SMC 夹层的膨胀。基于全氟羧酸 (PFOA) 在亚微米尺度上的 SMC 空间分布，通过基于同步加速器的扫描透射 X 射线显微镜 (STXM) 结合 X 射线吸收近边结构光谱 (XANES) 实现，PFOA 分子是确认进入SMC的层间空间并可以与嵌入剂（季铵阳离子）形成电荷 - 电荷相互作用。通过全原子分子动力学 (MD) 模拟和基于密度泛函理论的量子计算揭示，带正电荷的表面活性剂与代表性 PFAS 之间的相互作用包括电荷-电荷、电荷-偶极子和偶极子-偶极子相互作用。在吸附能和空间排列方面，吸附机制从一种 PFAS 结构到另一种结构不同。这些相互作用克服了 PFAS 和水之间的相互作用，使 PFAS 能够保留在 SMC 的层间空间中。该研究提供了关于 PFAS 如何与粘土基材料相互作用的基本见解，支持使用这些材料进行 PFAS 处理和修复。