Per-and polyfluoroalkyl substances (PFAS), a large class of synthesized chemicals, are persistent in nature and generally recalcitrant to conventional chemical and biological treatment. Adsorption is considered an economical and practical method for PFAS treatment. Layered double hydroxides (LDHs) represent a promising class of mineral-based adsorbents for PFAS removal because of the highly positive charge of their structural layers. In this research, the performance of two representative LDHs with varied cation compositions, namely Zn–Al and Mg–Al LDHs, were investigated and compared for the removal of perfluorinated carboxylic acids (PFCAs) with an emphasis on perfluorooctanoic acid (PFOA). Zn–Al LDH showed high efficiency for the removal of medium- and long-chain PFCAs (i.e., C ≥ 7), and performed consistently better than Mg–Al LDH. Based on detailed adsorption kinetics and isotherm studies toward PFOA, Zn–Al LDH showed higher adsorption capacity, stronger adsorption affinity, and faster kinetics than Mg–Al LDH. Presence of natural organic matter had minimal impact on PFOA removal by Zn–Al LDH, but sulfate severely inhibited PFOA adsorption. Combined results of aqueous adsorption experiments and sorbent characterization suggested that electrostatic interactions may be the primary mechanism for PFOA adsorption onto LDHs. Our results suggested that cation composition of LDHs can have significant effect on the performance for PFCA removal.

全氟和多氟烷基物质 (PFAS) 是一大类合成化学品，在性质上具有持久性，通常难以接受常规的化学和生物处理。吸附被认为是一种经济实用的全氟和多氟烷基物质处理方法。层状双氢氧化物 (LDH) 是一类很有前途的矿物基吸附剂，可用于去除 PFAS，因为它们的结构层具有高正电荷。在这项研究中，研究并比较了两种具有不同阳离子组成的代表性 LDHs，即 Zn-Al 和 Mg-Al LDHs 的性能，并比较了全氟羧酸 (PFCA) 的去除，重点是全氟辛酸 (PFOA)。Zn-Al LDH 在去除中链和长链 PFCA（即 C≥7）方面表现出很高的效率，并且始终优于 Mg-Al LDH。基于对 PFOA 的详细吸附动力学和等温线研究，Zn-Al LDH 表现出比 Mg-Al LDH 更高的吸附能力、更强的吸附亲和力和更快的动力学。天然有机物的存在对 Zn-Al LDH 去除 PFOA 的影响很小，但硫酸盐严重抑制了 PFOA 的吸附。水性吸附实验和吸附剂表征的综合结果表明，静电相互作用可能是 PFOA 吸附到 LDH 上的主要机制。我们的结果表明，LDHs 的阳离子组成对 PFCA 去除性能有显着影响。天然有机物的存在对 Zn-Al LDH 去除 PFOA 的影响很小，但硫酸盐严重抑制了 PFOA 的吸附。水性吸附实验和吸附剂表征的综合结果表明，静电相互作用可能是 PFOA 吸附到 LDH 上的主要机制。我们的结果表明，LDHs 的阳离子组成对 PFCA 去除性能有显着影响。天然有机物的存在对 Zn-Al LDH 去除 PFOA 的影响很小，但硫酸盐严重抑制了 PFOA 的吸附。水性吸附实验和吸附剂表征的综合结果表明，静电相互作用可能是 PFOA 吸附到 LDH 上的主要机制。我们的结果表明，LDHs 的阳离子组成对 PFCA 去除性能有显着影响。