Multiple interactions steered high affinity toward PFAS on ultrathin layered rare-earth hydroxide nanosheets: Remediation performance and molecular-level insights

Abstract

The global occurrence of per- and polyfluoroalkyl substances (PFAS) in aquatic systems has raised concerns about their adverse effects on ecosystems and human health. Adsorption is a promising technique for the remediation of PFAS, yet effective adsorbents with rapid uptake kinetics and high adsorption capacity are still in high demand, and molecular-level understanding of the interfacial adsorption mechanisms is lacking. In this study, we developed a superior layered rare-earth hydroxide (LRH) adsorbent, ultrathin Y2(OH)4.86Cl1.44·1·07H2O (namely YOHCl) nanosheets, to achieve the effective removal of perfluorooctanoic acid (PFOA). YOHCl nanosheets exhibited ultra-high adsorption capacity toward PFOA (up to 957.1 mg/g), which is 1.9 times and 9.3 times higher than the state-of-the-art layered double hydroxides (MgAl-LDH) and benchmark granular activated carbon (GAC) under the same conditions, respectively. Furthermore, YOHCl nanosheets pose stable performance on the removal of PFOA under various water matrices with robust reusability. We also developed YOHCl-based continuous-flow column, demonstrating its promise in simultaneously removing multiple PFAS with wide range of chain lengths at environmentally relevant concentrations. With the molecular-level investigations, we have revealed that multi-mechanism, including ion exchange, electrostatic attraction and bidentate/bridging coordination, contributed to the strong PFOA-YOHCl affinity, leading to the ultra-high adsorption capacity of PFOA. We have provided emerging LRHs-based adsorbents for the effective remediation of PFAS with molecular-level insights on the interfacial mechanisms.