Selective perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) adsorption by nanoscale zero-valent iron (nZVI): performance and mechanisms

Abstract

Per- and polyfluoroalkyl substances (PFAS) have raised significant concerns due to their persistence and harmfulness to human beings and the environment. This paper investigated the adsorption behavior of nanoscale zero-valent iron (nZVI) for two representative PFAS including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). TEM with elemental mapping illustrated the presence of fluorine at the nZVI interface after adsorption, providing visualized confirmation of PFOA/PFOS adsorption. The adsorption processes of PFOA and PFOS reached equilibrium within 1 h with maximum adsorption capacities of 17.63 mg g⁻¹ and 256.24 mg g⁻¹, respectively. Both the Tafel curve and chronoamperometry demonstrated the occurrence of electron transfer during the adsorption process of PFOA/PFOS. Due to additional iron–sulfur interactions between nZVI and PFOS, the adsorption capacity for PFOS was significantly higher than that for PFOA. DFT calculations supported that PFOS had higher adsorption energy towards Fe(0) than PFOA. The presence of oxygen promoted the nZVI oxidation, leading to desorption of both PFOA and PFOS from the adsorbent interface. This research underscores the use of nZVI as a potential emergency treatment of PFAS contamination, offering valuable insights into its adsorption behavior for environmental remediation of PFAS.