Investigation of PFAS/nPd/μZVI interactions: mechanism, performance, and nPd/μZVI reuse

Due to their persistence, toxicity, and environmental spread, PFAS have been extensively studied for removal since the early 2000s. This study investigates the interactions between nano-sized palladium-coated zero-valent iron microparticles (nPd/μZVI) and perfluorooctanoic acid (PFOA) or perfluorooctanesulfonic acid (PFOS) to examine the mechanism and evaluate the performance of these two PFAS abatement. Batch experiments were performed under anoxic conditions (1-72 h, 90 °C) using 1 g of ultrasonicated (45 Hz) slurries of nPd/μZVI and 9.29 to 485 mg L^-1 of PFAS across a pH range of 1-14. After the reaction and subsequent settling, samples of the aqueous phase were collected for pH measurement, fluoride analysis using a fluoride ion-selective electrode (F-ISE), and quantification of residual PFOA or PFOS and potential byproducts using ultra-high-performance liquid chromatography coupled with mass spectrometry (UHPLC-MS). Methanol used to wash nPd/μZVI under oxic conditions was also analyzed to differentiate between PFAS adsorption and their defluorination. The washing step enabled reuse of the nPd/μZVI, which were characterized by XRD and SEM-EDS before interaction, after interaction, and following methanol washing. PFAS sorption, governed by surface complexation and hydrophobic interactions, is the predominant PFAS abatement mechanism. It is driven by the anoxic galvanic corrosion of nPd/μZVI (AGC-nPd/μZVI), which modifies the physical and chemical conditions of the liquid phase and the surface chemistry of nPd/μZVI as a function of pH. Under the investigated conditions, a linear sorption model accurately described PFAS abatement at pH 4, where nPd/μZVI were shown to be reusable for at least 4-5 cycles without significant loss of sorption efficiency.