Core-shell nZVI@NC as a scalable PRB filler for remediating PFOA-contaminated groundwater via synergistic adsorption

Perfluorooctanoic acid (PFOA) poses a significant and persistent threat to groundwater due to its stability, high mobility, and carcinogenicity. Conventional permeable reactive barrier (PRB) fillers, like nano zero-valent iron (nZVI), face challenges including nanoparticle aggregation and passivation. To overcome these limitations, this study developed nitrogen-doped carbon-stabilized nZVI (nZVI@NC) using a scalable, solvent-free method combining mechanochemical ball-milling and pyrolysis. The synthesized core-shell nZVI@NC material effectively encapsulates nZVI within graphitic carbon, significantly improving its dispersion and reactivity (with an average crystallite size of 24.78 nm). A concentration of 100 mg/L of nZVI@NC adsorbed 83.5 % of PFOA within a 2-h timeframe, and the isotherms revealed an outstanding PFOA uptake capacity of 162 mg/g. Column experiments confirmed practical efficacy: using 50 mg nZVI@NC achieved complete PFOA removal (initial influent: 0.1 mg/L, Darcy velocity: 0.81 m/day) with no breakthrough for the first 1188 mL. Furthermore, a removal efficiency of 61.3 % was sustained in actual groundwater. Mechanistic studies (XPS, SEM-EDS, AIMD simulations) revealed a biphasic adsorption process: an initial rapid phase driven by physicochemical interactions, followed by a diffusion phase governed by pore embedding. This work establishes nZVI@NC as an efficient, scalable, and high-performance PRB filler for sustainable in situ remediation of PFOA-contaminated groundwater.