Zerovalent Iron-Loaded Biochar Coupled with Ball Milling for Perfluorooctanesulfonic Acid Remediation: Synergistic Capture and Mechanochemical Degradation

Per- and polyfluoroalkyl substances (PFASs), particularly perfluorooctanesulfonic acid (PFOS), are ubiquitous persistent pollutants in environmental matrices at trace concentrations, posing long-term risks to ecological safety and human health. This study developed an integrated system coupling zerovalent iron-loaded biochar (BC-ZVI) with ball milling for simultaneous PFOS capture and degradation. Under optimal conditions, BC-ZVI achieved near-complete removal of 53.8 mg·L–1 PFOS within 60 min (residue below detection limit), with similar efficiency for PFOA, GenX, PFBA, and PFBS. Synergistic electrostatic interactions, pore diffusion, and material hydrophobicity collectively govern the efficient adsorption. Subsequent ball milling degraded 99.9% adsorbed PFOS with 57.9% defluorination within 480 min. Mechanistically, Fe-mediated electron transfer reduces C–S bond dissociation energy from 366.4 to 315.9 kJ·mol–1, facilitating PFOS cleavage to generate CF3(CF2)7· radicals. These radicals predominantly undergo defluorination via the ·OH pathway (ΔG‡ = 97.93 kJ·mol–1), whereas the alternative ·H pathway is kinetically unfavorable due to a prohibitively high energy barrier (ΔG‡ = 907.28 kJ·mol–1). Notably, BC-ZVI maintained robust adsorption capacity after aerobic aging, anaerobic aging, and sulfidation, with only minor impairments to ball milling-mediated PFOS degradation. Recyclability tests demonstrated stable adsorption performance across three consecutive cycles, with a slight decline in degradation efficiency. Integrated assessment confirms that the BC-ZVI/ball milling system represents a sustainable and cost-effective strategy for PFOS remediation.