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<p>Radio-frequency (RF) atmospheric-pressure plasma jets (APPJs) provide a non-equilibrium source of reactive species, electrons, and VUV/UV radiation for plasma-liquid interfacial chemistry. Here, 10&#xa0;mg L⁻¹ perfluorooctanoic acid (PFOA) was treated in a 13.5 mL recirculating flow-through reactor coupled to an RF argon APPJ operating at 13.56&#xa0;MHz. Langmuir surface excess data indicated significant PFOA accumulation (Γ/Γₘₐₓ &gt; 40%) at the plasma-liquid interface, such that degradation was controlled primarily by the interfacial reactive-species flux rather than bulk hydrodynamics; accordingly, a tenfold increase in liquid recirculation rate did not measurably change degradation or defluorination kinetics. In contrast, discharge power strongly affected defluorination selectivity: increasing power from 45 to 60&#xa0;W only moderately increased the PFOA degradation rate constant by 35% but raised the net fluoride yield from 61 to 66% to 80–81% within 180&#xa0;min, revealing that parent removal and mineralization are mechanistically decoupled. The higher-power condition is consistent with an increased flux of plasma-generated reactive species to the interface and enhanced secondary conversion of less surface-active, bulk-partitioned fluorinated intermediates. Fluorine mass balance, byproduct evolution, scavenger experiments, and gas-composition effects support three coupled pathways: direct interfacial defluorination, stepwise chain shortening, and late-stage radical-mediated mineralization of partially transformed organofluorine intermediates that accumulate in the bulk liquid phase. These results identify early interfacial energy deposition as a key determinant of the extent of defluorination and have implications for the design principles of plasma reactors intended to treat PFAS-containing waste streams across a range of concentrations and matrices.</p>

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Mechanistic Insights into Plasma-Liquid Interfacial Degradation of Perfluorooctanoic Acid (PFOA) in an Argon RF Plasma Jet

  • 期刊论文

  • 发表日期：

    2026年7月31日

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  • Md Akibur Rahman,
  • Thomas M. Holsen,
  • Selma Mededovic Thagard

摘要

Radio-frequency (RF) atmospheric-pressure plasma jets (APPJs) provide a non-equilibrium source of reactive species, electrons, and VUV/UV radiation for plasma-liquid interfacial chemistry. Here, 10 mg L⁻¹ perfluorooctanoic acid (PFOA) was treated in a 13.5 mL recirculating flow-through reactor coupled to an RF argon APPJ operating at 13.56 MHz. Langmuir surface excess data indicated significant PFOA accumulation (Γ/Γₘₐₓ > 40%) at the plasma-liquid interface, such that degradation was controlled primarily by the interfacial reactive-species flux rather than bulk hydrodynamics; accordingly, a tenfold increase in liquid recirculation rate did not measurably change degradation or defluorination kinetics. In contrast, discharge power strongly affected defluorination selectivity: increasing power from 45 to 60 W only moderately increased the PFOA degradation rate constant by 35% but raised the net fluoride yield from 61 to 66% to 80–81% within 180 min, revealing that parent removal and mineralization are mechanistically decoupled. The higher-power condition is consistent with an increased flux of plasma-generated reactive species to the interface and enhanced secondary conversion of less surface-active, bulk-partitioned fluorinated intermediates. Fluorine mass balance, byproduct evolution, scavenger experiments, and gas-composition effects support three coupled pathways: direct interfacial defluorination, stepwise chain shortening, and late-stage radical-mediated mineralization of partially transformed organofluorine intermediates that accumulate in the bulk liquid phase. These results identify early interfacial energy deposition as a key determinant of the extent of defluorination and have implications for the design principles of plasma reactors intended to treat PFAS-containing waste streams across a range of concentrations and matrices.