Transient Kinetics of Short-Chain Perfluoroalkyl Sulfonate with Radiolytic Reducing Species

The role of the short-lived hydrated electron (eaq–) has recently begun to be appreciated in per- and polyfluoroalkyl substances (PFAS) remediations; nevertheless, few studies to date focused on short-chain PFAS, and their effective defluorination has been limited by an insufficient mechanistic understanding, which starts with the elusive initial step of eaq– reduction. Herein, this study uses pulse radiolysis to clarify the rate constant of the eaq– reaction with a highly recalcitrant short-chain PFAS, perfluorobutanesulfonate (PFBS, C4F9SO3–), and verify chain length dependence. The measured values contradict earlier results from laser photolysis but reconcile with the apparent degradation profiles and theoretical predictions. Besides, we first disclose radiolytic carbon dioxide radicals (CO2–•) to defluorinate PFBS with an initial reaction constant of 4.8 × 107 M–1 s–1, and it achieves selective cleavage on the more obstinate C–F bond than eaq– even under a neutral condition. Quantitative 60Co γ-ray irradiation experiments further show that initial reduction occurs through a defluorination pathway rather than a desulfurization pathway, and the redox potential of PFBS exceeds −2.0 eV. This radiolytic study addressed the long-standing mechanistic contradictions regarding short-chain PFAS degradation and suggested ionizing radiation as a versatile and direct treatment technique.