Bypassing reductive dimerization of bottleneck PFAS intermediates via asymmetric advanced oxidation for absolute defluorination

Abstract Hydrated electron (e aq − )-based advanced reduction processes (ARPs) have been widely employed to initiate non-thermal cleavage of highly stable C—F bonds in per- and polyfluoroalkyl substances (PFAS). However, complete defluorination is rarely achieved, as downstream transformation pathways consistently stall at short-chain intermediates. In this study, the origin of this reductive arrest is elucidated. A pronounced collapse of localized electron affinity in ultra-short C2 terminal intermediates suppresses further electron injection, thereby diverting perfluorinated radicals toward self-recombination pathways that produce dimeric end products. Under vacuum ultraviolet irradiation, a coupled oxidation/reduction environment was shown to overcome this energetic limitation through an asymmetric oxidative interception pathway. Wavefunction analysis combined with Marcus-theory-based density functional theory calculations indicates that this process is governed by a highly localized orbital polarization centered on the desorbed carbon atoms of C2 intermediates. Such polarization enables near barrier-free cross-coupling with coexisting HO•, facilitating rapid capture of transient radicals before dimer formation or volatilization. This oxidative pathway redirects bottleneck intermediates toward unstable fluorinated alcohol analogues, which subsequently undergo spontaneous intramolecular ketonization, resulting in progressive fluorine elimination. To unlock chemical descriptors governing complete PFAS defluorination, a data-enhanced generative framework (VAE-ANN) was applied to more than 90 congeners. A key synergy descriptor (ŋ G/F ) was thereby established to define the optimal oxidant-to-reductant ratio required for achieving complete defluorination. This work demonstrates that complete PFAS mineralization should transcend conventional metrics, such as carbon chain length, by prioritizing the mechanistic alignment between intrinsic molecular features and extrinsic reaction conditions.