Highly efficient electrochemical oxidation of hexafluoropropylene oxide homologues at a boron-doped diamond anode

Abstract

As substitutes for perfluoroalkyl substances (PFASs), hexafluoropropylene oxide (HFPO) homologues are still environmentally problematic for their issues in toxicity, bioaccumulation, and long-distance mobility, which urges efficient removal technologies and in-depth mechanistic studies. Herein, we present the systematic optimizations on the electrochemical oxidation of 100 mg L−1 HFPO dimer acid (HFPO-DA) at a boron-doped diamond anode (3.6 V, 100 mM Na2SO4, pH 7.0), which exhibits a powerful mineralization capacity over 97% within 210 min of operation and is highly tolerant to various environmental factors. Under the optimized conditions, the structure-reactivity relationship has been analyzed by comparing six kinds of PFASs, proving that the increasing numbers of ether bonds in the HFPO homologues favor their removal and defluorination processes. Density functional theory (DFT) calculations further indicate that the facile, water-assisted cleavage of the ether bonds in the HFPO homologues can significantly reduce the energy barriers and shorten the "-CF2" unzipping degradation cycles, which is different from the conventionally proposed mechanism for degrading PFASs. Our findings demonstrate the promising application of electrochemical oxidation in the efficient removal of PFAS substitutes and offer new mechanistic insights for designing environment-friendly F-based chemicals.