Hexafluoropropylene oxide dimer acid
(HFPO-DA, trade name GenX)
is a perfluoroalkyl ether carboxylic acid (PFECA) that has been detected
in watersheds around the world. Similar to other per- and polyfluoroalkyl
substances (PFASs), few processes are able to break HFPO-DA’s
persistent carbon–fluorine bonds. This study provides both
experimental and computational lines of evidence for HFPO-DA mineralization
during electrochemical oxidation at a boron-doped diamond anode with
a low potential for the generation of stable organofluorine intermediates.
Our density functional theory calculations consider the major operative
mechanism, direct electron transfer, throughout the entire pathway.
Initial oxidative attack does not break the ether bond, but leads
to stepwise mineralization of the acidic side chain. Our mechanistic
investigations reveal that hydroxyl radicals are unreactive toward
HFPO-DA, while electrochemically activated sulfate facilitates its
oxidation. Furthermore, we demonstrate that an NF90 membrane is capable
of removing 99.5% of HFPO-DA from contaminated water. Electrochemical
treatment of the nanofiltration rejectate is shown to reduce both
energy and electrode costs by more than 1 order of magnitude compared
to direct electrochemical treatment of the raw water. Overall, a nanofiltration–electrochemical
oxidation treatment train is a sustainable destructive approach for
the cost-effective elimination of HFPO-DA and other PFASs from contaminated
water.
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