Exploration of PFAS degradation over lower titanium suboxides: Ti6O11 case.

Herein, the Magneli phase is synthesised and applied to the electrochemical oxidation of PFAS. Rietveld refinement, together with FTIR and Raman spectroscopy, confirmed Ti6O11 as the predominant phase. EPR spectroscopy revealed the formation of SO4⦁-, OH⦁, and O2⦁- radicals at the Ti6O11 adlayer, with the additional appearance of spin-trap adducts with carbon, attributed to PFAS degradation products. Quenching experiments point to SO4⦁- driving the initial step of the degradation, with subsequent degradation involving concerted action with the abundant OH⦁, as confirmed by UPLC-MS/MS, with 94% degradation of PFOS and 67% of PFOA. Degradation was monitored under a potentiostatic regime, where electric energy per order was 0.8 kWh m-3 and 1.7 kWh m-3 for PFOS and PFOA, respectively, indicating easier PFOS degradation. Theoretical calculations predicted a 0.69 eV barrier for the decarboxylation of PFOA, after the initial radical formation, while PFOS degradation proceeds barrierlessly. Degradation efficiency in the river water with mixed PFAS panel (PFCAs C4-C14, C16, C18, and PFSAs C4-C10, C12) was excellent (∼95%) for long-chain PFAS, while lowered to ∼40% for PFSAs (C4-C5) and ∼20% for PFCAs (C7-C8). Ti6O11 presents an alternative to the widely studied Ti4O7 for the electrochemical oxidation of PFAS.