Enhanced electrochemical degradation of perfluorooctanoic acid by ligand-bridged Pt at Pt anodes.

A new mechanism for the electro-oxidation (EO) degradation of perfluorooctanoic acid (PFOA) by Pt anode was reported. Using bridge-based ligand anions (SCN, Cl and N) as electrolytes, the degradation effect of PFOA by Pt-EO system was significant. Characterization of the Pt anode, the detection and addition of dissolved platinum ions, and the comparison of Pt with DSA anodes determined that the Pt- ligand complexes resulting from the specific binding of anodically dissolved Pt with ligand ions and CFCOO ((CF-COO)Pt-L, L = SCN, Cl and N) on the electrode surface played a decisive role in the degradation of PFOA. Density functional theory (DFT) calculations showed that inside (CF-COO)Pt-L complexes, the electron density of the perfluorocarbon chain (including the F atom) compensated toward the carboxyl group and electrons in the PFOA ion transferred to the Pt-Cl. Moreover, the (CF-COO)Pt-Cl, as a whole, was calculated to migrate electrons toward the Pt anode, leading to the formation of PFOA radical (CF-COO•). Finally, with the detection of a series of short chain homologues, the CF-unzipping degradation pathway of PFOA was proposed. The newly developed Pt-EO system is not affected by water quality conditions and can directly degrade alcohol eluent of PFOA, which has great potential for treating industrial wastewater contaminated with PFOA.