Degradation of perfluorinated compounds on a boron-doped diamond electrode

Perfluorinated compounds (PFCs) are persistent in environments due to the high energy of CF bond. Electrochemical oxidation of seven PFCs in aqueous solution on a boron doped diamond (BDD) anode was studied in this study. The kinetics results show that the pseudo-first order kinetic constants of perfluoroalkyl carboxyates and sulfonates increased with the increase of carbon chain length. PFCs decomposition began with a direct one electron transfer from carboxyl or sulfonate group to BDD, and the formed PFCs radicals were decarboxylated or desulfonated to yield the perfluoroalkyl radical which permitted a defluorination reaction between perfluoroalkyl radical and hydroxyl radical. The effects of potential, current density, initial pH, and perfluorooctanoate (PFOA) concentration on the removal of PFOA were investigated. The anodic potential played an important role in the decomposition, and the oxidation potential of PFOA was 2.76 vs. SCE/V (saturated calomel electrode). When the current density increased slightly from 0.12 to 0.59 mA cm−2, PFOA removal was greatly enhanced from 0 to 97.48%. PFOA decomposition was higher in acidic solution compared to that in the alkaline solution. The pseudo-first order kinetic constants of PFOA decomposition increased with the increase of initial concentration.

► The first order kinetic constants of PFCs depend on chain length.
► BDD has good electrochemical performances and high current efficiency at 0.59 mA cm−2.
► The intermediate products of PFCs decomposition were short chain PFCAs.