Abstract: In this study, six boron-doped diamond (Nb/BDD) electrodes with different boron doping levels were prepared using niobium flakes as the substrate by microwave plasma chemical vapor deposition, and the effects of different boron doping levels on the electrochemical performance of the Nb/BDD electrodes and their oxidation of perfluorooctanoic acid (PFOA) were investigated and applied to the electrochemical removal of different PFASs. The results showed that with the increase of boron doping level, the grain size of the Nb/BDD film gradually decreased and the electron transfer rate on the electrode surface gradually increased, but the decrease of film quality leads to the increase of its exfoliation rate.Na2SO4 was used as the electrolyte, and the Nb/BDD electrode as the anode was able to oxidize perfluorooctanoic acid (PFOA) within 120 min at a current density of 30 mA?cm-2. PFOA degradation rate to 78.3% and mineralization rate to 78.1% within 240 min. Among the six Nb/BDD electrodes prepared with different boron doping levels, the medium and low-doped Nb/BDD electrodes have higher degradation and mineralization ability for PFOA, indicating that the efficient electrochemical removal of PFAS can be achieved by regulating the boron doping level of BDD. The analysis of the degradation products indicated that the electrochemical degradation of PFOA followed the law of carbon chain step-by-step removal, in which the direct electron transfer between the anode and the pollutant was the key initiation step of degradation. The electrochemical degradation of perfluorosulfonic acid (PFSA) and perfluorocarboxylic acid (PFCA) with different chain lengths revealed that the length of the carbon chain was inversely proportional to the degradation rate and mineralization rate of PFAS, and thus the short-chain products generated by the degradation were the main reason for limiting the complete mineralization of PFAS. In the future, more attention needs to be paid to the efficient removal of short-chain and ultrashort-chain PFAS in order to meet the demand for the complete detoxification of PFAS through electrochemical technologies.

Key words: Perfluorooctanoic compounds, Boron-doped diamond electrodes, Electrochemical oxidation, New pollution