Electrochemical degradation of perfluorooctanoic acid in aqueous solution by boron-doped diamond electrodes under pulsed voltage conditions

Abstract

• Degradation of persistent substance by pulsed electrochemical oxidation. • Pulsed degradation more efficient than direct current. • Pulse width affects the degradation rate. • Degradation of PFOA with Pt and graphite electrodes. The aim of this study was the electrochemical degradation with boron-doped diamond (BDD) electrodes using pulsed direct current (PDC). An electrochemical characterization of the BDD electrode in aqueous solution was performed to determine the optimal parameters for the PDC. By means of cyclic voltammetry a capacity of 81 µFcm −2 of the electrolytic double layer was determined and confirmed by impedance spectroscopy. Impedance spectroscopy showed an optimal frequency range of 1–5 Hz and thus an ON-time of the voltage pulse of 100-300 ms. An OFF-time of minimum 100 ms was determined by chronoamperometry. Perfluorooctanoic acid (PFOA) was selected as a model substance to investigate the influence of pulsed operation on electrochemical degradation. Based on the PDC experiments, an amplitude of 8 V was obtained for the pulsed electrochemical degradation of PFOA in aqueous solution. The variation of the ON-time showed an influence on the degradation rate of PFOA. The pulsed degradation with an ON-time and an OFF-time of 300 ms showed a degradation of PFOA of 56%. In contrast, only 42% degradation was achieved under direct current conditions. In addition, comparative experiments were carried out with platinum and graphite electrodes, showing the degradation of PFOA. Degradation and transformation products of PFOA were identified by liquid chromatography with high resolution mass spectrometry.