Electrochemical oxidation of 1H,1H,2H,2H-perfluorooctane sulfonic acid（6：2 FTS） on DSA electrode：Operating parameters and mechanism

The 6：2 FTS was the substitute for perfluorooctane sulfonate（PFOS） in the chrome plating industry in Japan. Electrochemical oxidation of 6：2 FTS was investigated in this study. The degradabilities of PFOS and 6：2 FTS were tested on the Ti/SnO2–Sb2O5–Bi2O3anode. The effects of current density,potential,and supporting electrolyte on the degradation of 6：2 FTS were evaluated. Experimental results showed that 6：2 FTS was more easily degraded than PFOS on the Ti/SnO2–Sb2O5–Bi2O3anode. At a low current density of 1.42 mA/cm2,6：2 FTS was not degraded on Ti/SnO2–Sb2O5–Bi2O3,while the degradation ratio increased when the current density ranged from 4.25 to 6.80 mA/cm2. The degradation of 6：2 FTS at current density of 6.80 mA/cm2 followed pseudo first-order kinetics with the rate constant of 0.074 hr-1. The anodic potential played an important role in the degradation of 6：2 FTS,and the pseudo first-order rate constants increased with the potential. The surface of Ti/SnO2–Sb2O5–Bi2O3was contaminated after electrolysis at constant potential of 3 V,while the fouling phenomenon was not observed at 5 V. The fouled anode could be regenerated by incinerating at 600°C. The intermediates detected by ultra-performance liquid chromatography coupled with a triple-stage quadrupole mass spectrometer（UPLC–MS/MS） were shorter chain perfluorocarboxylic acids. The 6：2 FTS was first attacked by hydroxyl radical,and then formed perfluorinated carboxylates,which decarboxylated and removed CF2 units to yield shorter-chain perfluorocarboxylic acids.