Electrochemical oxidation of perfluorooctane sulfonate (PFOS) substitute by modified boron doped diamond (BDD) anodes

BDD/SnO2-F electrode was synthesized by spin-coating and heat treatment, and it was characterized by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), and linear sweep voltammetry (LSV). Electrochemical oxidation of chlorinated polyfluorinated ether sulfonate (F-53B, ClCF2CF2CF2CF2CF2CF2-O-CF2CF2-SO3K) as PFOS substitute was carried out with the BDD, BDD/SnO2, BDD/PbO2, and BDD/SnO2-F anodes. The effects of F and Sn ratio, current density, initial pH, initial F-53B concentration, the supporting electrolyte, NaCl concentration, and electrode distance on the degradation ratios were investigated. The defluorination and the desulfurization were evaluated by ion chromatography and UV–vis spectra. The intermediate products were analyzed on the liquid chromatography system coupled with a triple-stage quadrupole mass spectrometer (LC-MS/MS). The experimental results showed that BDD/SnO2-F had the most outstanding electrochemical oxidation performance. After introduction of F into SnO2 crystal, the grain size of SnO2-F was reduced, the oxygen evolution potential was increased by 0.13 V, and the degradation ratio of F-53B was increased by 15.07%. Under the optimum operating parameters, F-53B removal ratio of 95.6% was obtained, and the defluorination ratio reached 61.39% with NaCl supporting electrolyte concentration of 1 mol/L at current density of 30 mA/cm2 after electrolysis of 30 min. Finally, the electrochemical degradation pathways and the mechanisms of F-53B were proposed based on the intermediate products and the previous literature reported. This study indicates that the electrochemical performance of BDD anode can be much improved by modification with SnO2-F, and BDD/SnO2-F anode is kind of effective anode to decompose refractory compounds.