Efficiently degradation of perfluorooctanoic acid in synergic electrochemical process combining cathodic electro-Fenton and anodic oxidation

A synergic electrochemical process between cathodic electro-Fenton and anodic oxidation was proposed for efficient degradation of perfluorooctanoic acid (PFOA) in this work. The electron-transfer ability and hydroxyl radicals ( OH) concentration are the key parameters for the PFOA degradation efficiency. Boron-doped diamond (BDD) anode exhibited the highest anodic oxidation ability compared to platinum and carbon stick. The integrated FeMn-doped carbon aerogel was fabricated as cathode for in-situ enhancing the generation of OH. The X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) indicated the main composition of cathode is Fe0 and MnO. The Fe in the integrated cathode favors the electro-catalytic ability of oxygen reduction reaction (ORR), while MnO enhances the selectivity of 2-electron ORR with H2O2 as main product. The electroformed H2O2 would be onsite catalytic decomposition with FeII and MnII as Fenton catalysts for in-situ generating OH radicals. The optimal cathode with Fe/10Mn weight ratio can generate the highest concentration of OH. The catalytic degradation efficiency in this synergic electro-catalysis process with BDD as anode and Fe10MnC as cathode reached nearly 97% PFOA removal and 93% TOC removal after 4 h, suggesting the prominent synergic combination of cathodic electro-Fenton and anodic oxidation. The amount of intermediates C6F13COO− was decreased while others including C5F11COO−, C4F9COO−, C3F7COO−, C2F5COO−, CF3COO− were increased with increasing electro-catalysis time. The NEXAFS analysis of F in solution and cathode surface further confirmed the continuously synergic electro-catalysis between anodic and cathodic electro-Fenton oxidation.