Efficient Mineralization of Perfluorooctanoate by Electro-Fenton with H2O2 Electro-generated on Hierarchically Porous Carbon

Abstract

Perfluorochemicals are environmentally persistent, bioaccumulative, and globally distributed contaminants, which present potential toxicity to both humans and ecosystems. However, rapid mineralization of perfluorochemicals with cost-effective method remains great challenges. Here, an electro-Fenton system was reported for efficient mineralization of perfluorooctanoate (PFOA), where H2O2 was electro-generated in situ from O2 reduction on hierarchically porous carbon (HPC). Benefited from the high H2O2 production rate (41.2-14.0 mM/h) of HPC, PFOA (50 mg/L) was rapidly degraded by electro-Fenton with first-order kinetic constants of 1.15-0.69 h(-1) at low potential (-0.4 V) in a wide range of pH (2-6). Meanwhile, PFOA was effectively mineralized, as revealed by a total organic carbon removal efficiency of 90.7-70.4% (-0.4 V, pH 2-6, 4 h). Moreover, the current efficiency of this electro-Fenton system for PFOA degradation was 1 order of magnitude higher than those of electrochemical oxidation. On the basis of the intermediate analysis, we proposed a possible mechanism for PFOA degradation: PFOA lost one electron to the anode and got decarboxylated. The formed perfluoroalkyl radical was mainly oxidized by hydroxyl radical, resulting in the formation of shorter chain perfluorocarboxylic acid, which followed the same reaction cycle as PFOA until it was mineralized.