Development of macroporous Magnéli phase Ti4O7 ceramic materials: As an efficient anode for mineralization of poly- and perfluoroalkyl substances

Abstract

Magnéli phase Ti4O7 ceramic materials having extensive interconnecting macropores with an average pore size of 2.6 μm and 21.6% porosity were fabricated using a high-temperature sintering method, and then tested as an anode in a batch mode for electrooxidative mineralization of environmentally persistent poly- and perfluoroalkyl substances (PFASs) such as perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS). Tests were also conducted with other “non-active” electrodes for comparison, including Ce-doped PbO2 and Ti/BDD electrodes. The results showed that the porous Ti4O7 ceramic anode exhibited greater PFOA/PFOS oxidation rates than those of the other electrodes. Only trace amounts of perfluorocarboxylic acid (PFCAs) with shortened chain lengths were observed as intermediates during PFOA mineralization. SO42− and F− were recovered as the mineralization products of PFOS electrooxidation, while no organofluorine compounds such as shorter-chain PFCAs were detected in the solution by high-resolution mass spectrometry (HRMS). Possible mechanisms for PFOA/PFOS mineralization over porous Ti4O7 ceramic electrode were proposed on the basis of reaction products analysis. In addition, the developed porous Ti4O7 ceramic anode was successfully applied to treatment of the still bottom liquid waste containing high concentrations of poly- and perfluoroalkyl substances (PFASs) as well as high chloride and organic content concentrations from the regeneration of ion-exchange resin that had been used for remediation of PFASs-impacted groundwater. The results illustrate the promise of the macroporous Magnéli phase Ti4O7 ceramic materials for electrochemical treatment of PFASs in water.