Electrochemical Advanced Oxidation of Perfluorooctanoic Acid: Mechanisms and Process Optimization with Kinetic Modeling

Abstract

Electrochemical advanced oxidation processes (EAOPs) are promising technologies for perfluorooctanoic acid (PFOA) degradation, but the mechanisms and preferred pathways for PFOA mineralization remain unknown. Herein, we proposed a plausible primary pathway for electrochemical PFOA mineralization using density functional theory (DFT) simulations and experiments. We neglected the unique effects of the anode surface and treated anodes as electron sinks only to acquire a general pathway. This was the essential first step toward fully revealing the primary pathway applicable to all anodes. Systematically exploring the roles of valence band holes (h + ), hydroxyl radicals (HO • ), and H 2 O, we found that h + , whose contribution was previously underestimated, dominated PFOA mineralization. Notably, the primary pathway did not generate short-chain perfluoroalkyl carboxylic acids (PFCAs), which were previously thought to be the main degradation intermediates, but generated other polyfluorinated alkyl substances (PFASs) that were rapidly degraded upon formation. Also, we developed a simplified kinetic model, which considered all of the main processes (mass transfer with electromigration included, surface adsorption/desorption, and oxidation on the anode surface), to simulate PFOA degradation in EAOPs. Our model can predict PFOA concentration profiles under various current densities, initial PFOA concentrations, and flow velocities.

Inorganic Electrified Membrane: From Basic Science to Performance Translation

“…The specific structures of different PFAS and Ti 4 O 7 crystals, transition states of PFAS transformation, and the degradation pathways can be calculated by DFT. , For instance, DFT is applied to evaluate the thermodynamic preference of possible elementary steps of the overall PFAS degradation. The calculated adsorption energy of PFAS and transition states of these elementary steps coordinate well with the experimental results, which can guide the rational design of the Ti 4 O 7 IEM structure and components. , In addition, the operation conditions of the Ti 4 O 7 IEM including current density and flux can be adjusted to improve the PFAS degradation performance. , Relevant mathematic models revealed that the mass transfer rate and electric energy consumption escalate along with the flux across the Ti 4 O 7 IEM.…”

“…The calculated adsorption energy of PFAS and transition states of these elementary steps coordinate well with the experimental results, which can guide the rational design of the Ti 4 O 7 IEM structure and components. 55,56 In addition, the operation conditions of the Ti 4 O 7 IEM including current density and flux can be adjusted to improve the PFAS degradation performance. 53,57 Relevant mathematic models revealed that the mass transfer rate and electric energy consumption escalate along with the flux across the Ti 4 O 7 IEM.…”

Electrosorption, Desorption, and Oxidation of Perfluoroalkyl Carboxylic Acids (PFCAs) via MXene-Based Electrocatalytic Membranes

“…To examine the effect of surface termination of MXenes on PFCA degradation, we calculated the free energies of different possible intermediates according to a reported degradation pathway for PFOA over three models (Ti 3 C 2 Cl 2 , Ti 3 C 2 F 2 , and Ti 3 C 2 O 2 ) . The overall pathways are shown in Figure b.…”

“…Figure 1a To examine the effect of surface termination of MXenes on PFCA degradation, we calculated the free energies of different possible intermediates according to a reported degradation pathway for PFOA over three models (Ti 3 C 2 Cl 2 , Ti 3 C 2 F 2 , and Ti 3 C 2 O 2 ). 49 The overall pathways are shown in Figure 1b. First, in this degradation pathway, deprotonated PFOA (C 7 F 15 COO − ) exhibited the strongest adsorption energy on • radical and COF 2 ; COF 2 could rapidly react with water to finally form CO 2 and HF.…”

Degradation of Perfluorooctanoic Acid by Chlorine Radical Triggered Electrochemical Oxidation System

“…Several technologies have been developed to degrade PFASs, including high-temperature pyrolysis, electrochemical oxidation (EO), UV photooxidation, UV photoreduction, and ultrasonic irradiation . Among these technologies, EO technology has been proven to be an efficient method to degrade PFASs. , A great deal of research has focused on developing EO anode materials with excellent performance, such as boron/nitrogen B/N codoped diamond, Ti/SnO 2 –Sb-Bi, Ti/SnO 2 –Sb/PbO 2 , and Magnéli phase Ti 4 O 7 , , for degrading PFASs. Nevertheless, the roles of the various oxidative free radicals generated by electrochemical systems lack detailed evaluation.…”