Rate, Efficiency, and Mechanisms of Electrochemical Perfluorooctanoic Acid Degradation with Boron-Doped Diamond and Plasma Electrodes

Abstract

The removal of per- or polyfluorinated alkyl substances (PFAS) has received increasing attention because of their extreme stability, our increasing awareness of their toxicity at even low levels, and scientific challenges for traditional treatment methods such as separation by activated carbon or destruction by advanced oxidation processes. Here, we performed a direct and systematic comparison of two electrified approaches that have recently shown promise for effective degradation of PFAS: plasma and conventional electrochemical degradation. We tailored a reactor configuration where one of the electrodes could be a plasma or a boron-doped diamond (BDD) electrode and operated both electrodes galvanostatically by continuous direct current. We show that while both methods achieved near-complete degradation of PFAS, the plasma was only effective as the cathode, whereas the BDD was only effective as the anode. Compared to the BDD, plasma required more than an order of magnitude higher voltage but lower current to achieve similar degradation efficiency with more rapid degradation kinetics. All these factors considered, it was noted that plasma or BDD degradation resulted in similar energy efficiencies. The BDD electrode exhibited zero-order kinetics, and thus, PFAS degradation using the conventional electrochemical method was kinetically controlled. On the contrary, analysis using a film model indicated that the plasma degradation kinetics of PFAS using plasma were mass-transfer-controlled because of the fast reaction kinetics. With the help of a simple quantitative model that incorporates mass transport, interfacial reaction, and surface accumulation, we propose that the degradation reaction kinetically follows an Eley–Rideal-type mechanism for the plasma electrode, and an intrinsic rate constant of 2.89 × 108 m4 mol–1 s–1 was obtained accordingly. The investigation shows that to realize the true kinetic potential of plasma degradation for water treatment, mass transfer to the interface must be enhanced.

Investigating the Electrochemically Driven Capture and Release of Long-Chain PFAS by Redox Metallopolymer Sorbents

“…Thus, we conclude that the synthetic tunability of metallopolymers can have an important impact on the energy efficiency, electrosorption, and reversibility toward long-chain PFAS removal. Going forward, we seek to evaluate the integration of our electrochemical separation systems with PFAS destruction and mineralization technologies, with potential methods to consider including plasma degradation or advanced oxidation methods such as boron-doped diamond electrodes …”

“…Going forward, we seek to evaluate the integration of our electrochemical separation systems with PFAS destruction and mineralization technologies, with potential methods to consider including plasma degradation or advanced oxidation methods such as boron-doped diamond electrodes. 73…”

Imparting Selective Fluorophilic Interactions in Redox Copolymers for the Electrochemically Mediated Capture of Short-Chain Perfluoroalkyl Substances

“…Future work will focus on the adaptation of this system for larger-scale applications, including the combination of upconcentration with subsequent degradation of short-chain PFAS. Integration of this system with electrocatalytic degradation methods, such as boron-doped diamond electrodes or plasma processes, can serve as a platform to efficiently degrade short-chain PFAS. ,, …”

Plasma Electrochemistry for Carbon–Carbon Bond Formation via Pinacol Coupling

“…Finally, a reaction-diffusion model is developed to explain the observed kinetics and ab initio calculations are performed to provide insight into the mechanism. Pinacol coupling was carried out by a plasma-liquid process using a direct-current electrolytic configuration that has been detailed in previous reports 40 (Figure S1). We focused our parametric study on MFB as the substrate in a solvent mixture of methanol (MeOH) and water.…”

“…Pinacol coupling was carried out by a plasma-liquid process using a direct-current electrolytic configuration that has been detailed in previous reports (Figure S1). We focused our parametric study on MFB as the substrate in a solvent mixture of methanol (MeOH) and water.…”