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

The remediation of perfluoroalkyl substances (PFAS) is an urgent challenge due to their prevalence and persistence in the environment. Electrosorption is a promising approach for wastewater treatment and water purification, especially through the use of redox polymers to control the binding and release of target contaminants without additional external chemical inputs. However, the design of efficient redox electrosorbents for PFAS faces the significant challenge of balancing a high adsorption capacity while maintaining significant electrochemical regeneration. To overcome this challenge, we investigate redox-active metallopolymers as a versatile synthetic platform to enhance both electrochemical reversibility and electrosorption uptake capacity for PFAS removal. We selected and synthesized a series of metallopolymers bearing ferrocene and cobaltocenium units spanning a range of redox potentials to evaluate their performance for the capture and release of perfluorooctanoic acid (PFOA). Our results demonstrate that PFOA uptake and regeneration efficiency increased with more negative formal potential of the redox polymers, indicating possible structural correlations with the electron density of the metallocenes. Poly(2-(methacryloyloxy)ethyl cobaltoceniumcarboxylate hexafluorophosphate) (PMAECoPF6) showed the highest affinity toward PFOA, with an uptake capacity of more than 90 mg PFOA/g adsorbent at 0.0 V vs Ag/AgCl and a regeneration efficiency of more than 85% at -0.4 V vs Ag/AgCl. Kinetics of PFOA release showed that electrochemical bias greatly enhanced the regeneration efficiency when compared to open-circuit desorption. In addition, electrosorption of PFAS from different wastewater matrices and a range of salt concentrations demonstrated the capability of PFAS remediation in complex water sources, even at ppb levels of contaminants. Our work showcases the synthetic tunability of redox metallopolymers for enhanced electrosorption capacity and regeneration of PFAS.