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

Abstract

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) (PMAECoPF 6 ) 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.

Surface-Initiated Living Anionic Polymerization of Functional Methacrylates from the Surface of Organic Particles

“…FMMA in an 89% yield was obtained (Figures S2 and S3), which is 25% higher than the literature value of 64%. The purity of the monomer was also significantly increased compared to the literature, whereby one sublimation was sufficient for anionic polymerization compared to repeated sublimation and purification steps, as published before. , …”

“…1-Methylnaphthalene was distilled twice under reduced pressure. Hydroxymethylferrocene, poly­(methyl methacrylate) (PMMA), and poly­(ferrocenylmethyl methacrylate) (PFMMA) were synthesized as described previously.…”

Molecularly Selective Polymer Interfaces for Electrochemical Separations

“…Redox-active polymers possess sites that can be switched on/off by an applied potential or current, enabling reversible binding or the release of target species. The selectivity of redox polymers can be not only controlled by the electrochemical properties of redox-active centers but also fine-tuned further through the incorporation of non-redox-active pendant groups into the redox-active center ,− and non-redox-active moieties into copolymer design. ,− Consequently, the careful selection of redox-active centers, non-redox-active functional groups, and appropriate polymer design has been a long-standing topic of interest in achieving highly selective and efficient separation processes.…”

Polycobaltoceniumylmethylene – A Water-Soluble Polyelectrolyte Prepared by Ring-Opening Transmetalation Polymerization

“…The electrochemical behavior of 1-Cl was studied by cyclic voltametric measurements (CV) due to the cationic cobaltocenium center exhibiting redox-mediated switching capabilities (Figure ) and potential applications of such materials for switching the surface wettability or selective and redox-mediated interaction with ions or molecules, which will be investigated in the future. ,,,,,− …”

“…In general, metallocene-based polymers can be classified into main-chain and side-chain metallocene-containing polymers, whereby both types have been widely investigated and reported for a variety of applications ranging from biomedical applications to usage in catalysis, electronics, sensing or smart materials, and as precursors for nanostructured ceramics. − In contrast to the well-known ferrocene-based polymers, the corresponding isoelectronic, yet positively charged cobaltocenium-based polymers are underinvestigated . Nevertheless, cobaltocenium-based polymers have already demonstrated potential in different areas, like self-assembly, antimicrobial applications, and energy storage, as well as in mechanochemistry and bioconjugation, due to the valuable properties of the air stable cobaltocenium moiety featuring counterion-dependent solubility, high chemical stability, and robustness against oxidizing agents, as well as its antimicrobial properties. ,− The incorporation of cobaltocenium into the main-chain of a polymer gives rise to a cationic polyelectrolyte. However, the inertness of cobaltocenium salts and the convenient oxidation of the corresponding neutral 19-electron cobaltocene complicate the synthesis of cobaltocenium-based polyelectrolytes. , …”