Redox-copolymers for the recovery of rare earth elements by electrochemically regenerated ion-exchange

Abstract

Rare earth elements (REEs) play an essential role in our modern society, being critical resources for electronic devices and renewable energy technologies. Efficient platforms for REE recovery and purification are essential to resource security and environmental management. Imparting electrochemical control over an adsorbent system can lead to higher modularity and sustainability, by enabling adsorbent regeneration without the use of additional chemicals. For the reversible capture and release of REEs, we design and synthesize a redox-copolymer, poly(ferrocenylpropyl methacrylamide-co-methacrylic acid) (P(FPMAm-co-MAA)), that combines an ion-exchange carboxyl group for REE adsorption, and a redox-active ferrocene moiety for regeneration based on electrochemical control. By molecularly tuning the copolymer composition, efficient adsorption uptake could be achieved alongside electrochemically regenerated adsorbent reuse. The copolymer electrodes exhibited an Y(III) adsorption capacity of 69.4 mg Y per g polymer, and electrochemically mediated regeneration efficiency close to 100% through oxidation of the ferrocenium units. The copolymer sorbent showed stoichiometric binding for cerium (Ce), neodymium (Nd), europium (Eu), gadolinium (Gd), and dysprosium (Dy) based on carboxyl active sites. Our work provides a proof of concept for electrochemically regenerable ion-exchange copolymers for REE recovery, and we envision generalized applications of this concept in electrifying ion-exchange systems and cation-selective separations.