(758i) Redox-Active Organometallic Polymers for Small Molecule Separations

Electroactive polymers are a class of stimuli-responsive materials with great potential as energy storage materials, drug release platforms, and electrocatalysts. Organometallic polymers are particularly attractive for selective binding processes due to the ability to molecularly tune their Faradaic processes based on ligand and metal design.¹ Here, we present a series of redox-active metallocene polymers for the selective separation of small molecules for environmental and chemical process applications.

For the anode, investigations with poly(vinyl)ferrocene (PVF) have previously shown significant ion-selective binding properties of these redox-electrodes towards various organic functional groups, especially carboxylates. During oxidation, poly(vinyl)ferrocenium specifically binds to carboxylates with >300-fold separation factors and >250 mg/g adsorption capacities.² We show that through organic modification of the ligand, these anion-metallocene interactions can be enhanced even further to achieve fine chemical separations between very similar, substituted benzoic acids, through modulation of the redox-properties. In parallel, at the cathode, cobalt-based polymers [based on Cobaltocenium (PMAECoCp₂) and (η⁵-cyclopentadienyl)-cobalt(η⁴-tetraphenyl-cyclobutadiene) (PCpCoCb) complexes] are utilized to asymmetrically couple with the anode ferrocene to enhance electrochemical performance.³ In particular, during reduction PCoCpCb can become negatively charged and selectively remove a range of cations, including heavy metals and aromatic organics. Finally, we show recent work on how these tandem asymmetric systems can be used for efficient bulk deionization.

Thus, whether used individually or in tandem, properly designed redox-active polymers have shown to be efficient materials for achieving selective ion-binding in both aqueous and organic media, at moderate to low voltage windows - pointing to their unique capability as a bridge between energy and environmental applications.

References

(1) Su, X.; Hatton, T. A. Advances in Colloid and Interface Science 2016. 10.1016/j.cis.2016.09.001.

(2) Su, X.; Kulik, H. J.; Jamison, T. F.; Hatton, T. A. Advanced Functional Materials 2016, 26, 3394.

(3) Su, X.; Tan, K. J.; Elbert, J.; Ruttiger, C.; Gallei, M.; Jamison, T. F.; Hatton, T. A. Energy & Environmental Science 2017, ASAP article.