Redox-mediated ion separation and exchange by tailored design of immobilized metallopolymers

Mining and harvesting of valuable components from water or organic phases are urgent challenges. Metallopolymers can show excellent control of the binding and release of target molecules or ions without additional external chemical inputs. Here, we report the covalent functionalization of porous polystyrene microparticles with poly(hydroxyethyl methacrylate) (PHEMA) and poly(ferrocenylmethyl methacrylate) (PFMMA) copolymers and block copolymers via surface-initiated living anionic polymerization to tailor the functionality and polarity of the surface. The metallopolymer-decorated particles were characterized by infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, and the redox-responsiveness was analyzed in different media using cyclic voltammetry. The variation in polarity enabled the investigation of the influence of polarity on the electrochemical performance. The metallopolymer particles were used as efficient ion-adsorbers and ion-exchange materials in both static and flow measurements, and the resulting findings were compared to homopolymer functionalized particles. The adsorption of fluoride, nitrate, and sulfate and their adsorption selectivity were investigated. The capacity of sulfate was increased for hydrophilic particles and remained more constant over time. The results demonstrate the importance of the controlled design of surfaces for tailoring the selectivity of ion-adsorption materials. The insights on the structure-property relation of the metallopolymer design and immobilization pave the way for new adsorption technologies and future design of electrochemically switchable surfaces.