(226g) Greener Teams: Tethered Electrolyte Active-Layer Membranes Produced By Surface-Initiated Free Radical Polymerization

As the world shifts toward sustainable energy sources, the recovery of valuable elements such as lithium and uranium has gained increasing importance. Nanofiltration (NF) membranes are garnering attention as promising candidates for addressing complex separations involving species with similar chemical properties, sizes, and charges. A notable advancement in this realm is the development of tethered electrolyte active-layer membranes (TEAMs). These TEAMs were developed by employing surface-initiated atom transfer radical polymerization (SI-ATRP) to grow neutral monomer precursors from an ultrafiltration cellulose substrate, subsequently modifying them into ionizable groups. However, SI-ATRP necessitates the use of harsh organic solvents, metal catalysts, and a multistep synthesis process, rendering it ecologically unfriendly and unsuitable for large-scale industrial applications. In this study, we propose an environmentally sustainable and scalable alternative by utilizing surface-initiated free radical polymerization (SI-FRP) for the development of greener TEAMs. Monomers, methacroylcholine chloride (MACC), acrylic acid (AA), and sodium 4-vinylbenzenesulfonate (SVBS) were grafted on the surface of commercial ultrafiltration cellulose membranes as positive and negative TEAMs, respectively. The positive TEAMs showed rejection of 97% of CaCl₂ and 83% of NaCl using feeds of 2 mM salt concentration with a permeability of around 4.3 L m^-2 h^-1 bar^-1. Meanwhile, 95% Na₂SO₄ and 78% of NaCl rejection with a permeability of 8.2 L m^-2 h^-1 bar^-1 was attained with the negative TEAMs. In addition, monovalent selectivity was probed for varied proportions of monovalent versus divalent co-ions. TEAMs exhibited the greatest monovalent selectivity with a feed of 75% divalent co-ions, with a cation selectivity of about 8 and an anion selectivity of about 9. This study shows that scalable methods may be used to produce ion-ion selective membranes toward resource recovery.