Treatment of non-traditional source waters, such as agricultural runoff and produced water, offers exciting opportunities for membrane technologies to facilitate resource recovery and fit-for-purpose water production. In particular, next generation membranes exhibiting solute-tailored selectivity could facilitate recovery of valuable solutes such as lithium from brines and wastewater that is not possible using conventional materials. Addressing these challenges requires developing functional polymers capable of achieving precision separations, such as monovalent or divalent ion selectivity. Unfortunately, identifying functional ligands capable of facilitating solute-specific membrane separation is hindered by the difficulty of incorporating diverse chemical moieties into membrane materials, which typically requires tedious redesign of monomer and polymer chemistries. These limitations have further impeded development of structure-property relationships connecting membrane chemistry to water and ion transport and separation properties. We addressed these challenges by developing a versatile synthetic platform capable of generating a library of functional membranes using active ester chemistry. Poly(ethylene glycol) diacrylate (PEGDA) hydrogel membranes were prepared with pentafluorophenyl acrylate comonomers that can easily be substituted after polymerization using a variety of amine-containing ligands. This platform enables control over functional group grafting density, crosslinking density, and membrane water content by facile tuning of monomer ratios. Salt uptake and permeation measurements on a series of membranes with different imidazole ligand densities revealed that ion-imidazole interactions enhance NaCl and LiCl uptake but lack sufficient strength to affect monovalent ion diffusion. Stronger interactions between imidazole ligands and Mg2+ and Cu2+ cations substantially increase MgCl2 and CuCl2 uptake by 2x and 4x, respectively, while slowing salt permeation and diffusion. Pulsed-Field Gradient NMR measurements on membranes with different Lewis base ligands revealed water, lithium, and anion self-diffusion is largely driven by membrane water content, with ligand functionality playing a secondary role. Anion identity was also found to affect water and ion self-diffusion and salt uptake. These mechanistic insights help lay the groundwork for designing advanced membranes for targeted solute separation and resource recovery.

Probing water and ion transport in hydrogel membranes with versatile ligand functionality enabled by active ester substitution

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.