Monovalent Ion Transport in Sulfonated Poly(arylene ether sulfone) Membranes

Currently, 1.42 billion people - nearly one-fifth of the world’s population - live in regions experiencing high water vulnerability. As the climate emergency and population growth increase the strain on freshwater systems, it is clear that alternative methods of obtaining clean water, such as seawater desalination, are needed to supplement existing sources. Thermal methods for filtering water, e.g., multi-effect distillation, are highly energy intensive and, because of this, cannot realistically meet modern needs. As such, current water purification systems rely on polymer membranes, which enable lower cost, higher efficiency, and lower energy filtration. This said, effective, mechanically and chemically robust, and eco-friendly polymer membranes are needed.

Modern membrane filtration technologies predominantly use polyamide-based thin film composite membranes, which boast impressive separation capabilities, but are susceptible to degradation, most notably via chlorine attack. As such, researchers have looked for alternative chemically stable polymers, e.g. polysulfones. These polymers exhibit several appealing traits: high mechanical and thermal stability, solubility in common organic solvents, and resistance to oxidative attack. Unfortunately, non-functionalized polysulfone membranes are quite hydrophobic leading to low water flux, which hinders performance in water filtration applications. To combat this issue, polysulfones can be sulfonated to increase the hydrophilicity and, in turn, the water flux, which is coupled to the productivity of the membrane in a desalination application.

This presentation reports experimental characterization of a series of sulfonated poly(arylene ether sulfones). The ion separation properties of these materials are of increasing interest due to a shift in focus from simply salt rejection, which has been used for decades to characterize desalination membranes, to the use of membranes for ion fractionation (or ion specific separations). Focusing primarily on transport properties, we discuss the impact of polymer sulfonation and counter-ion form on competitive monovalent ion transport. Specifically, we report sodium (Na⁺) and lithium (Li⁺) transport data for a series of sulfonated poly(arylene ether sulfone) (BPS) polymers to inform the use of such materials in emerging ion separation applications that could be important for critical materials extraction, recovery, and recycling.