(404d) Reactive Block Polymer Membranes Tailored for Heavy Metal Ion Separations

The development of novel polymeric materials that enable the fabrication of nextgeneration membranes capable of separating target solutes from solution has been a major focus of recent membrane research. While steric exclusion (i.e., size-selectivity) is the most basic mechanism for membrane separations, new polymeric materials are being developed for chemically-selective membrane adsorbers that allow for efficient, high throughput separations. These adsorptive membranes can be utilized for the removal of pollutants such as heavy metal ions, the concentration of chemical products, or the chromatographic separations of valuable biopharmaceuticals. The novel block polymer materials discussed in this talk are an exciting materials platform for the fabrication of membrane adsorbers because they provide the ability to rationally engineer adsorption capacity through the controlled synthesis of the macromolecular precursor. In this work, the triblock polymer poly(isoprene-b-styrene-b-N,N-dimethyacrylamide) (PI-PS-PDMA) is cast into asymmetric membranes using a technique that can be implemented in roll-to-roll fabrication processes for large scale applications (i.e., the self-assembly and nonsolvent induced phase separation (SNIPS) method). The self-assembled polymer results in a high density of consistently-sized nanoscale pores, which are lined with by poly(N,Ndimethylacrylamide) (PDMA) moieties. The PDMA groups that lines the pore walls are converted by simple hydrolysis to polyacrylic acid (PAA) groups, which can be easily reacted to other functionalities that are molecularly-designed for target applications. For example, upon reaction with cysteamine at room temperature, the pore-lining groups are converted to N-(2- ethanethiol) polyacrylamide (PASH) moieties that act as high capacity binding sites for heavy metal ions, including lead, gold, cadmium, and silver cations. When placed in a solution containing lead (II) ions, this PASH-functionalized membrane is able to adsorb up to 470 mg Pb²⁺ per gram of membrane, which compares favorably with other state-of-the-art lead adsorbers in the field (500 mg g^-1). Alternatively, a distinct membrane functionalization protocol can be executed to affix glutathione, an antioxidant that acts as a ligand for heavy metal ions in the cells of many organisms, to the pore walls. The glutathione-laden membrane is capable of heavy metal adsorption at high capacity even in very low concentration solutions like those that may occur in water treatment systems and natural environments. At concentrations as low as 10 ppm Pb²⁺, the glutathione-functionalized membrane was able to remove over 95% of the heavy metal content from solution. Furthermore, the adsorption capacity of the membrane could be regenerated upon addition of a mildly acidic solution. Membranes that are based on these novel polymeric materials and are capable of this quality of separation performance provide a scalable and efficient adsorption platform that can be tailored to myriad chemically-selective separations in future applications.