Elucidating Molecular Design Principles for Copolymer Membranes with Solute-Tailored Selectivity for the Separations of Rare Earth Elements

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Rare-earth elements (REEs) are essential components in modern electronic devices and green energy technologies. For example, high flux magnets that contain REEs are critical to the operation of hard drives, wind turbines, and electric motors. Identifying methods to separate REEs from domestic ore deposits or recycle them from outdated electronics is critical to maintaining a reliable supply of these materials. The solvent extraction processes currently used to isolate these resources consume large amounts of chemical reagents and energy while producing large volumes of wastewaters. As such, traditional REE separation processes are difficult to implement sustainably. Membrane separations have demonstrated significant advantages in sustainability and energy efficiency in numerous other applications. To translate this paradigm to REE separations, membranes capable of distinguishing between REE ions are needed. However, REE ions have comparable sizes and the same charge when dissolved in solution, which makes them challenging to separate. This multidisciplinary project integrates recent advances in the fields of membrane science, polymer chemistry, and data science to address fundamental scientific questions related to the interfacial and thermodynamic phenomena that allow for the selective transport of REEs across polymer membranes. Systematic, experimental studies will be conducted to describe how membrane nanostructure, surface chemistry, and REE transport mechanisms are related. The fundamental knowledge to be gained has broad implications for the molecular engineering of selective membranes that address other critical separation challenges needed to ensure the well-being and prosperity of the American people. For example, by changing the membrane nanostructure and chemistry, molecular transport mechanisms can be tailored to enable the purification of therapeutic medicines or the treatment of drinking water. This project also helps revolutionize the separation science landscape of the U.S. by training the next cohort of interdisciplinary scientists and engineers.The overall goal of this proposal is to engineer novel membrane systems capable of separating REEs sustainably. Currently, there is no clear understanding of the interfacial and thermodynamic phenomena underlying the transport mechanisms that are capable of fractionating REE ions. Addressing this critical knowledge gap necessitates identifying the nanostructural and chemical control factors that govern the ability of membranes to permeate target solutes based on chemical identity. As such, the following specific aims will be pursued to establish quantitative structure-property relationships for the phenomena underlying solute-tailored transport mechanisms. (1) Fabricate and characterize copolymer membranes that are amenable to post-synthetic functionalization. This versatile materials platform offers orthogonal control over membrane nanostructure and chemistry such that a diverse array of interfacial and thermodynamic phenomena can be interrogated. (2) Develop a statistical learning framework to navigate the vast molecular design space associated with copolymer materials efficiently. Model-based design of experiments (MBDOE) and dynamic diafiltration experiments are proposed to identify the dominant interfacial phenomena up to 100 times faster than Edisonian searches. (3) Utilize statistical learning to guide the development of structure-property relationships for selective transport mechanisms in copolymer membranes. This research program presents an opportunity to make significant progress toward elucidating the critical relationships for membranes capable of transporting target solutes based on chemical, rather than steric, factors, having applications well beyond REE separations. Moreover, the proposed work offers a new, high-throughput paradigm to characterize membranes using dynamic experiments and MBDOE.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.