(4ja) Redox-Mediated Electrochemical Separations for Desalination, Environmental Remediation, and Resource Recovery

Process-intensified separations using sustainable technologies have become crucial for addressing both environmental and energy crises. Electrochemical separations have gained increasing attention due to their sustainable and modular platforms, which are applied in areas such as desalination, environmental remediation, and the recovery of valuable species.¹ The transition from non-selective materials to advanced electrodes, membranes, and system designs has enabled the selective separation of minor species and the discrimination of desired species from multicomponent mixtures. During my Ph.D. program at UIUC, under the supervision of Professor Xiao Su, my research focused on advancing electrochemical separations by integrating polymer design with system engineering to improve selectivity and process-intensification. My research aims can be categorized into three main advancements: i) introducing new intermolecular interactions into redox-polymers, ii) modifying membranes for multicomponent separations, and iii) engineering system designs for process-intensified and continuous separation systems.

By incorporating an additional non-covalent interaction, such as halogen bonding (XB), into a redox polymer, I expand the potential for selective electrochemical separation to non-aqueous media.² This study opens new opportunities for the electrochemically-driven recovery of valuable organic species from chemical manufacturing processes. Upon oxidation of the cooperative, synergistic redox center, the amplified halogen bonding site facilitates selective electrosorption and release of target inorganic (e.g., chloride) and organic species (e.g., benzene sulfonate) at a heterogeneous interface.

Advancing membranes with a layer-by-layer (LBL) functionalization strategy has enabled precise control of membrane selectivity for the electrochemical recovery of organic acids from multicomponent fermentation broths.³ By tailoring the physicochemical properties of ion-exchange membranes through a layer-by-layer (LBL) approach, we achieved complete retention of succinate while enhancing the overall flux for inorganic ions. Integrating the functionalized membrane into the redox-mediated electrodialysis (ED) system facilitates continuous up-concentration of succinate alongside the partitioning of unreacted sugar and inorganic ions, paving the way for modular multicomponent separations in biomanufacturing processes.

By substituting energy-intensive water-splitting reactions with reversible redox reactions, I developed a redox-mediated electrodialysis platform for energy-efficient and continuous separation processes.^4-6 Utilizing a single water-soluble redox species for both cathodic and anodic reactions, the system significantly reduced energy consumption in facilitating ion migration for various separation processes from desalination⁴ to metal⁶ and biomolecule separations.^{3, 5} Particularly, combining water-soluble redox copolymers with nanofiltration membranes (NF) effectively addressed longstanding limitations of electrochemical systems with ion-exchange membranes, such as high-cost and membrane fouling. This NF-enabled redox-polymer ED system enabled treating a wide range of charged species, from inorganic salts to organic contaminants, to produce potable water without membrane fouling.⁴

Teaching Interests

As a mentor and educator, I prioritized fostering self-motivation in my mentees and students. I believe that guiding students to build ownership of their problem-solving path is crucial for their long-term success and personal growth. Throughout my M.S. and Ph.D. programs, I actively engaged as a research mentor, teaching assistant, and mentoring volunteer to develop a range of teaching strategies. I aimed to enhance students’ self-directed learning by nurturing critical thinking, problem-solving, decision-making, and communication skills. Ultimately, my goal as an educator is to build an enjoyment of learning and confidence to pursue their dreams passionately, thus ultimately devoting themselves to making a positive impact in the world.

Building upon my interactions with students, I am excited to integrate my pedagogical approaches with core chemical engineering courses such as transport phenomena, chemical design, thermodynamics, and electrochemistry. These core chemical engineering classes require a high level of problem-solving skills, critical thinking, and dedicated effort. In addition to imparting technical knowledge, I aim to empower students to develop resilience to overcome challenges, encourage active engagement, and inspire them to pursue their larger purpose within the community and the world.

References

(1) Kim, N.; Oh, W.; Knust, K. N.; Zazyki Galetto, F. b.; Su, X. Molecularly Selective Polymer Interfaces for Electrochemical Separations. Langmuir 2023, 39 (47), 16685-16700.

(2) Kim, N.; Jeyaraj, V. S.; Elbert, J.; Seo, S. J.; Mironenko, A. V.; Su, X. Redox-Responsive Halogen Bonding as a Highly Selective Interaction for Electrochemical Separations. Journal of the American Chemical Society Au.

(3) Kim, N.; Lee, J.; Su, X. Precision Tuning of Highly Selective Polyelectrolyte Membranes for Redox-Mediated Electrochemical Separation of Organic Acids. Advanced Functional Materials 2023, 33 (12), 2211645.

(4) Kim, N.; Elbert, J.; Kim, C.; Su, X. Redox-Copolymers for Nanofiltration-Enabled Electrodialysis. ACS Energy Letters 2023, 8 (5), 2097-2105.

(5) Kim, N.; Jeon, J.; Elbert, J.; Kim, C.; Su, X. Redox-mediated electrochemical desalination for waste valorization in dairy production. Chemical Engineering Journal 2022, 428, 131082.

(6) Kim, N.; Su, X.; Kim, C. Electrochemical lithium recovery system through the simultaneous lithium enrichment via sustainable redox reaction. Chemical Engineering Journal 2021, 420, 127715.