Understanding molecular interactions and design of selective electrochemical processes for water treatment

Water scarcity, resource depletion, and exposure to anthropogenic contaminants have been major drivers for the development of efficient technologies for water remediation. Recently electrochemical separations have emerged as a promising solution due to their modularity, scalability, and potential for net-zero emissions when powered by renewable energy. However, their broader adaptation is limited by poor ion selectivity, which increases energy demands. This challenge is largely dependent on the electrode materials used in electrochemical systems. Developing tailored materials with molecular-level selectivity can help achieve energy-efficient separations. For my doctoral thesis, I investigated the molecular-level interactions and interface morphology governing electrochemical separations of per- and polyfluoroalkyl substances (PFAS), phosphates, and rare earth elements (REE) from water, aiming to enhance selectivity and efficiency in pollutant removal and resource recovery. By designing and characterizing redox-active polymers and ligands, we identified key interactions─ electrostatic, redox, fluorophilic and non-covalent interactions—that drive selective binding and release of target species. For PFAS, we demonstrate that electrostatic interactions predominantly govern capture, while fluorophilic groups selectively enhance uptake of short-chain PFAS. Polymer structure and porosity, influenced by fluorinated monomer content, were shown to further modulate PFAS selectivity via steric effects. Furthermore, integration of electrosorption with electrodegradation enabled energy-efficient PFAS destruction by concentrating contaminants in wastewater prior to oxidation. To recover phosphorus, we developed ferrocene-based polymers which achieved high selectivity over competing ions such as chloride. In-situ neutron reflectometry revealed solvation-driven ion selectivity under dynamic redox modulation, providing insights into polymer design and separation treatment trains. For REE extraction, we demonstrated how the design of ligands can be accelerated via integration with artificial intelligence and chemical language models to yield selective chemistries that lower separation costs. Across all systems, the interplay of interfacial morphology, hydration, and chemical functionality was shown to be critical for efficient separations. The findings of this dissertation provide a framework for designing advanced interfaces for selective separations, with broader implications for sustainable water treatment and applications in industries requiring precise molecular selectivity.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Roman Santiago, Anaira

Contributors dc:contributor

• Su, Xiao
• Cusick, Roland D
• Yang, Hong
• Kong, Hyun J.

• Electrochemistry
• Water Treatment
• Pfas
• Rare Earth Elements

Statement dc:rights

• Copyright 2025 Anaira Roman Santiago

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/130146

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F130146