Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical and Environmental Engineering (ENAS)

First Advisor

Elimelech, Menachem

Abstract

Membranes that can separate ionic species of similar size and valency are needed to advance resource recovery for battery and electronic waste recycling, lithium harvesting, and water reuse. Insights from ion channels in biological cell membranes indicate that simultaneous confinement and preferential interactions with binding sites are critical for fast and selective ion transport. However, these specific, localized chemical interactions have yet to be translated to synthetic membrane design. This dissertation attempts to bridge the gap between molecular-level selectivity mechanisms of biological ion channels and the design of ion-selective membranes through systematic investigations of ion transport in precision-model systems. The first system is a virtual nanopore in multi-layer graphene simulated with equilibrium molecular dynamics (MD). We explored how pore features such as diameter, length, and the arrangement of preferential binding sites influence ion transport. A model based on transition state theory was used to estimate ion flux from MD results for >260 simulations and >800 pore architectures. Trade-offs were identified between ion binding site interactions and flux, with optimal site arrangements dependent upon the geometry of each pore. A machine learning model was trained on the MD results to predict ion transport from specified pore features and guide membrane design. To explore ion-pore interactions in real nanoporous materials, UiO-66, a water-stable metal-organic framework (MOF), was used as a model system because it provides nanoscale confinement and tunable pore chemistry. We extended methods to post-synthetically functionalize UiO-66 nanopores with ion-binding chemical groups and measured the impact of pore chemistry on ion sorption kinetics. A technique was developed for in situ MOF deposition in a quartz crystal microbalance to precisely monitor real-time sorption of Co2+, Ni2+, and Cu2+ in functionalized MOFs with nanogram accuracy. By tuning pore chemistry, we attained Cu2+/Co2+ selectivity of 14, despite their similar size and charge. In summary, structure-property relationships were developed for selective ion transport in nanoporous materials through mechanistic studies of an experimental and computational platform. This dissertation demonstrates new approaches to studying nanoconfined transport and illustrates the importance of high-resolution material design for high resolution separations.

Download

Share

COinS