Yang, Yuanxi; (2025) Cucurbit[n]uril-Enhanced Polymeric Membrane for CO₂ Separation Processes. Doctoral thesis (Ph.D), UCL (University College London).

Text Yuanxi Yang_ PhD Thesis.pdf - Submitted Version Access restricted to UCL open access staff until 1 July 2026. Download (9MB)

Abstract

Membrane technology represents a highly promising strategy for CO₂ separation, owing to its low energy demand, cost-efficiency, and system adaptability. Nonetheless, polymeric membranes are fundamentally constrained by the well-established trade-off between permeability and selectivity, which hampers their performance in practical separation processes. This thesis investigates the incorporation of Cucurbit[n]uril (CB[n])—a macrocyclic host molecule comprising n glycoluril units and widely recognised in supramolecular chemistry for its strong and selective host–guest interactions—into polymeric membrane matrices, with the aim of enhancing CO₂ separation performance and mitigating the intrinsic limitations associated with the permeability–selectivity trade-off in conventional polymeric membranes. Three CB[n]- based approaches are explored: inner structure modification, surface modification, and the addition of protective layers. These strategies leverage CB[n]’s selective binding properties and structural robustness to address key limitations in conventional polymeric membranes. The literature review examines current CO₂ separation technologies, emphasizing polymeric membranes and their performance challenges. Although CB[n] molecules are known for their CO₂ adsorption potential and structural stability, their application in membrane-based gas separation has been largely underexplored. This research addresses this gap by demonstrating how CB[n] incorporation can effectively overcome the permeability-selectivity trade-off while enhancing membrane durability. To tackle these challenges, CB[n] was embedded into polymer matrices and employed in surface modifications and protective layers. The first experimental chapter shows that CB[n]-based inner structure-modified polydimethylsiloxane (PDMS) membranes achieve improved CO₂ selectivity by providing additional interaction sites. The second chapter demonstrates that CB[n]-based surface modifications on PDMS membranes reduce surface energy barriers, thereby enhancing CO₂ permeation. The third chapter evaluates polyimide (PI) membranes with a CB[n]-based PDMS protective layer, resulting in superior separation performance and mechanical durability. The findings reveal that CB[n]-enhanced membranes not only improve CO₂ selectivity and permeability but also provide greater durability and cost-effectiveness, making them viable for large-scale applications. Moreover, the CB[n]-based modification process integrates seamlessly into existing membrane fabrication workflows without requiring additional capital investments. Ultimately, this research highlights the transformative potential of CB[n] in advancing polymeric gas separation membrane technology, contributing to cost-effective CO₂ capture solutions and supporting global net-zero emission targets.

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