Metal- Organic Frameworks as a Platform for Elucidating the Effects of Functional Sites on CO2 Interaction

Abstract

This thesis reports an investigation into metal-organic frameworks (MOFs) as candidate solid-state carbon dioxide capture materials. The modulation of CO2 uptake and heat of adsorption (|Qst|) were explored in response to the systematic variation of pore size, surface area and/or functionalisation in a range of targeted MOFs. Chapter 3 exploits ligand design and targeted MOF synthesis. Functionalised ligands based on the 4,4′-biphenyldicarboxylate core were generated through facile synthetic routes and incorporated into known MOF topologies, including the cubic UiO topology, the pillared paddlewheel topology and IRMOF-9 topology. Through the variation of metal, pore size and/or functionality in each of these series, general correlations between structure and degree of CO2 interaction with the adsorbate were elucidated. The problematic nature of unpredictable MOF self-assembly are also discussed Chapter 3, in which the synthesis, characterisation, and properties of four novel MOFs have been examined. Chapter 4 investigates post-synthetic modification (PSM) as an approach to generate more polar functional sites. PSM was undertaken in two framework types, microporous UiO-66 and mesoporous MIL-101, to investigate the effect of pore size on both the extent of PSM and its influence on CO2 uptake. In the mesoporous case, the polar functional sites increased CO2 uptake in all cases despite lower surface areas, suggesting that for larger pore frameworks, this is an effective strategy for enhancing CO2 uptake. Chapter 5 explores the potential for interplay between CO2 uptake and optical properties in MOFs through the use of CO2-reactive sites tethered to fluorophores in the porous structures. The results suggest that MOFs containing the arginine moiety are promising candidate CO2 chemosensors, as they exhibited strong linear fluorescence responses with increased CO2 dosing. This chapter presents a promising approach to the design of novel chemosensors.