MOF-based membranes for challenging gas separations

Abstract

Metal-organic framework materials (MOFs) have been extensively studied as adsorbents for carbon capture applications over past decades. However, when it comes to MOF-based membranes for CO₂ separation, factors that determine membrane performance are not limited to CO₂ adsorption capacity. Especially for mixed matrix membranes, other factors, such as MOF morphology, pore structure, and its compatibility with polymer materials are also of importance and should be considered in membrane design. The relevant background and literature review about the-state-of-the-art technology are provided in Chapter 1. In according to current research, various MOF materials with distinct properties have been applied for membrane-based gas separation in this PhD study, and their performance is discussed in Chapters 4 to 7.

In Chapter 4, two types of pure MOF membranes, crystalline and glassy, are introduced, however, they were difficult to work with and their membrane separation performance was not promising. Chapters 5 to 7 discuss the performance of MOFs as fillers in mixed matrix polymer membranes. MOFs were incorporated into two types of polymer at different loadings, namely PEBAX MH1657 and Matrimid®5218. The MOF materials can be classified into three types in terms of their morphology including nanoparticles (Chapter 5), nanoplates (Chapter 6) and nanosheets (Chapter 7). The incorporation of different MOF fillers generally achieved improvements in both gas permeability and some showed improvements in selectivity. A general conclusion is drawn in Chapter 8. In addition, the methodologies of MOF material and membrane preparation as well as material characterisation techniques are introduced in Chapter 3.