Membrane separation plays a crucial role in a wide range of industries, yet conventional materials such as polymers and ceramics face challenges in attaining high production rates and separation efficiency. These materials do not offer optimal transport capabilities as the resulting membranes lack well-structured and adjustable pore channels, resulting in a non-uniform pore size, limited porosity, and inadequate interconnectivity. The limitations of these materials have led to the exploration of alternative options, such as covalent organic frameworks (COFs). COFs have emerged as a new class of crystalline materials for membrane separation due to their well-defined pore structure, high porosity, highly tunable surface chemistry, and excellent chemical stability. However, the processing of COFs into a composite membrane has been limited by the challenges associated with the selection of appropriate substrate materials and the lack of effective methods for forming defect-free thin films with long-range order. This thesis aims to investigate the fabrication methods for COF-based thin film composite (TFC) membranes using ceramic hollow fibres (CHFs) as substrates, focusing on three processing methods: in-situ growth, interfacial polymerisation, and vacuum-assisted self-assembly.
Initial research focuses on optimising CHF substrates for COF deposition. The study then progresses to in-situ growth, examining imine-linked COF-LZU1 and COF-300 for intergrown COF layer formation and assessing separation efficiency via pervaporation of azeotropic mixtures. Interfacial polymerisation is subsequently analysed as a method to create COF thin films directly on CHF substrates, targeting applications in textile wastewater filtration. Lastly, vacuum-assisted self-assembly is investigated for developing thin, crystalline COF films, with an emphasis on ketoenamine-linked COF, TpPa-SO3H, for removing small pharmaceutical molecules through size exclusion and electrostatic repulsion.
The primary goal of this thesis is to advance the development of COF/CHF membranes for fluid separations and deepen the understanding of their fabrication processes and properties.