Growing to Shrink: Grafting alumina mesopores for molecular separations

Abstract

Hybrid, ceramic-based membranes combine the stability of porous ceramic oxides with the functionality of polymers. The wide range of polymers allows for tailor-made materials matching the requirements of the target application. This thesis expands upon the materials, fabrication techniques and potential applications of hybrid, ceramic-based membranes. Chapter 2 first gives an overview of the recent progress in grafted ceramics for organic solvent nanofiltration (OSN) applications. It provides an overview of suitable organic-inorganic linking functions, reviews the strategies to tune the pore surface and compares the resulting membranes. Also discussed are the capabilities and shortcomings of both the characterization tools and the transport models used to describe this class of membranes. The link between material chemistry, grafting technique and performance is established as the challenges awaiting the researcher of hybrid, ceramic-based membranes are identified. This chapter serves to frame the advances presented in the following Chapters for the reader. Chapter 3 presents the grafting-from technique applied to the confined mesopores of ɣ-alumina. It is the first instance of controlled polymerization initiated from the surface of a high-curvature concave geometry. Polystyrene was grown inside 5 nm diameter pores to shrink to a desired degree, demonstrating the ability to tune the membrane selectivity. The parameters choices of the method used-surface-initiated, activators-regenerated-by-electron-transfer, atom-transfer radical polymerization (SI-ARGET-ATRP)-are detailed. The graft is characterized by TGA, AFM, and FTIR, and it is shown that the graft length is solvent-dependent. Also demonstrated is the application potential of this new class of hybrid, ceramic-based membrane as an organic solvent nanofiltration membrane. The top performing membrane exhibited a toluene permeability of 2.0 L.m-2 h-1 bar-1 accompanied by a 90% retention of diphenylanthracene (MW 330 g mol-1). Chapter 4 features further development of the grafting-from method with a novel material and for a different application, poly(ionic liquid) [StyMim][Tf2N] for CO2 separation. The same support substrate as Chapter 3 was used for SI-ARGET-ATRP, although adjustments to the reaction reagents and parameters were required. These are explained alongside the gas transport behavior through membranes made by successive polymerizations. The dense-pore gas separation membrane is characterized by means of AFM, XPS, SEM/EDS, and FTIR. A CO2 permeance of 0.47×10-7 (mol.m-2 s-1 Pa-1) and a CO2/N2 permselectivity of 14 was achieved, providing an encouraging beginning for development of this new membrane class. Chapter 5 presents two new unique achievements: a thioether-based aromatic crosslinked selective layer, and a green interfacial polymerization (IP) technique. Before this work, toxic solvents were use for the production of chemically and thermally resistant nanofiltration membranes. The use of non-toxic solvents for the synthesis of these membranes w...