Tuning the porosity and functionality of polymeric membranes for filtration and fouling analysis

Abstract

The growing demand for potable water continues to diminish available freshwater resources. Membrane filtration offers a promising solution by delivering high-purity water through the effective removal of emerging contaminants and organic matter. The performance of a membrane in specific filtration applications depends largely on its pore structure, functional attributes, and surface properties. This thesis focuses on the development of multifunctional membranes by tailoring their pore structures and evaluating their applicability in water treatment, with an emphasis on solute transport and fouling mechanisms. The first objective involved literature-based analysis of biomimetic membrane modification strategies and evaluating their effectiveness in water purification. Materials such as aquaporins, dopamine, and peptoids emerged as promising candidates for applications in desalination, oil–water separation, and heavy metal removal. However, challenges such as membrane fouling and the complexity of replicating biological cell structures remain unresolved. The second objective examined the experimental structure–performance relationship of hydrogel-filled membranes, where hydrophilic–hydrophobic monomer-based hydrogels confined within microfiltration pores induced hierarchical porosity and enhanced membrane flux. Stability tests and ion interaction studies demonstrated the suitability of these membranes as industrial pre-treatment options for reverse osmosis systems. Reflection coefficients and salt permeability were further evaluated using the Spiegler–Kedem–Katchalsky model based on experimental flux and rejection data. The membranes also showed potential in oil recovery applications when tested against oily water feeds. In the third phase, silver nanowires were incorporated into electrospun nanofibrous membranes to investigate fouling behavior in the presence of natural organic matter. The nanofibrous membranes showed potential to complement traditional ultrafiltration and microfiltration systems. Fouling models applied to these membranes identified ‘cake formation’ as the dominant fouling mechanism, with silver nanowire loading directly influencing the fouling coefficient. The fourth objective explored the role of the Zn-based metal–organic framework (MOF), CALF-20, in modifying ultrafiltration membrane pore structures to improve solute rejection. The CALF-20 reduced pore size and promoted uniform pore distribution. Pore hindrance models were subsequently applied to estimate convection and diffusion resistances as well as theoretical solute rejection. Collectively, these membrane systems exhibit strong potential for industrial applications involving size-selective solute removal.