Development of Thin-Film Nanocomposite Membranes with Metal-Organic Frameworks for PFAS Removal from Drinking Water

Sammanfattning

This thesis investigates the development of metal–organic framework (MOF)-modified thin-film nanocomposite membranes for potential PFAS removal from drinking water. The work focuses on how MOF type and loading influence membrane morphology, surface properties, and hydraulic performance when incorporated into a polyamide selective layer. Five MOFs, namely ZIF-8, ZIF-L, ZIF-94, NH₂-ZIF-8, and UiO-66-NH₂, were synthesized and evaluated as nanofillers in polyamide thin-film nanocomposite membranes prepared by interfacial polymerization on commercial polysulfone supports. The synthesized MOFs and prepared membranes were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and water contact angle measurements. Preliminary pure water flux screening was used to identify hydraulically workable membrane formulations before further crossflow filtration testing. The characterization results confirmed the successful synthesis of the selected MOFs and showed that MOF incorporation affected membrane morphology and wettability. ZIF-8-modified membranes displayed a relatively homogeneous morphology, whereas UiO-66-NH₂-modified membranes showed visible aggregation and defects. EDX analysis supported MOF incorporation through the detection of Zn in ZIF-based membranes and Zr in UiO-66-NH₂-modified membranes. Water contact angle measurements showed opposite wettability trends for the two main MOFs: ZIF-8 tended to increase the contact angle at higher loading, while UiO-66-NH₂ increased membrane hydrophilicity. Filtration results showed that membrane performance depended strongly on MOF identity, loading, and selective-layer integrity. ZIF-L and NH₂-ZIF-8 resulted in no measurable flux during preliminary screening, while ZIF-94 showed very low flux. ZIF-8 and UiO-66-NH₂ were therefore selected for further evaluation. UiO-66-NH₂ at 0.1% (w/v) showed the highest initial water permeability among the PA-coated membranes, but this result should be interpreted with caution due to visible defects and aggregation. In contrast, ZIF-8 at 0.1% (w/v) showed the most balanced hydraulic performance, combining relatively high water permeability, low fouling factor, good hydraulic recovery, high PFAS filtration flux, and more homogeneous morphology. Overall, this work demonstrates that MOF incorporation can improve the hydraulic performance of polyamide nanofiltration membranes when the MOF type and loading are properly selected. ZIF-8 at 0.1% (w/v) was identified as the most promising formulation in this study.