Abstract
This research work focused on the roles of functionalised zeolite on the substrate and selective layer of thin-film composite membranes development for salt removal from water. Due to the reduced water sources, in the current water purification technology, it is important to explore available and alternative water sources for consumption and other related domestic use. As such, the current membrane development is a promising water purification technology. In this research work, the colloidal silica, fumed silica and tetraorthosilicate (TEOS), were used as silica sources for hydrothermal synthesis of different ZSM-22 Theta-1(TON) zeolite materials with different silica to aluminium (Si/Al) ratios of 30, 60 and 90 as potential additives due to their effective use in water treatment as adsorbents or ion exchanger. The study looked into the effects of both the silica precursor and the Si/Al ratio on the structural development, formation and surface properties of the obtained different (Zeolite Scouny Mobil 22) ZSM-22 TON-type zeolite materials. The XRD, BET, TGA, FTIR, SEM/EDX, and TEM were used to characterise the resulting ZSM-22 zeolite materials and validated the development of well-defined and ordered structures. From each silica source, ZSM-22 of Si/Al ratio of 60 was then selected as a potential zeolite filler material in the development of zeolite-polyethersulfone (ZSM-22/PES) ultrafiltration (UF) membranes, ZSM-22/PA@ZSM-22/PES, and H2N-ZSM-22/PA@Z-PES composite thin-films. The ZSM-22 filler material is a microporous, aluminosilicate mineral that is often employed as adsorbents and catalysts and in this study proved to be particularly effective in the production of both UF membranes and composite thin-films. For ZSM-22/PES preparation, the phase inversion preparation method was then used in, which C60-ZSM-22, F60-ZSM-22, and T60-ZSM-22 as filler materials were, respectively incorporated into the polymer matrix, resulting in anisotropic UF membranes. The zeolite ZSM-22 filler served as a cross-linker for the polyethersulfone (PES) polymer, resulting in improved PES UF membrane performance. The obtained ZSM-22 with Si/Al of 60 as filler was also functionalised with amino-silane as a potential cross-linker with the polyamide (PA) chains in the development of composite thin-film nanofiltration (NF) membranes for effective salts rejection as a continuous attempt at membrane development. Membranes with increased water flux in the range of 200 to above 700 L.m2.h-1 and 80% flux recovery ratios or increased protein (BSA)
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fouling resistance exhibited increased hydrophilicity with increasing amounts of ZSM-22. In the assessment of ZSM-22/PES UF membranes, the dead-end solute rejection for monovalent NaCl was unaffected by filler loadings, whereas for the divalent salt, MgCl2, it reached a peak before declining as loading increased. The utilised UF membrane materials viz., T60-ZSM-22/PES (Chapter 5) and C60-ZSM-22/PES (Chapter 6), as well as F60-ZSM-22/PES (Chapter 6), achieved a minimum rejection of roughly 55%. The observed performance of the generated composite thin-films NF membranes exposed to cross-flow fusing, further supported the improvement in UF membrane performance when utilised as UF supports. The observed performance of the produced composite thin-films NF membranes upon subjected to cross-flow filtration attained flux permeability into about 100 000 L.m2.h-1., The membranes also exhibited a negatively charged surface, reduced permeable (due to the compromised/compacted macrovoids), and enhanced salt separation ability, further supporting the improvement in UF membrane performance. Permeability enhancements of the obtained composite thin-film NF membranes followed the order: H2N-ZSM-22/PA@C60-ZSM-22/PES > H2N-ZSM-22/PA@F60-ZSM-22/PES > H2N-ZSM-22/PA@T60-ZSM-22/PES, while rejection ability followed the order: H2N-ZSM-22/PA@C60-ZSM-22/PES > H2N-ZSM-22/PA@F60-ZSM-22/PES > H2N-ZSM-22/PA@T60-ZSM-22/PES for MgSO4 > AlCl3 > MgCl2 > NaCl, respectively. These thin-film composite membranes had a greater water flow and a salt rejection rate of over 80%. The T60-ZSM-22 nanoadditives provided better surface properties in this case; hence, the nature of the silica source, TEOS, and the nanoparticle size could provide a significant additional "degree of freedom" in building thin-film nanocomposites. The findings support the hypothesis that the ZSM-22 zeolite material (i.e. as-synthesised vs functionalised ZSM-22) silica precursor can alter the structural formation of the zeolite, potentially affecting the nanocomposite thin-films produced when they are directly incorporated during the interfacial polymerisation reaction.