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Title: Improved nanofiltration membranes by self-assembly
Author: Cheng, S.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2005
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Charged ultrafiltration (UF)/nanofiltration (NF) membrane plays a very important role in membrane separation. Thus, the aim of the present study was to improve charged UF and NF membranes for increased application within the process, pharmaceutical and food industries. The main objectives of this work were to investigate the preparation, modification, characterisation and application of a group of charged UF/NF membranes. Substrate membranes were prepared with polyehterimide (PEI) and sulfonated poly(ether ether ketone) (SPEEK). The self-assembly deposition of polyelectrolytes on the membrane surface was also studied. No previous studies have so comprehensively assessed the fabrication and performance of self-assembly modified PEI/SPEEK membranes. The effects of small molecular additives were studied on membrane morphology and performance. Characterisation by scanning electron macroscopy (SEM) and atomic force macroscopy (AFM) showed that the addition of tetrahydrofuran (THF) and 1,4-dioxane induced a denser skinned top layer, which dramatically decreased the permeability. SPEEK was used to improve the hydrophilic properties of PEI membrane and permeability, as well as to provide surface charges. The membrane properties were very reproducible when the proportions of SPEEK were 3% and 6% in the total polymer content. Positively and negatively charged NF membranes were fabricated by self-assembly. Positive NF membrane was obtained by depositing polycation, polyethylenimine, on the surface of PEI/SPEEK blend membranes. The effects of Ph and ionic strength of the polyelectrolyte solution on the membrane performance were investigated and it was concluded that the high amount of adsorption of weak polyelectrolyte on the membrane surface with opposite charges was achieved close to the isoelectric point (IEP). Again, negatively charged NF membrane was fabricated by depositing poly (acrylic acid) (PAA) on the surface of positively charged membranes. Zeta potential measurements showed that the deposition of polyelectrolytes changed chemistry of the membrane surfaces. The pore sizes calculated from rejection data using and from AFM demonstrated that the adsorption of polyelectrolytes on membrane surfaces led to the decrease of pore size. The present study has shown the advantage of using phase imaging to characterise membrane morphology; the identification and sizing of pores was easier than when using standard topography. No other studies have used this technique to study pore sizes. Methylene blue (MB) and sodium cefuroxime were used to explore the industry application of obtained membranes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available