Year: 2009
Type: article
Abstract: Membrane technology has been used in water purification for decades. However, \nmembrane fouling remains a limiting factor. One way to control fouling is through \nsurface modification. Several studies report that increasing surface hydrophilicity can \nreduce membrane fouling. Surface modification via physical coating (i.e., thin-film \ncomposite membrane) was explored in this research to prevent membrane fouling. \nBefore making thin-film composite membranes, it was important to study \nstructure/property relations in a series of potential coating materials. This research aims \nto contribute to a better fundamental understanding of the structure/property relations \nwhich govern water transport, rejection of model foulants (i.e., emulsified oil droplet or \nprotein), and fouling characteristics in hydrogels based on poly(ethylene glycol) \ndiacrylate (PEGDA) and N-vinyl-2-pyrrolidone (NVP). \nCrosslinked poly(ethylene glycol) (PEG) free-standing films were prepared by \nUV-induced photopolymerization of PEGDA crosslinker in the presence of varying \namounts of water or monofunctional poly(ethylene glycol) acrylate (PEGA). The crosslinked PEGDA films exhibited polymerization induced phase separation (PIPS) \nwhen the water content of the prepolymerization mixture was greater than 60 wt%. \nVisible light absorbance measurements, water uptake, water permeability, and salt kinetic \ndesorption experiments were used to characterize the structure of these phase-separated, \ncrosslinked hydrogels. The films with PIPS exhibited a porous morphology in cryogenic \nscanning electron microscope (CryoSEM) studies. Dead-end filtration experiments using \ndeionized water and bovine serum albumin (BSA) solutions were performed to explore \nthe fundamental transport and fouling properties of these materials. The total flux of pure \nwater through the films after prior exposure to BSA solution was nearly equal to that of \nthe as-prepared material, indicating that these PEGDA films resist fouling by BSA under \nthe conditions studied. \nCrosslinked NVP free-standing films were prepared by UV-induced \nphotopolymerization in the presence of water, with NVP as the monomer and \nN,N’-methylenebisacrylamide (MBAA) as the crosslinker. A series of crosslinked films \nwere polymerized at various prepolymerization water contents, NVP/MBAA ratios and at \nvarious levels of UV light intensity in the polymerization. Like PEGDA, the NVP films \nalso underwent phase-separation during polymerization. The influence of monomer/ \ncrosslinker ratio, prepolymerization water content, and UV intensities on membrane \nmorphology and water transport was characterized with CryoSEM, bio-atomic force \nmicroscope (Bio-AFM) and dead-end filtration. Molecular weight cutoff (MWCO) \nmeasurements were used to characterize the sieving property of crosslinked NVP films \npolymerized at different UV intensities. UV intensity was found to have an impact on the \ninterconnectivity of crosslinked membranes. Finally, tests of fouling resistance to protein solution (bovine serum albumin) and oily water emulsion were performed. The NVP \ncrosslinked films had good protein and oily water fouling resistance. \nOverall, both crosslinked PEGDA and NVP films exhibit fouling resistance to \noily water emulsions or protein solution. NVP films had more porous structure and \nhigher water permeability than did PEGDA films, while the more compact structure of \nPEGDA films led to better rejection of model foulants (e.g., protein) than in NVP films. \nBased on different applications (e.g., oil/water separation, protein filtration), different \ncoating materials must be chosen according to the membrane morphology, transport \nproperty, and rejection of model foulants to achieve the highest water flux and foulant rejection in membranes used for water purification.
Author: Yuan-Hsuan Wu
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1630166702