How Imogolite-PVA Nanocomposite Membranes Can Impact Water Flux In Pressure And Thermally-driven Applications
By Ming Li, PhD candidate and Jonathan A. Brant, PhD
Membrane processes are widely used in water treatment for applications ranging from particulate separation to desalination. Persistent challenges for these processes include relatively high specific energy consumption, trade-offs between ion selectivity and water flux, and improving the chemical and physical robustness of membrane materials. Efforts aimed at overcoming many of these challenges, as well as others, have focused on the integration of engineered nanomaterials, such as zeolites, silica, silver, and carbon nanotubes into polymeric and ceramic matrices to create nanocomposite membranes (1).
In one example, researchers created a high-flux (~ 330 liters per square meter per hour (LMH) at 100 pounds per square inch gauge [psig]), high organic rejection (~99.8%) nanocomposite membrane using surface-oxidized carbon nanotubes (2-6). In this study, the active layer was a nanocomposite structure that incorporated carbon nanotubes into either a hydrophilic polyether-b-polyamide copolymer or a cross-linked polyvinyl alcohol hydrogel. The observed improvements in membrane performance were attributed to the presence of hydrophilic nano-channels in the active layer that served as preferential flow paths for water. These and other promising results have inspired the interest of many researchers in nanocomposite membranes for creating low-fouling, low-energy separation processes.
Nanotubes are an attractive type of nanofiller for making nanocomposite membranes because of their ability to enhance water transport across thin films (7). Previous studies have concluded that water transport is enhanced within the interior of carbon nanotubes (pore throat) because of the lack of friction between the water molecules and the hydrophobic interior of the nanotube (8). Unfortunately, the large-scale application of carbon nanotubes in membrane synthesis is limited by their tendency to aggregate in relevant solvents and manufacturing cost. These challenges have served as motivation for exploring the feasibility of using other types of nanotubes to create nanocomposite thin-films.
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