(396v) Fabrication of Silica Nanoparticle-Stacked Ultrafiltration Membrane Using Spin-Assisted Layer-By-Layer Method

Ultrafiltration (UF) membranes are widely applied for industrial use to separate dispersed materials such as particles and colloids from water. Commercially available UF membranes are mainly prepared with organic polymeric materials by a phase-separation method. These conventional membranes have a thick separation layer over several hundred nanometers, therefore further improvement of water permeability has limitation. To overcome this limitation, a nanoparticle-stacked membrane was reported for ultrafiltration¹⁾. In this study, we demonstrate a novel fabrication technique of a silica nanoparticle-stacked inorganic UF membrane with an ultra-thin separation layer by using a spin-assisted layer-by-layer method.

  Silica nanoparticle-stacked UF membranes were prepared by a spin-assisted layer-by-layer method²⁾. A few drops of polydiallyldimethylammonium chloride (cationic polyelectrolyte) aqueous solution were deposited on an anodic aluminum oxide support membrane and then the excess solution was removed by the rotation at 3000 rpm using a spin coater. The membrane was rinsed with milli-Q water and dehydrated by ethanol to densify the membrane structure using the spin coater. Then, anionic silica nanoparticles prepared by hydrolysis and copolymerization reaction of tetraethyl orthosilicate were deposited on the membrane by the same operation as above. The nanoparticle-deposited membrane was calcined at 500^OC at 5 h. The membrane performance was characterized by water permeability and dextran rejection.

  The fabricated membrane had an extremely thin separation layer about several ten nm from FE-SEM observation. The thickness of the separation layer increased with the number of the stacked layer and decreased by the ethanol dehydration. The water permeability decreased with increasing the number of the stacked layer number while the separation performance was improved. The ethanol dehydration also remarkably improved the separation performance. These results indicate that the ethanol dehydration removed the hydration water of the polyelectrolytes and silica nanoparticles and densified the structure of the separation layer of the prepared membranes. The prepared membranes showed very high membrane performance than commercial organic or inorganic membranes.

Reference

1) X. S. Peng, et al., Nature nanotech., 4, 353-357 (2009)

2) C. Jiang, et al., Langmuir, 20, 882-890 (2004)