Embedding TiO2 nanoparticles versus surface coating by layer-by-layer deposition on nanoporous polymeric films

Hybrid polymeric films based on titania (TiO2) nanoparticles on a polyethersulfone (PES) support were obtained by embedding nanoparticles, by dipping in a single layer and by layer-by-layer assembly. First, TiO2 nanoparticles were doped into a polymeric film during phase-inversion. The permeate flux of TiO2-embedded membranes in (nano)filtration was higher than for the bare PES membrane in the ultralow concentration range of TiO2 nanoparticles (0.035-0.125 wt.%). At the highest concentration of TiO2 nanoparticles tested (0.375 wt.%), however, the permeate flux decreased significantly. Compared to the TiO2-embedded membrane, the permeate flux of TiO2-deposited membranes prepared by dipping in one single layer was relatively low. After applying layer-by-layer coating, the permeate flux increased considerably as the number of coating layers was increased to >10. SEM images showed that addition of TiO2 nanoparticles during phase inversion resulted in larger finger-like pores in the membrane structure, without changing the surface structure. TiO2-deposited PES membranes prepared by the layer-by-layer coating proved to have a porous coating layer of TiO2 nanoparticles, covering the surface completely. The surface of TiO2-deposited films proved to be less rough than that of the bare PES membranes. Release of TiO2 nanoparticles from the membrane surface was not observed during cross-flow filtration, indicative of strong binding of TiO2 nanoparticles on the membrane surface. Similar rejections of humic acid were observed for bare PES membranes and TiO2-multilayer coated PES membranes, confirming that the membrane structure was not damaged by increasing the number of coating layers of TiO2 nanoparticles on the membrane surface. (c) 2013 Elsevier Inc. All rights reserved.