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.

TiO2-deposited PES membrane prepared by layer-by-layer coating.Figure optionsDownload as PowerPoint slideHighlights
► Layer-by-layer assembly of TiO2 nanoparticles on nanoporous films.
► Drastically improved stability of developed membranes.
► Proven performance in nanofiltration.