Nanoparticles as Sacrificial Pore Fillers for the Fabrication of High-Permeability Polyelectrolyte Multilayer Membranes

Polyelectrolyte multilayer (PEM) membranes have shown great promise in a wide range of membrane-based separations. However, a continuous challenge is the permeability-selectivity trade-off. One method of avoiding this trade-off is by reducing the thickness of the selective layer. However, PEM membranes have a limit to this reduction, as they first have to fill the pores of their support membrane before they can form a defect-free selective layer. To overcome this limitation, we propose the use of nanoparticles as sacrificial pore fillers. Therefore, we first coated SiO₂ nanoparticles in the initial bilayer of a poly(diallyldimethylammonium chloride)/poly(sodium 4-styrenesulfonate) PDADMAC/PSS PEM to fill the pores of the support membrane and prevent subsequent PDADMAC/PSS bilayers from entering. Subsequently, we dissolved them in a NaOH solution. The results show that the optimal membrane, formulated with 12 nm sacrificial nanoparticles, successfully enhanced the permeability up to 2× (achieving 24 L m^–2 h^–1 bar^–1) while maintaining a comparable molecular weight cutoff (MWCO) of 312 Da. Membranes showed a slight change in ion retentions as the negatively charged membranes lost some of their overall charge due to the dissolution of the negatively charged SiO₂ nanoparticles. However, Donnan exclusion remained the dominant separation mechanism. These results establish nanoparticles as effective sacrificial pore fillers, enabling PEM membranes to achieve superior performance compared to commercial nanofiltration membranes by reducing their energy requirements in separation processes.