Nanofiltration through cylindrical nanopores end-grafted with polyelectrolytes

Taking account of the effects of polyelectrolytes friction, osmotic pressure, and dielectric saturation, a continuum model is adopted to investigate the rejection and permeability of cylindrical nanopores end-grafted with pH-regulated polyelectrolytes (PEs). In addition to a detailed simulation for the behavior of the system considered under various conditions, the intriguing phenomena and underlying mechanisms are also discussed. The results gathered suggest that end-grafted nanopores show a better rejection than the corresponding bare nanopores, and the real rejection is dictated by the mean volumetric flux. Complete coverage of PEs over the cross section of a nanopore will not improve its rejection due to the hindrance in flow rate. However, both partial grafting of nanopore feed side and reducing membrane thickness can promote permeability and maintain the level of rejection. The rejection for the case where the subunits of a PE layer are localized near the outer ring of a nanopore cross section is better than that for the case where they are localized near its inner ring. The former also shows a higher permeability than the latter. By end-grafting a nanopore with 8-nm radius, its rejection for 100 mM KCl is comparable to that for a bare nanopore with 2-nm radius, although the flow rate in the former is one-order-of-magnitude larger than in the latter. This reveals that end-grafting has the potential for enlarging nanopore, thereby opening a new avenue of raising permeability while maintaining rejection simultaneously.