Facile surface modification of nanofiltration membranes to target the removal of endocrine-disrupting compounds

Poor rejection of organic micropollutants and, in particular, endocrine-disrupting compounds (EDCs) by many NF membranes may pose limitations on their use in many potential applications. This report considers modification using concentration polarization-enhanced surface graft-polymerization as a possible means to improve the removal of organics by commercial NF membranes. This approach was examined using NF270 membrane, two monomers commonly used for grafting, 3-sulfopropyl methacrylate (SPM) and 2-hydroxyethyl methacrylate (HEMA), and two common EDCs; bisphenol-A and metolachlor. In all but one case a substantial reduction of solute passage along with some drop in flux was observed demonstrating feasibility of the grafting approach. The amount of grafted polymer on the surface well correlated with monomer concentration used, however, the largest improvement of EDC rejection was obtained already at the lowest concentration with little or no improvement for larger grafting. A similar, but not as large, variation with grafting was observed for water flux. These results are explained using a model that assumes existence of a small fraction of more permeable and less selective areas in the membrane (“defects”) that are rapidly plugged upon grafting. Such plugging should be particularly effective using the concentration polarization-enhanced grafting. This facile method may be useful for modifying NF membranes for various purposes, particularly, for tailoring selectivity of commercial membranes and elements towards specific solutes.