Surface modification of nanofiltration membranes by ion implantation

A composite polyamide NF membrane (NF 90 Filmtec) and a cellulose acetate NF membrane (SP 28 Osmonics) were implanted with F− ions at two different intensities-1E10 and 5E10 atoms/cm2. Zeta potential measurements of the unmodified membranes and modified membranes show higher negativity with an increased intensity of ion implantation. Multicomponent salt permeation experiments were performed with the three types of membranes-the unmodified membrane and the two types of modified ones for both NF 90 and SP 28. The results show a decrease of solute flux for all the ions through the modified membranes when compared to that with the unmodified membrane. Initial experiments show no leaching of F− ions into the solution. Therefore, ion implantation on nanofiltration membrane surfaces is a novel technique to increase the salt rejection property of membranes.