Interfacially polymerized nanofiltration membranes: Atomic force microscopy and salt rejection studies

Interfacial polymerization is one of the main techniques for producing composite nanofiltration (NF) membranes. In this study, five NF membranes were produced through interfacial polymerization under different conditions of reactions, namely varying reaction time, as well as monomer concentrations. The membranes were then imaged using atomic force microscope (AFM). AFM images provided information of the average pore size, pore size distribution, and surface roughness. For some of the membranes, discrete pore sizes were visible. Increasing the reaction time resulted in decreasing water permeabilities but based on AFM imaging the pore size was of similar value. Increasing the monomer concentration also resulted in de creasing water permeabilities. However, based on AFM imaging the pore size differs considerably. Additional permeation experiments were also carried out using NaCl and Na₂SO₄ solutions with membranes identified as NF. By fitting the rejection data using a model such as the Donnansteric-pore model, the variation in effective charge density of the membranes was also determined. The ability to tailor composite NF membranes with the right properties will significantly improve membrane performance.