High flux thin film nanocomposite membranes based on porous organic polymers for nanofiltration

Micro-porous organic polymers have garnered tremendous interest in membrane design because of their high nanoscale porosity, superior polymer affinity and chemical stability. In this study, o-hydroxy porous organic polymer (o-POP) utilized as nanofillers were introduced to thin film nanocomposite (TFN) membranes via an interfacial polymerization (IP) process. The o-POP with abundant phenolic –OH limited the diffusion rate of aqueous monomers toward the organic boundary via the robust interactions of electrostatic attraction and hydrogen bonding, as well as increased viscosity of aqueous phase, leading to formation of a regularly crumpled ring-shaped surface and causing a slightly increase in the average pore size of the membrane surface of 0.482 ± 0.03 nm. Such larger pore size surface with abundant bubble, tube or annular pipe structure thus distinctly elevates water transport through the membranes. More importantly, a TFN membrane containing 0.02 wt% o-POP was found to have a high water permeability (29.9 L m−2 h−1 bar−1) and an excellent bivalent salt rejection (97.5% for Na2SO4), which was three times higher than the water permeability of a commercial nanofiltration (NF) membrane.