Polyethyleneimine‐Mediated Polyamide Composite Membrane with High Perm‐Selectivity for Forward Osmosis

Abstract Thin‐film composite (TFC) membranes comprised of a polyamide (PA) selective layer upon a porous substrate dominate the forward osmosis (FO) membrane market. However, further improvement of perm‐selectivity still remains a great challenge. Herein, a polyethyleneimine (PEI) interlayer is intentionally designed prior to interfacial polymerization (IP) to tailor the PA layer, which thus improves the separation performance. The PEI interlayer not only improves the substrate hydrophilicity for adsorbing more diamine monomer and controlling its release rate, but also participates in IP reaction by crosslinking with acyl chloride (TMC). Furthermore, it can decrease the electronegativity of the substrate for decreasing reverse salt diffusion. Consequently, a denser, thinner and smoother PA layer is formed due to the uniform distribution, controllable release of diamine monomer and the extra crosslinking between PEI and TMC. Furthermore, the PA layer becomes more hydrophilic with PEI involvement. As a result, the asprepared TFC membrane exhibits a favorable water flux of 16.1 L m −2 h −1 and an extremely low reverse salt flux (1.25 g m −2 h −1 ). Meanwhile, it achieves an excellent perm‐selectivity with a ratio of water to salt permeability coefficient of 8.25 bar −1 . Moreover, it exhibits an outstanding antifouling capacity. The work sheds light on fabricating high perm‐selective membranes for desalination.