Dual-Functional Coating of Forward Osmosis Membranes for Hydrophilization and Anti-Microbial Resistance

Microbial fouling and internal concentration polarization (ICP) are factors limiting the performance of forward osmosis (FO) membranes. These limitations in flat sheet thin film composite (TFC) FO membranes were mitigated by a single Ag/AgCl nanocomposite coating in this study.  The coating was prepared by first adsorbing Ag⁺ on the negatively charged carboxylate groups of polyacrylic acid (PAA)-polyethersulfone (PES) blend membrane substrate (support layer). Cl^- ions were introduced next to form a conformal AgCl coating in-situ. Irradiation of the coating with visible light then converted it into a composite coating with Ag on the membrane substrate exterior and AgCl in the membrane substrate interior. The Ag/AgCl-coated membranes prepared as such delivered good antimicrobial resistance concurrently with a high water flux. The antimicrobial performance could be attributed to a high loading of nano-Ag on the membrane exterior while the high water flux to the AgCl hydrophilization of the membrane interior which reduces the ICP. To the best of our knowledge, this is probably the first demonstration of a dual-functional coating for FO TFC membranes.