The underlying mechanism insights into support polydopamine decoration toward ultrathin polyamide membranes for high-performance reverse osmosis

The development of ultrathin polyamide (PA) nanofilms with desirable water permeance and high selectivity has been recognized as crucial for energy-efficient desalination of salty water and wastewater reclamation. In this study, an ultrathin PA reverse osmosis membrane (∼25 nm) was fabricated via polydopamine (PDA) interlayer-mediated interfacial polymerization onto a polyethersulfone (PES) substrate. The ultrathin PDA interlayer was soldered in situ onto PES substrates by precisely controlling the ammonia-initiated self-assembly process. Furthermore, the PDA interlayer conferred a high-density uptake toward aqueous amine monomers and served as a quasi-molecular-scale regulator that mediated their diffusion into the organic phase to polymerize with the acyl chloride of 1, 3, 5-benzenetricarbonyl trichloride (TMC). The synergistic effects triggered self-sealing and inhibited membrane growth, promoting the formation of an ultrathin and defect-free PA nanofilm with a hierarchical nanostripe surface. The newly developed membranes exhibited a desirable water permeance of up to 1.44 L m−2 h−1·bar−1, almost triple that of the pristine PA membrane (0.44 L m−2 h−1·bar−1), and a simultaneously enhanced rejection ratio of 99.2% toward NaCl. This work sheds light on strategies to develop ultrathin PA-based membranes with high water permselectivity for environmental- and energy-relevant applications.