Improved Water Flux and Separation of Polyamide Reverse Osmosis Membranes by Trace Loading of Biomimetic Modified Carbon Nanotubes

Pursuit of well-dispersed carbon nanotubes (CNTs) is of great significance since agglomeration of CNTs in aqueous solution and poor compatibility between CNTs and the polyamide (PA) layer are considered as the prominent drawbacks for the preparation of defect-free thin-film nanocomposite (TFN) membranes. In the present study, well-dispersed CNT porins (CNTPs) were successfully synthesized and then incorporated in the PA layer of TFN membranes. Raman and static test results showed that CNTPs exhibited better dispersion in aqueous solution than pristine CNTs, which could maintain stability for at least 15 days. Addition of CNTPs provided extra water nanochannels and slowed down the diffusion rate of m-phenylenediamine (MPD) to the organic phase, thereby contributing to the excellent increment in water permeability to 4.12 L/m2·h·bar, 1.93 times higher than that of TFC membranes. All of the TFN membranes exhibited unchanged salt rejection (above 99.1% for NaCl), implying little effect of soluble CNTPs on the membrane selectivity. Besides, TFN membranes exhibited not only satisfactory separation performance for NaF and H3BO3 and better chlorine resistance capacity but also great potential in the practical use of the desalination process. In all, this work presents an avenue for preparing defect-free CNT-based TFN membranes.