Solvent‐Induced Deformation of Aramid Nanofibers for Ultrahigh‐Flux Nanofiltration Membranes

Abstract Aramid nanofibers (ANFs), as promising organic nano building blocks for their high mechanical strength and thermal stability, are widely applied to fabricate energy‐efficient membranes for ionic and molecular sieving in aqueous solutions. However, the existing ANFs often have small diameters, limiting the permeability of the resulting membranes. Here, the ANFs with a diameter in the hundred‐nanometer scale are fabricated through a progressive protonation process, in which dimethylformamide as a secondary deprotonation solvent is added into dimethyl sulfoxide to provide a mild deformation environment. Then, the deformed ANFs are applied to prepare membranes with a larger pore size distribution and higher surface charge. Notably, the water flux of the resulting membranes can reach up to 410 L m −2 h −1 bar −1 , which is 40 times higher than commercially available nanofiltration membranes and much higher than currently reported ANF‐based membranes. Impressively, these membranes with super‐stable nanochannels maintain a high water flux of over 194 L m −2 h −1 bar −1 in a wide range of pH values from 4 to 10 and show excellent long‐term durability over 120 h. The application of deformed ANFs provides a new and promising approach for designing the next generation nanofiltration membranes which balance the trade‐off between permeability and selectivity.