Highly permeable and acid-resistant nanofiltration membrane fabricated by in-situ interlaced stacking of COF and polysulfonamide films

The fabrication of nanofiltration (NF) membranes with excellent acid resistance and high separation performance remains a tremendous challenge due to the lack of precise membrane structure manipulation. Herein, covalent organic frameworks (COFs), due to their abundant porosity and highly ordered structures, are employed to synthesize high-permeation nanofiltration membranes. An acid-stable COF layer and a polysulfonamide (PSA) layer were fabricated by in-situ interfacial polymerization (IP) upon the polyethersulfone (PES) ultrafiltration substrate in turns. The acquired COF-based composite membrane exhibited sub-nanometer pore size and excellent rare-earth ions separation performance due to the interlaced stacking between the COF and PSA layers, as well as the COF interlayer regulated IP process. Additionally, the composite membrane showed high rejection of >92.2% for trivalent rare-earth ions (RE3+) and high water permeance of >43.3 L h−1 m−2 bar−1 at both pH = 6.8 and pH = 1, the superior separation performance can be ascribed to the high porosity and abundant transportation pathway provided by the COF layer and the interlaced stacking structure between the COF layer and the PSA layer. The facile membrane fabrication procedure, along with the excellent water permeation performance and acid resistance, render the composite membrane in this study applicable for a broad range of critical industrial and environmental processes.