Ultrathin zwitterionic COF membranes from colloidal 2D-COF towards precise molecular sieving.

Membrane technology is an important component of resource recovery. Covalent organic frameworks (COFs) with inherent long-range ordered structure and permanent porosity are ideal materials for fabricating advanced membrane. Zwitterionic COFs have unique features beyond single ionic COFs containing anions or cations. Here, a zwitterionic colloidal 2D-COF (TpPa-Py) is synthesized via a single-phase method. ultrathin zwitterionic COF membranes are fabricated via a facile blade-coating method. Experimental and molecular dynamics simulation results showed that due to the unique amphiphilic nature of the TpPa-Py, the TpPa-Py membrane exhibits high level permeance and rejection of both positively and negatively charged dyes. Moreover, the TpPa-Py membrane exhibits excellent dye/dye and dye/salt separation performance. The selectivity factors were 89 for the separation of acid blue and rhodamine B, and 47.8 for the separation of methyl blue and NaCl. This work provides a promising solution for the development of high-performance membranes tailored for resource recovery of dye wastewater, addressing a critical need in water treatment.