A robust COF membrane on polyethylene support via ethanol-assisted self-assembly of COF nanosheets for efficient desalination

Fabrication of high-rejection covalent organic framework (COF) membranes for desalination remains a significant challenge, due to processing limitations and substrate mismatches. Herein, we report an ethanol-assisted self-assembly strategy for preparing high-rejection COF membranes from anionic TpPa-SO3Na COF (SCOF) nanosheets. This method promotes SCOF dispersion in ethanol with high aspect-ratio structures and elimination of interlayer charge, thus facilitating the formation of defect-free SCOF membranes (COFMs). Furthermore, polyvinyl alcohol (PVA) was used to modify commercial polyethylene (PE) supports ensuring compatibility with the high-rejection SCOF layers. The hydrophilic PVA@PE support with appropriate surface pore induces the SCOF nanosheets to form a complete stacking structure. The resultant COFM (MEtOH) exhibit an impressive Na2SO4 rejection rate of 98.83 % and a pure water flux of 4.35 L m−2 h−1, demonstrate exceptional rejection stability under elevated pressure, acidic or alkaline conditions, and high salt concentrations. The superior desalination performance of the COFMs surpasses the most reported 2D desalination membranes.