Desalination behavior of composite membrane with petal shaped pore—formed by superimposition of covalent organic framework with large aperture difference

Covalent organic frameworks (COFs) are promising materials for developing the new generation of reverse-osmosis membranes owing to their unique structure with well-defined nanoporosity and highly tunable pore-wall chemistry. In this work, a new separation membrane was developed using the molecular dynamics (MD) simulation method by superimposing two COF-based films: HPB-COF (0.577 nm) and TpPa-1 (1.582 nm), with a large difference in aperture. The results showed that the new double-layer superimposition membrane could overcome the trade-off effect, and achieve a high water flux and salt rejection rate. According to the membrane model microanalysis, the HPB-COF divided TpPa-1 into six "petals", thus endowing the first layer and second layer of the membrane with a larger accessible surface area and smaller effective pore diameter, respectively. As a result, the new composite membrane simultaneously had combined advantages of the two COF materials. The water permeance of the TpPa-1/HPB-COF composite membrane was 1.85 times higher than that of the AB-stacked HPB-COF membrane, which was two orders of magnitude higher than that of other conventional reverse-osmosis membranes. The salt rejection rate was 100%, which was higher than that of AB-stacked TpPa-1 membrane (39.42%). Furthermore, the microanalysis revealed that the hydrophilic CO in TpPa-1 positively improved the water flux.