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 C--O in TpPa-1 positively improved the water flux.

Automated summary

A new separation membrane was developed by superimposing two COF-based films with different aperture sizes. The double-layer superimposition membrane exhibited high water flux and salt rejection rate, overcoming the trade-off effect. The composite membrane had combined advantages of the two COF materials, with significantly higher water permeance and 100% salt rejection rate compared to conventional reverse-osmosis membranes.