Effects of linking group on the desalination performance of three-dimensional covalent organic framework membranes

The structure and the hydrophilicity can be tuned by adjusting the linking group of a covalent organic framework (COF), which significantly affects the desalination performance of COF membranes. In this work, molecular dynamics (MD) simulation was used to investigate the effect of different NPN-X membranes with the same elements and different linking groups on desalination performance. The results showed that NPN-1 and NPN-2 membrane had superior desalination performance. The water permeances of NPN-1 and NPN-2 membrane were two orders of magnitude higher than those of conventional reverse osmosis membranes with a salt rejection rate of 100 %. The water permeances of the membranes were in the following order: NPN-2 > NPN-1 > NPN-3, although the NPN-3 had the largest pore size. The nature of the linking group played a crucial role in water permeance, and the high hydrophilicity of the pore wall of the membranes improved the water permeance. Moreover, the interaction between NPN-1 and NPN-2 membranes and ions was stronger than that of the NPN-3 membrane. Additionally, the pore shapes of NPN-1 and NPN-2 were more slender than NPN-3. This study provides valuable information for the subsequent desalination membrane structure design.