Tailored pore size and microporosity of covalent organic framework (COF) membranes for improved molecular separation

Three crystalline truxene-based ������-ketoenamine COF membranes (TFP-HETTA, TFP-HBTTA and TFP-HHTTA) are fabricated via a de novo monomer design approach to understand the fundamental correlations between pore structure and molecular separation performance. By introducing bulky alkyl groups into the truxene framework, the pore size of TFP-HETTA, TFP-HBTTA, and TFP-HHTTA are systematically tuned from 1.08 to 0.72 nm. Ac-cordingly, the TFP-HETTA showed good water permeance of 47 L m- 2 h- 1 bar- 1 along with a prominent rejection rate of Reactive Blue (RB, 800 Da) but less than 10% rejection rate of inorganic salts. In contrast, the TFP-HHTTA membrane with pore size of 0.72 nm can reject small dye molecules such as Safranin O (SO, 350 Da) and trivalent salts but with a moderate water permeance of 19 L m- 2 h - 1 bar- 1. The pore-flow model rooted from the viscous flow could well fit the observed organic solvent nanofiltration results of all three COF membranes.

Automated summary

By introducing bulky alkyl groups into the truxene framework, the pore sizes of three crystalline truxene-based ������-ketoenamine COF membranes were systematically tuned, leading to different water permeances and rejection rates for various molecules. The pore-flow model rooted from the viscous flow fitting the observed organic solvent nanofiltration results indicates the fundamental correlations between pore structure and molecular separation performance in COF membranes.