Highly flexible and robust self-standing covalent organic framework (COF) membranes with rapid preparation are important but technically challenging for achieving precise separation. Herein , a novel imine-based 2D soft covalent organic framework (SCOF) membrane with a large area of 226.9 cm 2 , via ingeniously selecting an aldehyde flexible linker and a trigonal building block, is reported. The soft 2D covalent organic framework membrane is rapidly formed (≈5 min) based on the sodium dodecyl sulfate (SDS) molecular channel constructed at the water/dichloromethane (DCM) interface, which is the record-fast SCOF membrane formation and 72 times faster than that in the reported literature. MD simulation and DFT calculation elucidate that the dynamic, self-assembled SDS molecular channel facilitates faster and more homogeneous transfer of amine monomers in the bulk, thereby forming a soft 2D self-standing COF membrane with more uniform pores. The formed SCOF membrane exhibits superb sieving capability for small molecules, robustness in strong alkaline (5 mol L −1 NaOH), acid (0.1 mol L −1 HCl), and various organic solutions, and sufficient flexibility with a large curvature of 2000 m −1 for membrane-based separation science and technology.
Covalent organic frameworks (COFs) are an emerging class
of crystalline
porous materials with low density, high porosity, and excellent physicochemical
stability. Recently, smart COFs with special structures and functional
groups have been widely concerned, which can respond to external stimuli
such as pH, temperature, light, gas, etc. However, it is still a paramount
challenge to fabricate smart COF membranes possessing the advantage
of alternating the pore size to realize gradient separation of multiple
organic pollutants. In this work, we fabricated a 2D amine-linked
smart COF membrane coupling hardness with softness via interfacial
polymerization under room temperature and atmospheric pressure conditions.
Interestingly, these COF membranes show higher dye rejection performance
in water than in acetone, and the pore size of smart COF membranes
can be dynamically regulated by different solvents. Powder X-ray diffraction
(PXRD) was used to identify the intrinsic structure change of this
intriguing phenomenon. By serendipity, we found that the PXRD peak
shifted to a lower degree when the membranes were immersed in acetone
than in water, suggesting enlargement of the pore size due to flexible
frameworks. The dynamic enlargement of the pore size was reversible
when the solvent was switched from acetone to water. This study not
only provides a frontier of smart COF membranes but also broadens
potential applications of COF materials.
Hydrogen is an important energy carrier for the transition to a carbon-neutral society, the CMS membrane exhibited ultrahigh H2/N2 selectivity (117) and H2 permeability, which have bright prospects for hydrogen purification.
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