Covalent organic frameworks (COFs) has shown great potential as stationary phase in gas chromatography separation. However, designing COF stationary phases with high separation performance remains challenging. Here, we report a novel strategy to enhance the separation ability of COF stationary phases through tuning the interlayer stacking of COF. A rare interlayer modulation of 2D COFs from eclipsed-AA to slipped-AA was achieved through a two-step synthesis method. Simply changing the solvent used in step 1 allowed an interlayer modulation from slipped-AA to eclipsed-AA. As the proof-of-concept, 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (Tph) and 2,5-dihydroxyterephthalaldehyde (DHTA) were condensed to prepare 2D COF Tph-DHTA. The interlayer stacking of the 2D COF Tph-DHTA was tuned from eclipsed-AA model to slipped-AA by changing the solvent from o-dichlorobenzene + n-butanol (3:1, v/v) to tetrahydrofuran + n-butanol (1:7, v/v) in step 1. The as-prepared Tph-DHTA with slipped-AA stacking (s-Tph-DHTA) showed higher resolution and faster separation of C8 aromatic isomers than that with eclipsed-AA stacking (e-Tph-DHTA). The formation of slipping stacking of s-Tph-DHTA facilitated the thermodynamics, but did not affect the mass transfer resistance for the separation of C8 aromatic isomers. This work not only provides a promising way to modulate the stacking structure of COFs, but also opens a new strategy to design COF stationary phases for the separation of intractable isomers.
Read full abstract