Modulating the Interlayer Stacking of Covalent Organic Frameworks for Efficient Acetylene Separation.

Controllable modulation of the stacking modes of 2D (two-dimensional) materials can significantly influence their properties and functionalities but remains a formidable synthetic challenge. Here, an effective strategy is proposed to control the layer stacking of imide-linked 2D covalent organic frameworks (COFs) by altering the synthetic methods. Specifically, a modulator-assisted method can afford a COF with rare ABC stacking without the need for any additives, while solvothermal synthesis leads to AA stacking. The variation of interlayer stacking significantly influences their chemical and physical properties, including morphology, porosity, and gas adsorption performance. The resultant COF with ABC stacking shows much higher C 2 H 2 capacity and selectivity over CO 2 and C 2 H 4 than the COF with AA stacking, which is not demonstrated in the COF field yet. Furthermore, the outstanding practical separation ability of ABC stacking COF is confirmed by breakthrough experiments of C 2 H 2 /CO 2 (50/50, v/v) and C 2 H 2 /C 2 H 4 (1/99, v/v), which can selectively remove C 2 H 2 with good recyclability. This work provides a new direction to produce COFs with controllable interlayer stacking modes.