Self-Aggregation Control of Porphyrin for Enhanced Selective Covalent Organic Network Membranes

Covalent organic networks (CONs) are considered ideal for precise molecular separation compared with traditional polymer membranes because their pores have a sharp molecular weight cut-off and a robust structure. However, challenges remain with regard to tuning pores as a prerequisite for facile membrane fabrication to a defect-free layer. Herein, a highly conjugated amino-porphyrin is used and exploited its tunable stacking behavior to fabricate porphyrin-based polyamide CONs with ordered structures through interfacial polymerization with acyl chlorides. Controlling the self-aggregation behavior of the porphyrin and the conformation of the acyl chlorides can create different covalent networks. Acid-triggered porphyrin protonation offsets stacking to reduce the pore in the network from mesopore to micropore, enabling selective molecule transport. Furthermore, different acyl chloride ligands are used to control the interlayer bonding in CONs. Accordingly, the tailored pore diameters (0.48-0.78 nm) are confirmed by the molecule rejections with performance stability over 25 days of operation, as well as under various conditions. This study leverages porphyrin chemistry and interfacial polymerization to fabricate a defect-free CON layer with a significantly lower molecular weight cut-off (< 330 Da) than previously reported porphyrin-based membranes (>800 Da). This will pave the way for the development of ideal topological membranes.