Enhanced Photocatalytic Activity of Porphyrin Nanodisks Prepared by Exfoliation of Metalloporphyrin-Based Covalent Organic Frameworks

Organic polymers derived from covalent organic frameworks (COFs) have various applications, including photocatalysis. The synthesis of organic polymer materials from COFs to obtain higher activity for photocatalysis by changing the unit molecule has been investigated. The choice of the unit molecule is important to characterize the photochemical properties. Among various such unit molecules, porphyrins have attracted much attention as organic chromophores commonly used in photocatalytic reactions with COFs. Although COFs with various organic chromophores have been synthesized and attempts have been made to improve their photocatalytic activity, enhancing the photocatalytic activity by adjusting the layer thickness through exfoliation of COFs has yet to be fully studied. In the present study, the exfoliation of metalloporphyrin-based COFs with pyridine as the axial ligand and adjustment of the layer thickness were found to enhance the photocatalytic activity. Hydrogen generation and 3,3',5,5'-tetramethylbenzidine oxidation reactions were investigated as representative photocatalytic reactions, with the photocatalytic activity up to 7 times that of the original free-base porphyrin COFs. These results indicate that the different thicknesses synthesized by exfoliating COFs increased the photocatalytic effect of polymers.